Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools


[Document Version: 2.07] [Last Updated: 05/25/1998]

Chapter 1) About the Author & Copyright

Notes on the Troubleshooting and Repair of Small Household Appliances and Power Tools

Author: Samuel M. Goldwasser
Corrections/suggestions: | sam@stdavids.picker.com

Copyright (c) 1994, 1995, 1996, 1997, 1998
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.

Chapter 2) Introduction

  2.1) Where do you keep your dead appliances?

If you have ever tried to get a small household appliance or portable power
tool repaired, you understand why all that stuff is likely to be gathering
dust in your attic or basement closet or junk box.  It does not pay!  This
may be partially by design.  However, to be fair, it may take just as much
time to diagnose and repair a problem with a $20 toaster as a $300 VCR and
time is money for a repair shop.  It is often not even economical to repair
the more expensive equipment let alone a $40 electric heater.  The cost
of the estimate alone would probably buy at least one new unit and possibly
many more.

However, if you can do the repair yourself, the equation changes dramatically
as your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free.  The educational aspects may also be
appealing.  You will learn a lot in the process.  Many problems can be
solved quickly and inexpensively.  Fixing an old vacuum cleaner to keep
in the rec room may just make sense after all.

This document provides maintenance and repair information for a large number
of small household appliances and portable power tools.  The repair of
consumer electronic equipment is dealt with by other documents in the
"Notes on the Troubleshooting and Repair of..." series.  Suggestions for
additions (and, of course, correction) are always welcome.

You will be able to diagnose problems and in most cases, correct them as
well.  Most problems with household appliances are either mechanical (e.g.,
dirt, lack of or gummed up lubrication, deteriorated rubber parts, broken
doohickies) or obvious electrical (e.g., broken or corroded connections,
short circuits, faulty heating elements) in nature.  With minor exceptions,
specific manufacturers and models will not be covered as there are so many
variations that such a treatment would require a huge and very detailed text.
Rather, the most common problems will be addressed and enough basic principles
of operation will be provided to enable you to narrow the problem down and
likely determine a course of action for repair.  In many cases, you will
be able to do what is required for a fraction of the cost that would be
charged by a repair center - or - be able to revive something that would
otherwise have gone into the dumpster - or remained in that closet until
you moved out of your house (or longer)!

Since so many appliances are variations on a theme - heating, blowing,
sucking, rotating, etc. - it is likely that even if your exact device does
not have a section here, a very similar one does.  Furthermore, with your
understanding of the basic principles of operation, you should be able to
identify what is common and utilize info in other sections to complete a

Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair (recommended), alt.home.repair,
or misc.consumers.house.  It will also be easier to do further research using
a repair textbook.  In any case, you will have the satisfaction of knowing you
did as much as you could before finally giving up or (if it is worthwhile
cost-wise) taking it in for professional repair.  With your newly gathered
knowledge, you will have the upper hand and will not easily be snowed by a
dishonest or incompetent technician.

Chapter 3) Some Tidbits

You may not realize the following:

* Virtually any table lamp can be restored to a like-new condition
  electrically for less than $5 in parts.

* The cause of a vacuum cleaner that starts blowing instead of sucking
  is likely a dirt clog somewhere.  It is virtually impossible for the
  motor to spin in the wrong direction and even if it did, the vacuum
  would still have some suction due to the type of blower that is commonly

* Many diagnoses of burned out motors are incorrect.  Very often motor
  problems are actually something else - and minor.  A truly burned out
  motor will often have died spectacularly and under adverse conditions.
  It will likely be smelly, charred, or may have created lots of sparks,
  tripped a circuit breaker or blew a fuse.  A motor that just stopped
  working may be due to worn (carbon) brushes, dirt, or a fault elsewhere
  in the appliance like a bad connection or switch or circuit - or the AC
  outlet might be bad.

* Fluorescent lamps use only 1/3 to 1/2 of the power of an incandescent lamp
  of similar light output.  With all the lighting used in an average household,
  this can add up particularly for high power ceiling fixtures.  However,
  fluorescent light color and quality may not be as aesthetically pleasing
  and fixtures or lamps may produce Radio Frequency Interference (RFI) causing
  problems with TV or radio reception.  Dimmers can usually not be used
  unless they are specifically designed for fluorescent fixtures.  Compact
  fluorescent lamps do indeed save energy but they can break just like any
  other light bulb!

* The initial inrush current to an incandescent bulb may be 10 times the
  operating current.  This is hard on switches and dimmers and is part of
  the reason behind why bulbs tend to burn out when switched on and not
  while just sitting there providing illumination.  Furthermore, an erratic
  switch or loose connection can shorten the life of an incandescent bulb
  due to repeated thermal shock.  And, these are not due to short circuits
  but bad intermittent connections.  True short circuits are less common
  and should result in a blown fuse or tripped circuit breaker.

* Bulb Savers and other devices claiming to extend the life of incandescent
  light bulbs may work but do so mostly by reducing power to the bulb at the
  expense of some decrease in light output and reduced efficiency.  It is
  estimated that soft start alone (without the usual associated reduction in
  power) does not prolong the life of a typical bulb by more than a few hours.

  Thus, in the end, these device increase costs if you need to use more or
  larger bulbs to make up for the reduced light output.  The major life cycle
  expense for incandescent lighting is not the cost of the bulbs but the cost
  of the electricity - by a factor of 25 to 50!  For example, it costs about
  $10 in electricity to run a 100 W bulb costing 25 cents over the course of
  its 1000 hour life.  However, these devices (or the use of 130 V bulbs) may
  make sense for use in hard-to-reach locations.  Better yet, consider compact
  or normal fluorescent bulbs or fixtures which last much longer and are much
  more efficient than incandescents (including halogen).

* Smart bulbs are legitimate technology with built in automatic off, dimmers,
  blink capability, and other 'wizzy' features but they burn out and break just
  like ordinary bulbs.  Thus, it hardly makes sense to spend $5 to $10 for
  something that will last 1000 to 1500 hours.  Install a proper dimmer,
  automatic switch, or external blinker instead.

* A Ground Fault Circuit Interrupter (GFCI) protects people against shock
  but does not necessarily protect appliances from damage due to electrical
  faults.  This is the function of fuses, circuit breakers, and thermal
  protectors. A GFCI *can* generally be installed in place of a 2-wire
  ungrounded outlet to protect it and any outlets downstream.  Check your
  local electrical Code to be sure if this is permitted.

* Don't waste your money on products like the 'Green Plug', magnetic water
  softeners, whole house TV antennas that plug into the wall socket, and
  other items of the "it sounds too good to be true' variety.  These are very
  effective only at transferring money out of your wallet but rarely work as

  - The Green Plug will not achieve anywhere near the claimed savings and may
    actually damage or destroy certain types of appliances like, guess what?:
    refrigerators and other induction motor loads.  Ever seen the demo?

    The Green Plug is supposed to reduce reactive power (V and I out of phase
    due to inductive or capacitive loads) but residential users don't pay for
    reactive power anyway, only the real power they use.  In addition, this is
    a minor concern for modern appliances.

    The demo you see in the store that shows a utility meter slowing down
    substantially when the Green Plug is put in the circuit is bogus for two
    reasons: (1) The motor being powered is totally unloaded resulting in a
    high ratio of reactive to real power.  Under normal use with a motor
    driving a load, the reduction in electricity use would be negligible.
    (2) The meter is wired to include reactive power in its measurement which,
    as noted above, is not the case with residential customers.

  - Magnetic and radio frequency water softeners are scams - pure and simple.
    They cloak absolutely useless technology in so much 'technobabble' that
    even Ph.D. scientists and engineers have trouble sorting it all out.
    The latest wrinkle adds advanced microprocessor control optimized for
    each potential mineral deposit.  Yeh, sure.

    Mention the word 'magnetism' and somehow, people will pay $300 for $2
    worth of magnets that do nothing - and then be utterly convinced of their
    effectiveness.  They forget that perhaps the instruction manual suggested
    changes in their water use habits - which was the true reason for any
    improvement.  Perhaps the magnets can be used to stick papers on the
    refrigerator once you discover they don't do anything for the water.

    BTW, the same goes for magnetic wine flavor enhancers :-).

  - Whole house TV antennas are great for picking up signals with ghosts,
    noise, and other distorting effects.  The premise that 'more is better'
    is fundamentally flawed when it comes to TV reception.  In rare cases
    they may produce a marginally viewable picture in an otherwise unfavorable
    location but these are the exceptions.  A pair of set-top rabbit ears will
    generally be superior.

  I will be happy to revise these comments if someone can provide the results
  of evaluations of any of these devices conducted by a recognized independent
  testing laboratory.  However, I won't hold my breath waiting.

Chapter 4) Basic Appliance Theory

  4.1) What is inside an appliance?

There isn't much rocket science in the typical small appliance (though that
is changing to some extent with the use of microcomputer and fuzzy logic
control).  Everything represents variations on a relatively small number
of basic themes:

* Heating - a resistance element similar to what you can see inside a
  toaster provides heat to air, liquids, or solids by convections,
  conduction, or direct radiant (IR) heat.

* Rotation, blowing, sucking - a motor provides power to move air as in
  a fan or vacuum cleaner, water as in a sump pump, or provide drive as
  in an electric pencil sharpener, food mixer, or floor polisher.

* Control - switches and selectors, thermostats and speed regulators,
  and microcomputers determine what happens, when, how much, and assure
  safe operation.

  4.2) Basic electrical principles

Relax! This is not going to be a tutorial on computer design.  Appliances
are simple devices.  It is possible to repair many appliance faults without
any knowledge beyond 'a broken wire is probably a problem' or 'this part
is probably bad because it is charred and broken in half'.  However, a
very basic understanding of electrical principles will enable you to more
fully understand what you are doing.  Don't worry, there will be no heavy
math.  The most complicated equations will be variations on Ohm's law:
V=I*R and P=V*V/R.

  4.3) Voltage, current, and resistance

If you have any sort of background in electricity or electronics, then
you can probably skip the following introductory description - or have
some laughs at my expense.

The easiest way to explain basic electrical theory without serious math
is with a hydraulic analogy.  This is of the plumbing system in your house:

Water is supplied by a pipe in the street from the municipal water company
or by a ground water pump.  The water has a certain pressure trying to
push it through your pipes.  With electric circuits, voltage is the analog
to pressure.  Current is analogous to flow rate.  Resistance is analogous
the difficulty in overcoming narrow or obstructed pipes or partially open

Intuitively, then, the higher the voltage (pressure), the higher the
current (flow rate).   Increase the resistance (partially close a valve or
use a narrower pipe) and for a fixed voltage (constant pressure), the
current (flow rate) will decrease.

With electricity, this relationship is what is known as linear: double the
voltage and all other factors remaining unchanged, the current will double
as well.  Increase it by a factor of 3 and the current will triple.  Halve
the resistance and for a constant voltage source, the current will double.
(For you who are hydraulic engineers, this is not quite true with plumbing
as turbulent flow sets in, but this is just an analogy, so bear with me.)

Note: for the following 4 items whether the source is Direct Current (DC)
such as a battery or Alternating Current (AC) from a wall outlet does not
matter.  The differences between DC and AC will be explained later.

The simplest electrical circuit will consist of several electrical
components in series - the current must flow through all of them to flow
through any of them.  Think of a string of Christmas lights - if one burns
out, they all go out because the electricity cannot pass through the broken
filament in the burned out bulb.

Note the term 'circuit'.  A circuit is a complete loop.  In order for
electricity to flow, a complete circuit is needed.

                          Switch (3)
               _____________/ ______________
              |                             |
              | (1)                         | (4)
      +-------+--------+                +---+----+
      |  Power Source  |                |  Load  |
      +-------+--------+                +---+----+
              |            Wiring (2)       |
1. Power source - a battery, generator, or wall outlet.  The hydraulic
   equivalent is a pump or dam (which is like a storage battery).  The
   water supply pipe in the street is actually only 'wiring' (analogous
   to the electric company's distribution system) from the water company's
   reservoir and pumps.

2. Conductors - the wiring.  Similar to pipes and aqueducts.  Electricity
   flows easily in good conductors like copper and aluminum.  These are like
   the insides of pipes.  To prevent electricity from escaping, an insulator
   like plastic or rubber is used to cover the wires.  Air is a pretty
   good insulator and is used with high power wiring such as the power
   company's high voltage lines but plastic and rubber are much more
   convenient as they allow wires to be bundled closely together.

3. Switch - turns current on or off.  These are similar to valves which
   do not have intermediate positions, just on and off.  A switch is not
   actually required in a basic circuit but will almost always be present.

4. Load - a light bulb, resistance heater, motor, solenoid, etc.  In
   true hydraulic systems such as used to control the flight surfaces of
   an aircraft, there are hydraulic motors and actuators, for example.

   With household water we usually don't think of the load.

Here are 3 of the simplest appliances:

* Flashlight: battery (1), case and wiring (2), switch (3), light bulb (4).

* Table lamp: wall outlet (1), line cord and internal wiring (2), power
  switch (3), light bulb (4).

* Electric fan, vacuum cleaner, garbage disposer: wall outlet (1), line
  cord and internal wiring (2), power switch (3), motor (4).

Now we can add some simple control devices:

5. Thermostat - a switch that is sensitive to temperature.  This is like an
   automatic water valve which shuts off if a set temperature is exceeded.
   Most thermostats are designed to open the circuit when a fixed or variable
   temperature is exceeded.  However, airconditioners, refrigerators, and
   freezers do the opposite - the thermostat switches on when the temperature
   goes too high.  Some are there only to protect against a failure elsewhere
   due to a bad part or improper use that would allow the temperature to
   go too high and start a fire.  Others are adjustable by the user and
   provide the ability to control the temperature of the appliance.

With the addition of a thermostat, many more appliances can be constructed
including (this is a small subset):

* Electric space heater (radiant), broiler, waffle iron: wall outlet (1),
  line cord and internal wiring (2), power switch (3) and/or thermostat (5),
  load (heavy duty heating element).

* Electric heater (convection), hair dryer: wall outlet (1), line cord
  and internal wiring (2), power switch (3) and/or thermostat (5), loads (4)
  (heating element and motor).

Electric heaters and cooking appliances usually have adjustable thermostats.

Hair dryers may simply have several settings which adjust heater power and
fan speed (we will get into how later).  The thermostat may be fixed and
to protect against excessive temperatures only.

That's it!  You now understand the basic operating principle of nearly all
small appliances.  Most are simply variations (though some may be quite
complex) on these basic themes.  Everything else is just details.

For example, a blender with 38 speeds just has a set of buttons (switches)
to select various combinations of motor windings and other parts to give
you complete control (as if you need 38 speeds!).  Toasters have a timer
or thermostat activate a solenoid (electromagnet) to pop your bread at
(hopefully) the right time.

5. Resistances - both unavoidable and functional.  Except for superconductors,
   all materials have resistance.  Metals like copper, aluminum, silver, and
   gold have low resistance - they are good conductors.  Many other metals
   like iron or steel are fair but not quite as good as these four.  One,
   NiChrome - an alloy of nickel and chromium - is used for heating elements
   because it does not deteriorate (oxidize) in air even at relatively high

   A significant amount of the power the electric company produces is lost
   to heating of the transmission lines due to resistance and heating.

   However, in an electric heater, this is put to good use.  In a flashlight
   or table lamp, the resistance inside the light bulb gets so hot that it
   provides a useful amount of light.

   A bad connection or overloaded extension cord, on the other hand, may
   become excessively hot and start a fire.

The following is more advanced - save for later if you like.

6. Capacitors - energy storage devices.  These are like water storage tanks
   (and similar is some ways to rechargeable batteries).

   Capacitors are not that common in small appliances but may be used with
   some types of motors and in RFI - Radio Frequency Interference - filters
   as capacitors can buffer - bypass - interference to ground.  The energy
   to power an electronic flash unit is stored in a capacitor, for example.
   Because they act like reservoirs - buffers - capacitors are found in the
   power supplies of most electronic equipment to smooth out the various
   DC voltages required for each device.

7. Inductors - their actual behavior is like the mass of water as it flows.
   Turn off a water faucet suddenly and you are likely to hear the pipes
   banging or vibrating.  This is due to the inertia of the water - it tends
   to want to keep moving.  Electricity doesn't have inertia but when wires
   are wound into tight coils, the magnetic field generated by electric
   current is concentrated and tends to result in a similar effect.  Current
   tends to want to continue to flow where inductance is present.

   The windings of motors and transformers have significant inductance but
   the use of additional inductance devices is rare in home appliances
   except for RFI - since inductance tends to prevent current from changing,
   it can also be used to prevent interference from getting in or out.

8. Controls - rheostats and potentiometers allow variable control of current
   or voltage.  A water faucet is like a variable resistor which can be
   varied from near 0 ohms (when on fully) to infinite ohms (when off).

  4.4) Ohm's Law

The relationships that govern the flow of current in basic circuits (without
capacitance or inductance - which is the case with many appliances) are
contained in a very simple set of equations known an Ohm's Law.

The simplest of these are:

                    V = I * R (1)
                    I = V / R (2) 
                    R = V / I (3)


     V is Voltage in Volts (or millivolts - mV or kilovolts - KV).
     I is current in amperes (A) or milliamps (mA) 
     R is resistance in Ohms (ohms), kilo-Ohms (K Ohms), or mega-Ohms (M Ohms).

Power in watts (W) is equal to voltage times current in a resistive circuit
(no capacitance or inductance).  Therefore, rearranging the equations above,
we also obtain:

                    P = V * I      (4)
                    P = V * V / R  (5)
                    P = I * I * R  (6)

For example:

* For a flashlight with a pair of Alkaline batteries (3 V) and a light bulb
  with a resistance of 10 ohms, we can use (2) to find that the current
  is I = (3 V) / (10 ohms) = .3 A.  The from (4) we find that the power
  is: P = (3 V * .3 A) = .9 W.

* For a blow-dryer rated at 1000 W, the current drawn from a 120 V line
  would be: I = P / V (by rearranging (4) = 1000 W / 120 V = 8.33 A.

As noted above:

* Increase voltage -> higher current.  (If the water company increases the
  pressure, your shower used more water in a given time.)

* Decrease resistance -> higher current.  (You have a new wider pipe installed
  between the street and your house.  Or, you open the shower valve wider.)

(Note that the common use of the term 'water pressure' is actually not
correct.  The most likely cause of what is normally described as low
water pressure is actually high resistance in the piping between your
residence and the street.  There is a pressure drop in this piping just
as there would be a voltage drop across a high value resistor.)

  4.5) DC and AC

While electricity can vary in any way imaginable, the most common forms
for providing power are direct current and alternating current:

A direct current source is at a constant voltage.  Displaying the voltage
versus time plot for such a source would show a flat line at a constant
level.  Some examples:

  * Alkaline AA battery - 1.5 V (when new).
  * Automotive battery - 12 V (fully charged).
  * Camcorder battery - 7.2 V (charged).
  * Discman AC adapter - 9 VDC (fully loaded).
  * Electric knife AC adapter - 3.6 VDC.

An Alternating Current (AC) source provides a voltage that is varying
periodically usually at 60 Hz (U.S.) or 50 Hz (many other countries).
Note that 1 Hz = 1 cycle per second.  Therefore, a 60 Hz AC voltage
goes through 60 complete cycles in each second.  For power, the shape
of the voltage is a sinusoid which is the smoothest way that anything
can vary periodically between two levels.

The nominal voltage from an AC outlet in the U.S. is around 115 VAC.  This
is the RMS (Root Mean Square) value, not the peak (0 to maximum).  In simple
terms, the RMS value of an AC voltage and the same value of a DC voltage
will result in identical heating (power) to a resistive load.  For example,
115 VAC RMS will result in the same heat output of a broiler as 115 VDC.

Direct current is used for many small motor driven appliances particularly
when battery power is an option since changing DC into AC requires some
additional circuitry.  All electronic equipment require various DC voltages
for their operation.  Even when plugged into an AC outlet, the first thing
that is done internally (or in the AC adapter in many cases) is to convert
the AC to various DC voltages.

The beauty of AC is that a very simple device - a transformer - can
convert one voltage into another.  This is essential to long distance
power distribution where a high voltage and low current is desirable to
minimize power loss (since it depends on the current).  You can see
transformers atop the power poles in your neighborhood reducing the
2,000 VAC or so from a local distribution transformer to your 115 VAC
(actually, 115-0-115 were the total will be used by large appliances like
electric ranges and clothes dryers).  That 2,000 VAC was stepped down
by a larger transformer from around 12,000 VAC provided by the local
substation.  This, in turn, was stepped down from the 230,000 VAC or
more used for long distance electricity transmission.  Some long distance
lines are over 1,000,000 volts (MV).

When converting between one voltage and another with a transformer, the
amount of current (amps) changes in the inverse ratio.  So, using 230 KV
for long distance power transmission results in far fewer heating losses
as the current flow is reduced by a factor of 2,000 over what it would
be if the voltage was only 115 V, for example.  Recall that power loss
from P=I*I*R is proportional to the square of the current and thus in
this example is reduced by a factor of 4,000,000!

Many small appliances include power transformers to reduce the 115 VAC
to various lower voltages used by motors or or electrical components.
Common AC adapters - often simply called transformers or wall warts -
include a small transformer as well.  Where their output is AC, this
is the only internal component other than a fuse or thermal fuse for
protection.  Where their output is DC, additional components convert
the low voltage AC from the transformer to DC and a capacitor smoothes
it out.

  4.6) Series and parallel circuits

Up until now, we have been dealing with the series circuit - all parts
are in a single line from power source, wiring, switches, load, and
anything else.  In a series circuit, the current must be the same
through all components.  The light bulb and switch in a flashlight
pass exactly the same value of amperes.  If there were two light bulbs
instead of one and they were connected in series - as in a Christmas
tree light set - then the current must be equal in all the bulbs but
the voltages across each one would be reduced.

The loads, say resistance heating elements, are now drawn with the
schematic symbol (as best as can be done using ASCII) for a resistor.

               _____________/ __________________
              |                 I -->           |
              |                        ^    ^   |
              |                        |    |   / R1
              |                        |   V1   \ Load 1
      +-------+--------+               |    |   /
      |  Power Source  |                    v__ |
      +-------+--------+              V(S)  ^   |
              |                             |   / R2
              |                        |   V2   \ Load 2
              |                        |    |   /
              |                        v    v   |

The total resistance, R(T), of the resistors in this series circuit is:

                    R(T) = R1 + R2                (7)

The voltage across each of the resistors would be given by:

                    V1 = V(S) * R1 / (R1 + R2)    (8)
                    V2 = V(S) * R2 / (R1 + R2)    (9)

The current is given by:

                    I = V(S)  / (R1 + R2)        (10)

However, another basic configuration, is also possible.  With a parallel
circuit, components are connected not one after the other but next to
one another as shown below:

               _____________/ ___________________________
              |                      I -->  |            |
              |                 ^           |            |
      +-------+--------+        |           / R1         / R2
      |  Power Source  |       V(S)         \ Load 1     \ Load 2
      +-------+--------+        |           /            /
              |                 v           |v I(1)      |v I(2)

Now, the voltages across each of the loads is necessarily equal but the
individual currents divide according to the relative resistances of each

The total resistance, R(T), of the parallel resistors in this circuit is:

                    R(T) = (R1 * R2) / (R1 + R2)  (11)

The currents through each of the loads would be given by:

                    I1 = V(S)/R1                  (12)
                    I2 = V(S)/R2                  (13)

The total current is given by:

                    I = I1 + I2                   (14)

Many variations on these basic arrangements are possible but nearly all can
be reduced systematically to a combination of series or parallel circuits.

Chapter 5) Appliance Troubleshooting

  5.1) SAFETY

Appliances run on either AC line power or batteries.  In the latter case,
there is little danger to you except possibly from burns due to short circuits
and heating effect or irritation from the caustic chemicals from old leaky

However, AC line power can be lethal.  Proper safety procedures must be
followed whenever working on live equipment (as well as devices which may
have high energy storage capacitors like TVs, monitors, and microwave
ovens).  AC line power due to its potentially very high current is actually
considerably more dangerous than the 30 KV found in a large screen
color TV!

These guidelines are to protect you from potentially deadly electrical shock
hazards as well as the equipment from accidental damage.

Note that the danger to you is not only in your body providing a conducting
path, particularly through your heart.  Any involuntary muscle contractions
caused by a shock, while perhaps harmless in themselves, may cause collateral
damage - there are many sharp edges inside this type of equipment as well as
other electrically live parts you may contact accidentally.

  5.2) Safety myths

For nearly all the appliances we will be covering, there is absolutely
no danger of electrical shock once the unit is unplugged from the wall
socket (not, however, just turned off, but unplugged).

You may have heard warnings about dangers from unplugged appliances.
Perhaps, these were passed down from your great great grandparents or
from local bar room conversation.

Except for devices with large high voltage capacitors connected to the
line or elsewhere, there is nothing inside an appliance to store a
painful or dangerous charge.  Even these situations are only present
in microwave ovens, fluorescent lamps and fixtures with electronic
ballasts, universal power packs for camcorders or portable computers,
or appliances with large motors.  Other than these, once an appliance
is unplugged all parts are safe to touch - electrically that is.  There
may still be elements or metal brackets that are burning hot as metal
will tend to retain heat for quite a while in appliances like toasters
or waffle irons.  Just give them time to cool.  There are often many
sharp edges on sheetmetal as well.  Take your time and look before you
leap or grab anything.

  5.3) Safety guidelines

The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions.  Appliance repair can be
both rewarding and economical.  Just be sure that it is also safe!

* Don't work alone - in the event of an emergency another person's presence
  may be essential.

* Always keep one hand in your pocket when anywhere around a powered
  line-connected or high voltage system.

* Wear rubber bottom shoes or sneakers.

* Wear eye protection - large plastic lensed eyeglasses or safety goggles.

* Don't wear any jewelry or other articles that could accidentally contact
  circuitry and conduct current, or get caught in moving parts.

* Set up your work area away from possible grounds that you may accidentally

* Know your equipment: small appliances with 2 prong plugs do not use any
  part of the outside case for carrying current.  Any metal parts of the
  case will either be totally isolated or possibly connected to one side
  of the line through a very high value resistor and/or very low value
  capacitor.  However, there may be exceptions.  And, failures may occur.
  Appliances with 3 prong plugs will have the case and any exposed metal
  parts connected to the safety ground.

* If circuit boards or other subassemblies need to be removed from their
  mountings, put insulating material between them and anything they may
  short to.  Hold them in place with string or electrical tape.  Prop them
  up with insulation sticks - plastic or wood.

* Parts of heating appliances can get very hot very quickly.  Always carefully
  test before grabbing hold of something you will be sorry about later.

* If you need to probe, solder, or otherwise touch circuits with power off,
  discharge (across) large power supply filter capacitors with a 2 W or greater
  resistor of 100-500 ohms/V approximate value (e.g., for a 200 V capacitor
  use a 50 K ohm resistor).  The only places you are likely to find large
  capacitors in small appliance repair are in induction motor starting or
  running circuitry or the electronic ballasts of fluorescent fixtures.

* Connect/disconnect any test leads with the equipment unpowered and
  unplugged. Use clip leads or solder temporary wires to reach cramped
  locations or difficult to access locations.

* Perform as many tests as possible with the device unplugged.  Even with
  the power switch supposedly off, if the unit is plugged into a live outlet,
  line voltage may be present in unexpected places or probing may activate
  a motor due to accidentally pressing a microswitch.  Most parts in
  household appliances and power tools can be can be tested using only
  an ohmmeter or continuity checker.

* If you must probe live, put electrical tape over all but the last 1/16"
  of the test probes to avoid the possibility of an accidental short which
  could cause damage to various components.  Clip the reference end of the
  meter or scope to the appropriate ground return so that you need to only
  probe with one hand.

* Use an isolation transformer if there is any chance of contacting line
  connected circuits.  A Variac(tm) is not an isolation transformer!

  The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a
  good idea but will not protect you from shock from many points in a line
  connected TV or monitor, or the high voltage side of a microwave oven, for
  example.  (Note however, that, a GFCI may nuisance trip at power-on or at
  other random times due to leakage paths (like your scope probe ground) or
  the highly capacitive or inductive input characteristics of line powered
  equipment.)  A fuse or circuit breaker is too slow and insensitive to provide
  any protection for you or in many cases, your equipment.  However, these
  devices may save your scope probe ground wire should you accidentally connect
  it to a live chassis.

* Don't attempt repair work when you are tired.  Not only will you be more
  careless, but your primary diagnostic tool - deductive reasoning - will
  not be operating at full capacity.

* Finally, never assume anything without checking it out for yourself!
  Don't take shortcuts!

  5.4) Should I unplug appliances when not in use?

There is no hard and fast rule.  Personally, I do unplug heating appliances
when I am done with them.  The quality of internal construction is not always
that great and this is a minor annoyance to avoid a possible fire hazard
should something fail or should such an appliance accidentally be left on.

BTW, electronic equipment should always be unplugged during lightning
storms since it may be very susceptible to power surge and lightning
damage.  Don't forget the telephones and computer modems as well.
This is not as much of a problem with small appliances that do not
include electronic controllers as except for direct lightning strikes,
the power switch will provide protection.

  5.5) Troubleshooting tips

Many problems have simple solutions.  Don't immediately assume that
your problem is some combination of esoteric complex convoluted
failures.  For a dead appliance, the most likely cause might just be
a bad line cord or plug!  Try to remember that the problems with the most
catastrophic impact on operation (an appliance that blows fuses) usually
have the simplest causes (a wire shorting due to frayed insulation).

If you get stuck, sleep on it.  Sometimes, just letting the problem
bounce around in your head will lead to a different more successful
approach or solution.  Don't work when you are really tired - it is both
dangerous and mostly non-productive (or possibly destructive - especially
with AC line powered appliances).

Whenever working on precision equipment, make copious notes and diagrams.
Yes, I know, a toaster may not exactly be precision equipment, but trust me.
You will be eternally grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange
of cables, but not always.  Apparently identical screws may be of differing
lengths or have slightly different thread types.  Little parts may fit in
more than one place or orientation.  Etc.  Etc.

Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly.

Select a work area which is well lighted and where dropped parts can
be located - not on a deep pile shag rug.  Something like a large plastic
tray with a slight lip may come in handy as it prevents small parts from
rolling off of the work table.  The best location will also be relatively
dust free and allow you to suspend your troubleshooting to eat or sleep or
think without having to pile everything into a cardboard box to eat dinner.

  5.6) Basic hand tools

A basic set of precision hand tools will be all you need to work on
most appliances.  These do not need to be really expensive but poor quality
tools are worse than useless and can cause damage.  Stanley and Craftsman
tools are fine.  Needed tools include a selection of Philips and straight
blade screwdrivers, socket drivers, open end or adjustable wrenches of various
sizes, needlenose pliers, wire cutters, tweezers, and dental picks.

An electric drill or drill press with a set of small (1/16" to 1/4") high
quality high speed drill bits is handy for some types of restoration where
new holes need to be provided.  A set of machine screw taps is also useful
at times.

A medium power soldering iron and rosin core solder (never never use
acid core solder or the stuff for sweating copper pipes on electrical
or electronic repairs!) will be required if you need to make or replace any
soldered connections.  A soldering gun is desirable for any really beefy
soldering.  See the section: "Soldering techniques".

A crimping tool and an assortment of solderless connectors often called
'lugs' will be needed to replace damaged or melted terminals in small
appliances.  See the section: "Solderless connectors".

Old dead appliances can often be valuable sources of hardware and sometimes
even components like switches and heating elements.  While not advocating
being a pack rat, this does have its advantages at times.

  5.7) Soldering techniques

Soldering is a skill that is handy to know for many types of construction
and repair.  For modern small appliances, it is less important than it once
was as solderless connectors have virtually replaced solder for internal

However, there are times where soldering is more convenient.  Use of the
proper technique is critical to reliability and safety.  A good solder
connection is not just a bunch of wires and terminals with solder dribbled
over them.  When done correctly, the solder actually bonds to the surface
of the metal (usually copper) parts.

Effective soldering is by no means difficult but some practice may be needed
to perfect your technique.

The following guidelines will assure reliable solder joints:

* Only use rosin core solder (e.g., 60/40 tin/lead) for electronics work.
  A 1 pound spool will last a long time and costs about $10.  Suggested
  diameter is .030 to .060 inches for appliances.  The smaller size is
  preferred as it will be useful for other types of precision electronics
  repairs or construction as well.  The rosin is used as a flux to clean
  the metal surface to assure a secure bond.  NEVER use acid core solder
  or the stuff used to sweat copper pipes!  The flux is corrosive and
  it is not possible to adequately clean up the connections afterward to
  remove all residue.

* Keep the tip of the soldering iron or gun clean and tinned.  Buy tips that
  are permanently tinned - they are coated and will outlast countless normal
  copper tips.  A quick wipe on a wet sponge when hot and a bit of solder
  and they will be as good as new for a long time.  (These should never be
  filed or sanded).

* Make sure every part to be soldered - terminal, wire, component leads -
  is free of any surface film, insulation,  or oxidation.  Fine sandpaper or
  an Xacto knife may be used, for example, to clean the surfaces.  The secret
  to a good solder joint is to make sure everything is perfectly clean
  and shiny and not depend on the flux alone to accomplish this. Just make
  sure the scrapings are cleared away so they don't cause short circuits.

* Start with a strong mechanical joint.  Don't depend on the solder to
  hold the connection together.  If possible, loop each wire or component
  lead through the hole in the terminal.  If there is no hole, wrap them
  once around the terminal.  Gently anchor them with a pair of needlenose

* Use a properly sized soldering iron or gun: 20-25 W iron for fine circuit
  board work; 25-50 W iron for general soldering of terminals and wires
  and power circuit boards; 100-200 W soldering gun for chassis and large
  area circuit planes.  With a properly sized iron or gun, the task will be
  fast - 1 to 2 seconds for a typical connection - and will result in little
  or no damage to the circuit board, plastic switch housings, insulation,
  etc.  Large soldering jobs will take longer but no more than 5 to 10
  seconds for a large expanse of copper.  If it is taking too long, your
  iron is undersized for the task, is dirty, or has not reached operating
  temperature.  For appliance work there is no need for a fancy soldering
  station - a less than $10 soldering iron or $25 soldering gun as
  appropriate will be all that is required.

* Heat the parts to be soldered, not the solder.  Touch the end of the solder
  to the parts, not the soldering iron or gun.  Once the terminal, wires,
  or component leads are hot, the solder will flow via capillary action, fill
  all voids, and make a secure mechanical and electrical bond.  Sometimes,
  applying a little from each side will more effectively reach all nooks
  and crannies.

* Don't overdo it.  Only enough solder is needed to fill all voids.  The
  resulting surface should be concave between the wires and terminal, not
  bulging with excess solder.

* Keep everything absolutely still for the few seconds it takes the solder
  to solidify.  Otherwise, you will end up with a bad connection - what is
  called a 'cold solder joint'.

* A good solder connection will be quite shiny - not dull gray or granular.
  If your result is less than perfect reheat it and add a bit of new solder
  with flux to help it reflow.

Practice on some scrap wire and electronic parts.  It should take you about
3 minutes to master the technique!

  5.8) Desoldering techniques

Occasionally, it will be necessary to remove solder - either excess or
to replace wires or components.  A variety of tools are available for
this purpose.  The one I recommend is a vacuum solder pump called
'SoldaPullet' (about $20).  Cock the pump, heat the joint to be cleared,
and press the trigger.  Molten solder is sucked up into the barrel of the
device leaving the terminal nearly free of solder.  Then use a pair of
needlenose pliers and a dental pick to gently free the wires or component.
Other approaches that may be used in place of or in addition to this:
Solder Wick which is a copper braid that absorbs solder via capillary
action; rubber bulb type solder pumps, and motor driven vacuum solder
rework stations (pricey).

See the document: "Troubleshooting and Repair of Consumer Electronics Equipment" for additional info on desoldering of electronic components.

  5.9) Soldering pins in plastic connectors

The thermoplastic used to mold many common cheap connectors softens or
melts at relatively low temperatures.  This can result in the pins popping
out or shifting position (even shorting) as you attempt to solder to them
to replace a bad connection, for example.

One approach that works in some cases is to use the mating socket to stabilize
the pins so they remain in position as you solder.  The plastic will still
melt - not as much if you use an adequately sized iron since the socket will
act as a heat sink - but will not move.

An important consideration is using the proper soldering iron.  In some
cases, a larger iron is better - you get in and out more quickly without
heating up everything in the neighborhood.

  5.10) Solderless connectors

Most internal connections in small appliances are made using solderless
connectors.  These include twist on WireNuts(tm) and crimped terminal lugs
of various sizes and configurations.

WireNuts allow multiple wires to be joined by stripping the ends and then
'screwing' an insulated thimble shaped plastic nut onto the grouped ends
of the wires.  A coiled spring (usually) inside tightly grips the bare
wires and results in a mechanically and electrically secure joint.  For
appliance repair, the required WireNuts will almost always already be
present since they can usually be reused.  If you need to purchase any,
they come in various sizes depending on the number and size of the wires
that can be handled.  It is best to twist the individual conductor strands
of each wire together and then twist the wires together slightly before
applying the WireNut.

Crimped connectors, called lugs, are very common in small appliances.  One
reason is that it is easier, faster, and more reliable, to make connections
using these lugs with the proper crimping equipment than with solder.

A lug consists of a metal sleeve which gets crimped over one or more wires,
an insulating sleeve (usually, not all lugs have these), and a terminal
connection: ring, spade, or push-on are typical.

Lugs connect one or more wires to the fixed terminals found on switches,
motors, thermostats, and so forth.

There are several varieties:

* Ring lugs - the end looks like an 'O' and must be installed on a threaded
  terminal of similar size to the opening in the ring.  The screw or nut must
  be removed to replace a ring lug.

* Spade lugs - the end looks like a 'U' and must be installed on a threaded
  terminal of similar size to the opening in the spade.  These can be slipped
  on and off without entirely removing the screw or nut.

* Push-on lugs - called 'FastOns' by one manufacturer.  The push-on terminal
  makes a tight fit with a (usually) fixed 'flag'.  There may also be a latch
  involved but usually just a pressure fit keeps the connection secure.
  However, excessive heat over time may weaken these types of connections,
  resulting in increased resistance, additional heating, and a bad connection
  or melt-down.

The push-on variety are most common in small appliances.

In the factory, the lugs are installed on the wires with fancy expensive
equipment.  For replacements, an inexpensive crimping tool and an assortment
of lugs will suffice.  The crimping tool looks like a pair of long pliers
and usually combines a wire stripper and bolt cutter with the crimping
function.  It should cost about $6-10.

The crimping tool 'squashes' the metal sleeve around the stripped ends of the
wires to be joined.  A proper crimp will not come apart if an attempt is made
to pull the wires free - the wires will break somewhere else first.  It is
gas-tight - corrosion (within reason) will not affect the connection.

Crimping guidelines:

* Use the proper sized lug.  Both the end that accepts the wire(s) and the
  end that screws or pushes on must be sized correctly.  Easiest is to
  use a replacement that is identical to the original.  Where this is not
  possible, match up the wire size and terminal end as closely as possible.
  There will be a minimum and maximum total wire cross sectional area that
  is acceptable for each size.  Avoid the temptation to trim individual
  conductor strands from wires that will not fit - use a larger size lug.
  Although not really recommended, the bare wires can be doubled over to
  thicken them for use with a lug that is slightly oversize.

* For heating appliances, use only high temperature lugs.  This will assure
  that the connections do not degrade with repeated temperature cycles.
* Strip the wire(s) so that they fit into the lug with just a bit showing
  out the other (screw or push-on) end.  Too long and your risk interference
  with the terminals and/or shorting to other terminals.  Too short and it
  is possible that one or more wires will not be properly positioned, will
  not be properly crimped, and may pull out or make a poor connection.  The
  insulation of the wires should be within the insulating sleeve - there
  should be no bare wire showing behind the lug.

* Crimp securely but don't use so much force that the insulating sleeve
  or metal sleeve is severed.  Usually 1 or 2 crimps for the actual wire
  connection and 1 crimp to compress the insulating sleeve will be needed.

* Test the crimp when complete - there should be no detectable movement of
  the wires.  If there is, you didn't crimp hard enough or the lug is
  too large for your wires.

  5.11) Wire stripping

In order to make most connections, the plastic or other insulating covering
must be removed to expose the bare copper conductors inside.  The best
way to do this is with a proper wire stripper which is either adjustable
or has dedicated positions for each wire size.  It is extremely important
that the internal conductor (single wire or multiple strands) are undamaged.
Nicks or loss of some strands reduces the mechanical and electrical integrity
of the connection.  In particular, a seriously nicked wire may break off
at a later time - requiring an additional repair or resulting in a safety
hazard or additional damage.  The use of a proper wire stripper will greatly
minimize such potential problems.

A pen knife or Xacto knife can be used in a pinch but a wire stripper is
really much much easier.

  5.12) Attaching wires to screw terminals

Screw terminals are often seen in appliances.  In most cases, lugs are
used to attach one or more wires to each terminal and when properly done,
this usually is the best solution.  However, in most cases, you can attach
the wire(s) directly if a lug is not available:

1. The best mechanical arrangement is to put the wire under a machine screw
   or nut, lock washer, and flat washer.  However, you will often see just
   the screw or nut (as in a lamp switch or wall socket).  For most
   applications, this is satisfactory.

2. Avoid the temptation to put multiple wires around a single terminal
   unless you separate each one with a flat washer.

3. Strip enough of the wire to allow the bare wire to be wrapped once around
   the terminal.  To much and some will poke out and might short to something;
   too little and a firm mechanical joint and electrical connection may be

4. For multistranded wire, tightly twist the strands of stripped wire together
   in a clockwise direction as viewed from the wire end.

5. Wrap the stripped end of the wire **clockwise** around the terminal post
   (screw or stud) so that it will be fully covered by the screw head, nut,
   or flat washer.  This will insure that the wire is grabbed as the screw
   or nut is tightened.  A pair of small needlenose pliers may help.

6. Hold onto the wire to keep it from being sucked in as the screw or nut
   is tightened.  Don't overdo it - you don't need to sheer off the head
   of the screw to make a secure reliable connection.

7. Inspect the terminal connection: the bare wire should be fully covered
   by the head of the screw, nut, or flat washer.  Gently tug on the wire
   to confirm that it is securely fastened.

  5.13) Test equipment

Very little test equipment is needed for most household appliance repair.

First, start with some analytical thinking.  Many problems associated
with household appliances do not require a schematic.  Since the internal
wiring of many appliances is so simple, you will be able to create your
own by tracing the circuits in any case.  However, for more complex
appliances, a schematic may be useful as wires may run behind and under
other parts and the operation of some custom switches may not obvious.
The causes for the  majority of problems will be self evident once you gain
access to the interior - loose connections or broken wires, bad switches,
open heating element, worn motor brushes, dry bearings.  All you will need
are some basic hand tools, a circuit and continuity tester, light oil and
grease, and your powers of observation (and a little experience).  Your
built in senses and that stuff between your ears represents the most
important test equipment you have.

The following will be highly desirable for all but the most obvious problems:

1. Circuit tester (neon light) - This is used to test for AC power or confirm
   that it is off.  For safety, nothing can beat the simplicity of a neon
   tester.   Its use is foolproof as there are no mode settings or range
   selections to contend with.  Touch its two probes to a circuit and if it
   lights, there is power.  (This can also take the place of an Outlet
   tester but it is not as convenient (see below).  Cost: $2-$3.

2. Outlet tester (grounds and miswiring) - This will confirm that a 3 prong
   outlet is correctly wired with respect to Hot, Neutral, and Ground.  While
   not 100% assured of correct wiring if the test passes, the screwup would
   need to be quite spectacular.  This simple device instantly finds missing
   Grounds and interchanged Hot and Neutral - the most common wiring mistakes.
   Just plug it into an outlet and if the proper two neon light are lit at
   full brightness, the outlet is most likely wired correctly.  Cost: about $6.

   These are just a set of 3 neon bulbs+resistors across each pair of wires.
   If the correct bulbs light at full brightness - H-N, H-G - then the
   circuit is likely wired correctly.  If the H-G light is dim or out or
   if both the H-G and G-N are dim, then you have no ground.  If the N-G
   light is on and the H-G light is off, you have reversed H and N, etc.

   What it won't catch: Reversed N and G (unlikely unless someone really
   screwed up) and marginal connections (since the neon bulbs doesn't use much
   current).  It also won't distinguish between 110 VAC and 220 VAC circuits
   except that the neon bulbs will glow much brighter on 220 VAC but without
   a direct comparison, this could be missed.

   For something that appears to test for everything but next week's weather:

   (From: Bill Harnell (bharne@adss.on.ca)).

   Get an ECOS 7105 tester! (ECOS Electronics Corporation, Oak Park, Illinois,
   708-383-2505).  Not cheap, however.  It sold for $59.95 in 1985 when I
   purchased somewhere around 600 of them for use by our Customer Engineers
   for safety purposes!

   It tests for:

   Correct wiring, reversed polarity, open Ground, open Neutral, open Hot,
   Hot & Ground reversed, Hot on neutral, Hot unwired, other errors,
   over voltage (130 VAC+), under voltage (105 VAC-), Neutral to Ground short,
   Neutral to Ground reversal, Ground impedance test (2 Ohms or less ground
   impedance - in the equipment ground conductor).

   Their less expensive 7106 tester performs almost all of the above tests.

   FWIW, I have no interest in the ECOS Corporation of any kind. Am just a
   very happy customer.

3. Continuity tester (buzzer or light) - Since most problems with appliances
   boil down to broken connections, open heating elements, defective switches,
   shorted wires, and bad motor windings, a continuity tester is all that
   is needed for most troubleshooting.  A simple battery operated buzzer or
   light bulb quickly identifies problems.  If a connection is complete, the
   buzzer will sound or the light will come on.  Note that a dedicated
   continuity tester is preferred over a similar mode on a multimeter because
   it will operate only at very low resistance.  The buzzer on a multimeter
   sounds whenever the resistance is less than about 200 ohms - a virtual open
   circuit for much appliance wiring.

   A continuity tester can be constructed very easily from an Alkaline
   battery, light bulb or buzzer, some wire, and a set of test leads with
   probes.  All of these parts are available at Radio Shack.

                     AA, C, or D cell    1.5 V flashlight bulb or buzzer
                            +|  -             +------------------+
   Test probe 1  o-----------| |--------------|  Bulb or buzzer  |-------+ 
                             |                +------------------+       |
   Test probe 2  o-------------------------------------------------------+

   CAUTION: Do not use this simple continuity tester on electronic equipment
   as there is a slight possibility that the current provided by the battery
   will be too high and cause damage.  It is fine for most appliances.

4. GFCI tester - outlets installed in potentially wet or outdoor areas should
   be protected by a Ground Fault Circuit Interrupter (GFCI).  A GFCI is now
   required by the NEC (Code) in most such areas.  This tester will confirm
   that any outlets protected by a GFCI actually will trip the device if there
   is a fault.  It is useful for checking the GFCI (though the test button
   should do an adequate job of this on its own) as well as identifying or
   testing any outlets downstream of the GFCI for protection.

   Wire a 3 prong plug with a 15 K ohm 1 W resistor between H and G.  Insulate
   and label it!  This should trip a GFCI protected outlet as soon as it is
   plugged in since it will produce a fault current of about 7 mA.

   Note that this device will only work if there is an actual Safety Ground
   connection to the outlet being tested.  A GFCI retrofitted into a 2 wire
   installation without a Ground cannot be tested in this way since a GFCI
   does not create a Ground.  However, jumpering this rig between the H and
   and a suitable earth ground (e.g., a cold water in an all copper plumbing
   system) should trip the GFCI.  Therefore, first use an Outlet Tester
   (above) to confirm that there is a Safety Ground present.

   The test button works because it passes an additional current through the
   sense coil between Hot and Neutral tapped off the wiring at the line side
   of the GFCI and therefore doesn't depend on having a Ground.

5. Multimeter (VOM or DMM) - This is necessary for actually measuring
   voltages and resistances.  Almost any type will do - even the $14.95
   special from Sears.  Accuracy is not critical for household appliance
   repair but reliability is important - for your safety if no other
   reason.  It doesn't really matter whether it is a Digital MultiMeter (DMM)
   or analog Volt Ohm Meter (VOM).  A DMM may be a little more robust should
   you accidentally put it on an incorrect scale.  However, they both serve
   the same purpose.  A cheap DMM is also not necessarily more accurate than
   a VOM just because it has digits instead of a meter needle.  A good quality
   well insulated set of test leads and probes is essential.  What comes with
   inexpensive multimeters may be too thin or flimsy.  Replacements are
   available.  Cost: $15-$50 for a multimeter that is perfectly adequate for
   home appliance repair.

   Note: For testing of household electrical wiring, a VOM or DMM can indicate
   voltage between wires which is actually of no consequence.  This is due to
   the very high input resistance/impedance of the instrument.  The voltage
   would read zero with any sort of load.  See the section: "Phantom voltage measurements of electrical wiring".

Once you get into electronic troubleshooting, an oscilloscope, signal
generator, and other advanced (and expensive) test equipment will be useful.
For basic appliance repair, such equipment would just gather dust.

  5.14) Getting inside consumer electronic equipment

Yes, you will void the warranty, but you knew this already.

Appliance manufacturers seem to take great pride in being very mysterious
as to how to open their equipment.  Not always, but this is too common
to just be a coincidence.

A variety of techniques are used to secure the covers on consumer
electronic equipment:

1. Screws.  Yes, many still use this somewhat antiquated technique.
   Sometimes, there are even embossed arrows on the case indicating
   which screws need to be removed to get at the guts.  In addition to
   obvious screw holes, there may be some that are only accessible when a
   battery compartment is opened or a trim panel is popped off.

   These are almost always of the Philips variety though more and more
   appliances are using Torx or security Torx type screws.  Many of these
   are hybrid types - a slotted screwdriver may also work but the Philips
   or Torx is a whole lot more convenient.

   A precision jeweler's  screwdriver set including miniature Philips
   head drivers is a must for repair of miniature portable devices.

2. Hidden screws.  These will require prying up a plug or peeling off
   a decorative decal.  It will be obvious that you were tinkering - it
   is virtually impossible to put a decal back in an undetectable way.
   Sometimes the rubber feet can be pryed out revealing screw holes.  For
   a stick-on label, rubbing your finger over it may permit you to locate
   a hidden screw hole.  Just puncture the label to access the screw as this
   may be less messy then attempting to peel it off.

3. Snaps.  Look around the seam between the two halves.  You may (if you are
   lucky) see points at which gently (or forcibly) pressing with a screwdriver
   will unlock the covers.  Sometimes, just going around the seam with a butter
   knife will pop the cover at one location which will then reveal the
   locations of the other snaps.

4. Glue.  Or more likely, the plastic is fused together.  This is particularly
   common with AC adapters (wall warts).  In this case, I usually carefully
   go around the seam with a hacksaw blade taking extreme care not to go
   through and damage internal components.  Reassemble with plastic electrical

5. It isn't designed for repair.   Don't laugh.  I feel we will see more
   and more of this in our disposable society.  Some devices are totally
   potted in Epoxy and are 'throwaways'.  With others, the only way to open
   them non-destructively is from the inside.

Don't force anything unless you are sure there is no alternative - most
of the time, once you determine the method of fastening, covers will
come apart easily.  If they get hung up, there may be an undetected
screw or snap still in place.

When reinstalling the screws, first turn them in a counter-clockwise direction
with very slight pressure. You will feel them "click" as they fall into the
already formed threads.  Gently turn clockwise and see if they turn easily.
If they do not, you haven't hit the previously formed threads - try again.
Then just run them in as you normally would. You can always tell when you
have them into the formed threads because they turn very easily for nearly
the entire depth.  Otherwise, you will create new threads which will quickly
chew up the soft plastic.  Note: these are often high pitch screws - one turn
is more than one thread - and the threads are not all equal.

The most annoying (to be polite) situation is when after removing the
18 screws holding the case together (losing 3 of them entirely and mangling
the heads on 2 others), removing three subassemblies, and two other circuit
boards, you find that the adjustment you wanted was accessible through a
hole in the case just by partially peeling back a rubber hand grip! (It
has happened to me).

When reassembling the equipment make sure to route cables and other wiring
such that they will not get pinched or snagged and possibly broken or have
their insulation nicked or pierced and that they will not get caught in
moving parts.  This is particularly critical for AC line operated appliances
and those with motors to minimize fire and shock hazard and future damage
to the device itself.  Replace any cable ties that were cut or removed during
disassembly and add additional ones of your own if needed.  Some electrical
tape may sometimes come in handy to provide insulation insurance as well.
As long as it does not get in the way, additional layers of tape will not
hurt and can provide some added insurance against future problems.  I often
put a layer of electrical tape around connections joined with WireNuts(tm)
as well just to be sure that they will not come off or that any exposed wire
will not short to anything.

  5.15) Getting built up dust and dirt out of a equipment

This should be the first step in any inspection and cleaning procedure.

Appliances containing fans or blowers seem to be dust magnets - an incredible
amount of disgusting fluffy stuff can build up in a short time - even with
built-in filters.

Use a soft brush (like a new cheap paint brush) to remove as much dirt,
dust, and crud, as possible without disturbing anything excessively.  Some
gentle blowing (but no high pressure air) may be helpful in dislodged
hard to get at dirt - but wear a dust mask.

Don't use compressed air on intricate mechanisms, however, as it might
dislodge dirt and dust which may then settle on lubricated parts and 
contaminating them.  High pressure air could move oil or grease from where
it is to where it should not be.  If you are talking about a shop air
line, the pressure may be much much too high and there may be contaminants
as well.

A Q-tip (cotton swab) moistened with politically correct alcohol can be used
to remove dust and dirt from various hard to get at surfaces.

  5.16) Lubrication of appliances and electronic equipment

The short recommendation is: Don't add any oil or grease unless you are
positively sure it is needed.  Most parts are lubricated at the factory and do
not need any further lubrication over their lifetime.  Too much lubrication is
worse then too little.  It is easy to add a drop of oil but difficult and time
consuming to restore a tape deck that has taken a swim.

NEVER, ever, use WD40!  WD40 is not a good lubricant despite the claims on the
label.  Legend has it that the WD stands for Water Displacer - which is one of
the functions of WD40 when used to coat tools for rust prevention.  WD40 is
much too thin to do any good as a general lubricant and will quickly collect
dirt and dry up.  It is also quite flammable and a pretty good solvent - there
is no telling what will be affected by this.

A light machine oil like electric motor or sewing machine oil should be
used for gear or wheel shafts.  A plastic safe grease like silicone grease
or Molylube is suitable for gears, cams, or mechanical (piano key) type
mode selectors.  Never use oil or grease on electrical contacts.

One should also NOT use a detergent oil.  This includes most automotive
engine oils which also have multiple additives which are not needed and are
undesirable for non-internal combustion engine applications.

3-In-One(tm) isn't too bad if that is all you have on hand and the future of
the universe depends on your fan running smoothly.  However, for things that
don't get a lot of use, it may gum up over time.  I don't know whether it
actually decomposes or just the lighter fractions (of the 3) evaporate.

Unless the unit was not properly lubricated at the factory (which is quite
possible), don't add any unless your inspection reveals the specific need.
Sometimes you will find a dry bearing, motor, lever, or gear shaft.  If
possible, disassemble and clean out the old lubricant before adding fresh
oil or grease.

Note that in most cases, oil is for plain bearings (not ball or roller)
and pivots while grease is used on sliding parts and gear teeth.

In general, do not lubricate anything unless you know there is a need.
Never 'shotgun' a problem by lubricating everything in sight!  You might
as well literally use a shotgun on the equipment!

  5.17) Common appliance problems

Despite the wide variety of appliances and uses to which they are put,
the vast majority of problems are going to be covered in the following
short list:

1. Broken wiring inside cordset - internal breaks in the conductors of
   cordsets or other connecting cords caused by flexing, pulling, or
   other long term abuse.  This is one of the most common problem with
   vacuum cleaners which tend to be dragged around by their tails.

   Testing: If the problem is intermittent, (or even if it is not), plug
   the appliance in and turn it on.  Then try bending or pushing the wire
   toward the plug or appliance connector end to see if you can make the
   internal conductors touch at least momentarily.  Ii the cordset is
   removable, test between ends with a continuity checker or multimeter
   on the low ohms scale.  If it is not detachable, open the appliance to
   perform this test.

2. Bad internal connections - broken wires, corroded or loosened terminals.
   Wires may break from vibration, corrosion, poor manufacturing, as
   well as thermal fatigue.  The break may be in a heating element or
   other subassembly.  In many cases, failure will be total as in
   when one of the AC line connections falls off.  At other times,
   operation will be intermittent or erratic - or parts of the appliance
   will not function.  For example, with a blow dryer, the heating element
   could open up but the fan may continue to run properly.

   Testing: In many cases, a visual inspection with some careful flexing
   and prodding will reveal the location of the bad connection.  If it is
   an intermittent, this may need to be done with a well insulated stick
   while the appliance is on and running (or attempting to run).  When
   all else fails, the use of a continuity checker or multimeter on the
   low ohms scale can identify broken connections which are not obviously
   wires visibly broken in two.  For testing heating elements, use the
   multimeter as a continuity checker may not be sensitive enough since
   the element normally has some resistance.

3. Short circuits.  While much less frequent than broken or intermittent
   connections, two wires touching or contacting the metal case of an
   appliance happens all too often.  Partially, this is due to the shoddy
   manufacturing quality of many small appliances like toaster ovens.  These
   also have metal (mostly) cabinets and many metal interior parts with
   sharp edges which can readily eat through wire insulation due to repeated
   vibrations, heating and cooling cycles, and the like.  Many appliances
   are apparently designed by engineers (this is being generous) who do not
   have any idea of how to build or repair them.  Thus, final assembly, for
   example, must sometimes be done blind - the wires get stuffed in and covers
   fastened - which may end up nicking or pinching wires between sharp metal
   parts.  The appliance passes the final inspection and tests but fails down
   the road.

   A short circuit may develop with no operational problems - but the case
   of the appliance will be electrically 'hot'.  This is a dangerous situation.
   Large appliances with 3 wire plugs - plugged into a properly grounded 3 wire
   circuit - would then blow a fuse or trip a circuit breaker.  However, small
   appliances like toaster, broilers, irons, etc., have two wire plugs and
   will just set there with a live cabinet.

   Testing: Visually inspect for bare wires or wires with frayed or worn
   insulation touching metal parts, terminals they should not be connected
   to, or other wires.  Use a multimeter on the high ohms scale to check
   between both prongs of the AC plug and any exposed metal parts.  Try all
   positions of any power or selector switches.  Any resistance measurement
   less than 100K ohms or so is cause for concern - and further checking.
   Also test between internal terminals and wires that should not be connected

   Too many people like to blame everything from blown light bulbs to
   strange noises on short circuits.  A 'slight', slow, or marginal short
   circuit is extremely rare.  Most short circuits in electrical wiring
   between live and neutral or ground (as opposed to inside appliances
   where other paths are possible) will blow a fuse or trip a breaker.  Bad
   connections (grounds, neutral, live), on the other hand, are much much
   more common.

4. Worn, dirty, or broken switches or thermostat contacts.  These will
   result in erratic or no action when the switch is flipped or thermostat
   knob is turned.  In many cases, the part will feel bad - it won't have
   that 'click' it had when new or may be hard to turn or flip.  Often,
   however, operation will just be erratic - jiggling the switch or knob
   will make the motor or light go on or off, for example.

   Testing: Where there is a changed feel to the switch or thermostat with
   an associated operational problem, there is little doubt that the part
   is bad and must be replaced.  Where this is not the case, label the
   connections to the switch or thermostat and then remove the wires.  Use
   the continuity checker or ohmmeter across each set of contacts.  They
   should be 0 ohms or open depending on the position of the switch or knob
   and nothing in between.  In most cases, you should be able to obtain
   both readings.  The exception is with respect to thermostats where room
   temperature is off one end of their range.  Inability to make the contacts
   open or close (except as noted above) or erratic intermediate resistances
   which are affected by tapping or jiggling are a sure sign of a bad set of

5. Gummed up lubrication, or worn or dry bearings.  Most modern appliances
   with motors are supposedly lubricated for life.  Don't believe it!  Often,
   due to environmental conditions (dust, dirt, humidity) or just poor quality
   control during manufacture (they forgot the oil), a motor or fan bearing
   will gum up or become dry resulting in sluggish and/or noisy operation
   and overheating.  In extreme cases, the bearing may seize resulting in
   a totally stopped motor.  If not detected, this may result in a blown
   fuse (at the least) and possibly a burnt out motor from the overheating.

   Testing: If the appliance does not run but there is a hum (AC line
   operated appliances) or runs sluggishly or with less power than you 
   recall when new, lubrication problems are likely.  With the appliance
   unplugged, check for free rotation of the motor(s).  In general, the
   shaft sticking out of the motor itself should turn freely with very
   little resistance.  If it is difficult to turn, the motor bearings
   themselves may need attention or the mechanism attached to the motor
   may be filled with crud.  In most cases, a thorough cleaning to remove
   all the old dried up and contaminated oil or grease followed by relubing
   with similar oil or grease as appropriate will return the appliance to
   good health.  Don't skimp on the disassembly - total cleaning will be
   best.  Even the motor should be carefully removed and broken down to
   its component parts - end plates, rotor, stator, brushes (if any) in
   order to properly clean and lubricate its bearings.  See the appropriate
   section of the chapter: "Motors 101" for the motor type in your appliance.

6. Broken or worn drive belts or gears - rotating parts do not rotate
   or turn slowly or with little power even through the motor is revving
   its little head off.  When the brush drive belt in an upright vacuum
   cleaner breaks, the results are obvious and the broken belt often falls
   to the ground (to be eaten by the dog or mistaken for a mouse tail - Eeek!)
   However, there are often other belts inside appliances which will result
   in less obvious consequences when they loosen with age or fail completely.

   Testing: Except for the case of a vacuum cleaner where the belt is readily
   accessible, open the appliance (unplugged!).  A good rubber belt will be
   perfectly elastic and will return to its relaxed length instantly when
   stretched by 25 percent and let go.  It will not be cracked, shiny, hard,
   or brittle.  A V-type belt should be dry (no oil coating), undamaged (not
   cracked, brittle, or frayed), and tight (it should deflect 1/4" to 1/2"
   when pressed firmly halfway between the pulleys).

   Sometimes all that is needed is a thorough cleaning with soap and water
   to remove accumulated oil or grease.  However, replacement will be required
   for most of these symptoms.  Belts are readily available and an exact
   match is rarely essential.

7. Broken parts - plastic or metal castings, linkages, washers, and other
   'doodads' are often not constructed quite the way they used to be.  When
   any of these fail, they can bring a complicated appliance to its knees.
   Failure may be caused by normal wear and tear, improper use (you tried
   to vacuum nuts and bolts just like on TV), accidents (why was your 3
   year old using the toaster oven as a step stool?), or shoddy manufacturing.

   Testing: In many cases, the problem will be obvious.  Where it is not,
   some careful detective work - putting the various mechanisms through
   their paces - should reveal what is not functioning.  Although replacement
   parts may be available, you can be sure that their cost will be excessive
   and improvisation may ultimately be the best approach to repair.  See
   the section: "Fil's tips on improvised parts repair".

8. Insect damage.  Many appliance make inviting homes for all sort of multi-
   legged creatures.  Evidence of their visits or extended stays will be
   obvious including frayed insulation, short circuits caused by bodily
   fluids or entire bodies, remains of food and droppings.  Even the smallest
   ventilation hole can be a front door.

   The result may be any of the items listed in (1) to (7) above.  Once the
   actual contamination has been removed and the area cleaned thoroughly,
   inspect for damage and repair as needed.  If the appliance failed while
   powered, you may also have damage to wiring or electronic components due
   to any short circuits that were created by the intruders' activities.

Chapter 6) Types of Parts Found in Small Appliances

  6.1) So many, so few

While there are an almost unlimited variety of small appliances and power
tools, they are nearly all constructed from under two dozen basic types
of parts.  And, even with these, there is a lot of overlap.

The following types of parts are found in line powered appliances:

        * Cordsets - wire and plug.
        * Internal wiring - cables and connectors.
        * Switches - power, mode, or speed selection.
        * Relays - electrically activated switches for power or control.
        * Electrical overload protection devices - fuses and circuit breakers.
        * Thermal protection devices - thermal fuses and thermal switches.
        * Controls 1 - adjustable thermostats and humidistats.
        * Controls 2 - rheostats and potentiometers.
        * Interlocks - prevent operation with case or door open.
        * Light bulbs - incandescent and fluorescent.
        * Indicators - incandescent or neon light bulbs or LEDs.
        * Heating elements - NiChrome coils or ribbon, Calrod, Quartz.
        * Solenoids - small and large.
        * Small electronic components - resistors, capacitors, diodes.
        * Motors - universal, induction, DC, timing.
        * Fans and Blowers - bladed or centrifugal.
        * Bearings and bushings.
        * Mechanical controllers - timing motors and cam switches.
        * Electronic controllers - simple delay or microprocessor based.

Battery and AC adapter powered appliance use most of the same types of
parts but they tend to be smaller and lower power than their line powered
counterparts.  For example, motors in line powered devices tend to be
larger, more powerful, and of different design (universal or induction
compared to permanent magnet DC type).  So, we add the following:

        * Batteries - Alkaline, Lithium, Nickel-Cadmium, Lead-acid.
        * AC adapters and chargers - wall 'warts' with AC or DC outputs.

The only major category of devices that these parts do not cover are gas
discharge lamps and lighting fixtures (fluorescent, neon, mercury, and
sodium), which we will discuss in a separate chapters.

  6.2) Cordsets - wire and plug

A 'cordset' is a combination of the cord consisting of 2 or 3 insulated wires
and a plug with 2 or 3 prongs.  Cord length varies from 12 inches (or less)
for some appliances like toasters to 25 feet or more for vacuum cleaners.
Most common length is 6-8 feet.  The size of the wire and type of insulation
also are important in matching a replacement cordset to an appliance.

Most plug-in appliances in the U.S. will have one of 3 types of line cord/plug

1. Non-polarized 2 prong.  The 2 prongs are of equal width so the plug
   may be inserted in either direction.  These are almost universal
   on older appliances but may be found on modern appliances as well 
   which are double insulated or where polarity does not matter.  (Note:
   it **must** not matter for user safety in any case.  The only time it can
   matter otherwise is with respect to (1) possible RFI (Radio Frequency
   Interference) generation or (2) service safety (this would put the
   center contact of a light bulb socket or internal switch and fuse on
   the Hot wire).

2. Polarized 2 prong.  The prong that is supposed to be plugged into
   the Neutral slot of the outlet is wider.  All outlets since sometime
   around the 1950s (???) have been constructed to accept polarized plugs
   only one way.  While no appliance should ever be designed where the
   way it is plugged in can result in a user safety hazard, a lamp socket
   where the shell - the screw thread part - is plugged into Neutral is
   less hazardous when changing a light bulb.  In addition, when servicing
   a small appliance with the cover removed, the Hot wire with a polarized
   plug should go to the switch and fuse and thus most of the circuitry will
   be disconnected with the switch off or fuse pulled.

3. Grounded 3 prong.  In addition to Hot and Neutral, a third grounding
   prong is provided to connect the case of the equipment to safety Ground.
   This provides added protection should internal wiring accidentally short
   to a user accessible metal cabinet or control.  In this situation, the
   short circuit will (or is supposed to) blow a fuse or trip a circuit
   breaker or GFCI rather than present a shock hazard.  DO NOT just cut
   off the third prong if your outlet does not have a hole for it.  Have
   the outlet replaced with a properly grounded one (which may require
   pulling a new wire from the service panel).  As a short term solution,
   the use of a '3 to 2' prong adapter is acceptable IF AND ONLY IF the
   outlet box is securely connected to safety Ground already (BX or Romex
   cable with ground).  Grounding also is essential for surge suppressors
   to operate properly (to the extent that they ever do) and may reduce
   RFI susceptibility and emissions if line filters are included (as with
   computer equipment and consumer electronics).  Power conditioners require
   the Ground connection for line filtering as well.

Each of these may be light duty (less than 5 Amps or 600 Watts), medium
duty (8 A or 1000 W) or heavy duty (up to 15 A or 1800 W).  The rating is
usually required to be stamped on the cord itself or on a label attached
to the cord.  Thickness of the cord is not a reliable indication of its
power rating!  (Note: U.S. 115 VAC 15 amp circuits are assumed throughout
this document unless otherwise noted.)

Light duty cordsets are acceptable for most appliances without high power
heating elements or heavy duty electric motors.  These include table lamps,
TVs, VCRs, stereo components, computers, dot matrix and inkjet printers,
thermal fax machines, monitors, fans, can openers, etc.  Electric blankets,
heating pads, electric brooms, and food mixers are also low power and light
duty cordsets are acceptable.  The internal wires used is #18 AWG which is
the minimum acceptable wire size (highest AWG number) for any AC line powered

Medium or heavy duty cordsets are REQUIRED for heating appliances like
electric heaters (both radiant and convection), toasters, broilers, steam and
dry irons, coffee makers and electric kettles, microwave and convection ovens,
laser printers, photocopiers, Xerographic based fax machines, canister and
upright vacuum cleaners and shop vacs, floor polishers, many portable and
most stationary power tools.  The internal wires used will be #16 AWG (medium
duty) or #14 AWG (heavy duty).

For replacement, always check the nameplate amps or wattage rating and use
a cordset which has a capacity at least equal to this.  The use of an
inadequate cordset represents a serious fire hazard.

Three prong grounded cordsets are required for most computer equipment,
heavy appliances, and anything which is not double insulated and has metal
parts that may be touched in normal operation (i.e., without disassembly).

The individual wires in all cordsets except for unpolarized types (e.g., lamp
cord) will be identified in some way.  For sheathed cables, color coding is
used.   Generally, in keeping with the NEC (Code), black will be Hot, white
will be Neutral, and green will be Safety Ground.  You may also find brown for
Hot, blue for Neutral, and green with a yellow stripe for Safety Ground.  This
is used internationally and is quite common for the cordsets of appliances and
electronic equipment.

For zip cord with a polarized plug, one of the wires will be tagged with with
a colored thread or a ridge on the outer insulation to indicate which is the
Hot wire.  For unpolarized types like lamp cord, no identification is needed
(though there still may be some) as the wires and prongs of the plug are

In general, when replacement is needed, use the same configuration and
length and a heavy duty type if the original was heavy duty.  Substituting
a heavy duty cordset for a light duty one is acceptable as long as the
additional stiffness is acceptable in terms of convenience.  A shorter
cord can usually be used if desired.  In most cases, a longer cord (within
reason) can be substituted as well.  However, performance of heavy duty
high current high wattage appliances may suffer if a really long cord (or
extension cord) is used voltage drop from the wire resistance.  For a modest
increase in length, use the next larger wire size (heavy duty instead of
medium duty, #14 instead of #16, for example).

Before disconnecting the old cord, label connections or make a diagram and
then match the color code or other wire identifying information.  In all cases,
it is best to confirm your final wiring with a continuity tester or multimeter
on the low ohms scale.  Mistakes on your part or the manufacturer of the new
cord are not unheard of!

Common problems: internal wiring conductors broken at flex points (appliance
or plug).  With yard tools, cutting the entire cord is common.  The connections
at the plug may corrode as well resulting in heating or a broken connection.

Testing: Appliance cordsets can always be tested with a continuity checker or
multimeter on a the low ohms scale.

* Squeeze, press, spindle, fold, mutilate the cord particularly at both ends
  as while testing to locate intermittent problems.

* If you are too lazy to open the appliance (or this requires the removal of
  29 screws), an induction type of tester such as used to locate breaks in
  Christmas tree light strings can be used to confirm continuity by plugging
  the cord in both ways and checked along its length to see if a point of
  discontinuity can be located.

  (From: Brian Symons (brians@mackay.net.au)).

  A permanent bench setup with a pair of outlets (one wired with reverse
  polarity marked: FOR TESTING ONLY) can be provided to facilitate connecting
  to either of the wires of the cordset when using an induction type tester.

Note: broken wires inside the cordset at either the plug or appliance end
are among the most common causes of a dead vacuum cleaner due to abuse
it gets - being tugged from the outlet, vacuum being dragged around by
the cord, etc.  Many other types of appliances suffer the same fate.
Therefore, checking the cord and plug should be the first step in
troubleshooting any dead appliance.

If the cord is broken at the plug end, the easiest thing to do is to
replace just the plug.  A wide variety of replacement plugs are available
of three basic types: clamp-on/insulation piercing, screw terminals,
and wire compression.

Clamp-on/insulation piercing plugs are installed as follows:  First, the
cord is cleanly cut but not stripped and inserted into the body of the
plug.  A lid or clamping bar is then closed which internally pierces the
insulation and makes contact with the prongs.  When used with the proper
size wire, these are fairly reliable for light duty use - table lamps
and other low power appliances.  However, they can lead to problems of
intermittent or bad connections if the wire insulation thickness does not
precisely match what the plug expects.

Plugs with screw terminals make a much more secure robust connections but
require a bit more time and care in assembly to assure a proper connection
and avoid stray wire strands causing short circuits or sticking out and
representing a shock hazard.  Tightly twist the strands of the stripped
wire together before wrapping around the screw in a clockwise direction
before tightening.  Don't forget to install the fiber insulator that is
usually supplied with the plug.

The best plugs have wire clamp terminals.  The stripped end of the wire
is inserted into a hole and a screw is tightened to clamp the wire in
place.  Usually, a molded plastic cover is then screwed over this assembly
and includes a strain relief as well.  These are nearly foolproof and
consequently are used in the most demanding industrial and medical
applications.  They are, not surprisingly, also typically the most

Where damage is present at the appliance end of the cord, it may be possible
to just cut off the bad portion and reinstall what remains inside of the
appliance.  As long as this is long enough and a means can be provided for
adequate strain relief, this is an acceptable alternative to replacement of
the entire cordset.

  6.3) Appliance cord gets hot

This applies to all high current appliances, not just space heaters though
these are most likely to be afflicted since they are likely to be run for
extended periods of time.

Of course, if the problem is with an *extension* cord, then either it is
overloaded or defective.  In either case, the solution should be obvious.

Some cords will run warm just by design (or cheapness in design using
undersized conductors).

However, if it is gets hot during use, this is a potential fire hazard.

If it is hot mainly at the plug end - get a heavy duty replacement plug - one
designed for high current appliances using screw terminals - at a hardware
store, home center, or electrical supply house.  Cut the cord back a couple
of inches.

If the entire cord gets warm, this is not unusual with a heater.  If it
gets hot, the entire cord should be replaced.  Sometimes with really old
appliance, the copper wires in the cord oxidize even through the rubber
insulation reducing their cross section and increasing resistance.  This
leads to excessive power dissipation in the cord.  Replacement *heavy duty*
cordsets are readily available.

  6.4) Extension cords

We treat extension cords too casually - abusing them and using underrated
extension cords with heavy duty appliances.  Both of these are serious
fire and shock hazards.  In addition, the use of a long inadequate
extension will result in reduced voltage due to resistive losses at the
far end.  The appliance may not work at full capacity and in some cases
may even be damaged by this reduced voltage.

Extension cord rules of use:

1. The capacity must be at least equal to the SUM of the wattages or amperages
   of all the appliances plugged in at the far end.  Larger is fine as well
   and is desirable for long extensions.  Check the rating marked on the cord
   or a label attached to the cord.  Thickness of the outside of the cord is
   not a reliable indication of power rating.

2. Use a type which is the most restrictive of any appliances that will be
   plugged in (e.g., 3 prong if any are of this type, 2 prong polarized
   otherwise unless your outlets are non-polarized (old dwellings).

3. Use only as long an extension as required.  For very long runs, use
   a higher capacity extension even if the power requirements are modest.

4. NEVER run extensions under carpeting as damage is likely and this will
   go undetected.  Never run extensions inside walls.  Add new outlets where
   needed with properly installed building wire (Romex).  This must be done
   in such a way that it meets the National Electric Code (NEC) in your area.
   It may need to be inspected if for no other reason than to guarantee that
   your homeowner's insurance won't give you a hard time should any 'problems'
   arise.  Surface mount outlets and conduit are available to extend the reach
   of existing outlets with minimal construction if adding new ones is
   difficult or too costly.

5. Don't use heavy duty extensions as a long term solution if possible.
   Similarly, don't use extensions with 'octopus' connections - install
   an outlet strip.

Extension cords of any type, capacity, and length can be easily constructed
from components and wire sold at most hardware stores and home centers.  This
is rarely economical for light duty polarized types as these are readily
available and very inexpensive.  However, for heavy duty 3 prong extensions,
a custom constructed one is likely to save money especially if an unusual
length is required.  Making up a heavy duty extension with a 'quad' electrical
box with a pair of 15 amp duplex outlets is a very rugged convenient
alternative to a simple 3 prong socket.

Common problems: internal wiring conductors broken at flex points (socket
or plug).  With yard tools, cutting the entire cord is common.  The connections
at the plug may corrode as well resulting in heating or a bad or intermittent

Testing: Extension cords can always be tested with a continuity checker or
multimeter on a the low ohms scale.

  6.5) Determining the location of a break in an extension cord

This isn't worth the time it would take to describe for a $.99 6 foot K-Mart
special but it might make sense for a 100 foot heavy duty outdoor type.  If
the problem is near one end, a couple of feet can be cut off and a new plug
or socket installed.  If more towards the middle, the wires can be cut and
spliced or two smaller cords could be made from the pieces.

But, how do you locate the break?

* Use a Time Domain Reflectometer (TDR).  Oops, don't have one?  And, you
  probably don't even know what this means!  (Basically, a TDR sends a pulse
  down a wire and measures how long it takes for a reflected pulse to return
  from any discontinuities.  The delay is a measure of distance.)  Don't
  worry, there are alternatives :-).

* If there is no obvious damage - you didn't attempt to mow the cord by
  accident - the most likely location is at the end where the plug of socket
  strain relief joins the wire.  Squeezing, squishing, pushing, etc., with the
  cord plugged into a live outlet and lamp or radio plugged into the other end
  may reveal the location by a momentary flash or blast of sound.  

* Try a binary search with a probe attached to a straight pin.  This works
  best with a cord where the wires are easily located - not the round double
  insulated type.  Attach one probe of your multimeter to the prong of the
  plug attached to the broken wire.  Start at the middle with your pin probe.
  If there is continuity move half the distance to the far end.  If it is
  open, move half the distance toward near end.  Then 1/4, 1/8, and so forth.
  It won't take long to located the break this way.  Of course, there will be
  pin holes in the insulation so this is not recommeded for outdoor extension
  cords unless the holes are sealed.

* You may be able to use one of those gadgets for testing Christmas Tree light
  sets - these inexpensive devices sense the AC field in proximity to its
  probe.  Plug the cord in so that the Hot of your AC line is connected to one
  of the wires you know is broken (from testing with an ohmmeter) and run the
  device along the cord until the light changes intensity.

  This also works for appliance cords where you are too lazy to go inside to
  check continuity.  You may need to try both wires in the cord to locate the
  broken one.

* If you have some real test equipment (but not a TDR!) attach the output of
  a frequency generator to the prong of the plug for the wire you know is
  broken.  Use an oscilloscope as a sensor - run the probe along the cord
  until the detected signal abruptly drops in intensity.

  An AM or multiband radio may also be suitable as a detector.

  (From: Asimov (Asimov@juxta.mn.pubnix.ten)).

  Try a capacitance ratio method. Simply measure the capacitance between the
  wires at both ends. The break should be at approximately the same distance
  ratio as that of the two measured capacitances.

  6.6) Internal wiring - cables and connectors

Wiring isn't super glamorous but represents the essential network of roads
that interconnect all of the appliance's internal parts and links it to the
outside world.

Inside the appliance, individual wires (often multicolored to help identify
function) or cables (groups of wires combined together in a single sheath
or bundle) route power and control signals to the various components.  Most
are insulated with plastic or rubber coverings but occasionally you will
find bare, tinned (solder coated), or plated copper wires.  In high temperature
appliances like space heaters and toasters, the insulation (if present) will
be asbestos (older) or fiberglass.  (Rigid uninsulated wires are also commonly
found in such applications.)  Particles flaking off from either of these
materials are a health hazard if you come in contact, inhale, or ingest them.
They are also quite fragile and susceptible to damage which may compromise
their insulating properties so take care to avoid excessive flexing or
repositioning of wires with this type of insulation.  Fiberglass insulation
is generally loose fitting and looks like woven fabric.  Asbestos is light
colored, soft, and powdery.

Color coding will often be used to make keeping track of the wires easier
and to indicate function.  However, there is no standard except for the
input AC line.  Generally, black will be used for Hot, white will be used
for Neutral, and green or uninsulated wire will be used for Safety Ground.
While this is part of the NEC (Code) for electrical wiring (in the U.S.), it
is not always followed inside appliances.  You may also find brown for Hot,
blue for Neutral, and green with a yellow stripe for Safety Ground.  This
is used internationally and is quite common for the cordsets of appliances
and electronic equipment.

Where a non-polarized plug (cordset) is used, either AC wire can be Hot and
both wires will typically (but not always) be the same color.

Other colors may be used for switched Hot (e.g., red), thermostat control,
motor start, solenoid 1, etc.  Various combinations of colored stripes may
be used as well.  Unfortunately, in some cases, you will find that all the
wiring is the same color and tracing the circuit becomes a pain in the

Where multiple wires need to go from point A to point B along the same path,
they will often be combined into a single cable which is bundled using nylon
or cloth tie-wraps or run inside a single large flexible plastic sheath.  For
electronic interconnects and low voltage control and signal wiring, molded
flat cables are common (like those for the cables to the diskette and hard
drives of your PC).  These are quite reliable and can be manufactured at low
cost by fully automatic machines.

The thickness of the insulation of a wire or cable is not a reliable indication
of its capacity or voltage rating.  A fat wire may actually have a very skinny
central conductor and vice-versa.  In some cases, the wire conductor size and
voltage rating will be printed on the insulation but this not that common.
If replacement is needed, this information will be essential.  However, the
ampacity (maximum current) can be determined from the size of the metal
conductor and for any of the line powered appliances discussed in this
document, wire with a 600 V rating should be more than adequate.

The type of insulation is critical in appliances that generate heat - including
table lamps and other lighting fixtures.  There is special high temperature
insulated wire (fixture wire) which should be used when replacement is needed.
For heating appliances like toasters, hair dryers, and deep friers, fiberglass
or high temperature silicone based rubber insulated wire or insulating sleeves
must be used should the original wiring need replacement.  An appliance repair
motor rebuilding shop would be the most likely source - common electronics
distributors may not carry this stuff (especially if you only need a couple

Connections between individual wires and between individual wires and other
components are most often made by crimp or screw terminals, welding, or
press-in contacts.  For cables, actual multipin and socket connectors may
be used.

Common problems: internal wiring conductors broken, corroded, or deteriorated
due to heat or moisture.  Dirty, corroded, weakened, or damaged connector
contacts are common requiring cleaning and reseating or replacement.  Damage
to insulation from vibration, heat, movement, or even improper manufacture or
design is also possible.  Careless reassembly during a previous repair could
result in pinched broken wires or insulation as well as short circuits between
wires, or wiring and sharp sheet metal parts.

Testing: Inspect for obvious breaks or wires that have pulled out of their
terminations.  Integrity of wiring can be determined with a continuity checker
or multimeter on a the low ohms scale.  Flexing and wiggling wires especially
at connections while observing the meter will identify intermittents.

  6.7) Switches - power, mode, or speed selection

Most appliances have at least one switch to turn the appliance on and off.
In some cases, this may be combined with a thermostat or other control.
However, switches serve a variety of functions as well.

* Power - Nearly all appliances that run on AC directly (no wall transformer)
  provide some means of completely disconnecting at least one side of the AC
  line when not in use.  This may be a rocker, slide, push-push, trigger,
  toggle, rotary, or other separate switch.  It may also be combined with
  another function like a speed control or thermostat.

* Selector, mode, function - these switches may be used to determine speed
  in a mixer or blender, or the heat or air-only setting on a blow-dryer,
  for example.

* Internal (not user accessible) - these perform functions like detecting
  the position of a mechanism (e.g., limit switch), cam operated timing,
  and other similar operations that are not directly performed by the user.

In all cases, the function of a switch is the same - to physically make (on)
or break (off) the circuit or connect one signal to another.

* The most common type of switches have a set of metallic contacts (special
  materials to resist arcing and corrosion) which are brought together as a
  result of mechanical motion of a rocker, lever, etc. to complete the circuit
  There is usually some sort of snap action to assure rapid make and break of
  the circuit to minimize deterioration due to arcing.

* Mercury switches - found in thermostats, silent wall switches, and a variety
  of other places, use a small quantity of mercury (a metal which is a liquid
  at room temperature) to complete the circuit.  Depending on the orientation
  of a glass or metal/insulator capsule, the mercury either contacts a set
  of terminals (on) or is separate from them (off).  Since any arcing occurs
  in the liquid mercury, there is virtually no deterioration of internal parts
  of a mercury switch.  Life is nearly infinite when used within its ratings.
  See the section: "About mercury wall switches".

Common problems with switches include: dirt, worn, or melted contacts, broken
plastic or fiber parts, bad connections to terminals.

Testing: Switches can always be tested with a continuity checker or a
multimeter on a low ohms scale.

WARNING: Mercury is a heavy metal and is poisonous.  I know it is fun to play
with beads and globs of the stuff (and I have done it) but do not recommend
it.  Dispose of any from broken mercury switches or thermometers safely.  If
you insist on keeping it, use a piece of paper as a scoop and put the mercury
in a bottle with a tightly sealed cap.

  6.8) About mercury wall switches

The types of mercury switches used for wall switches are quite clever and
provide in effect a snap action (called hysteresis) due to their construction
and the surface tension of the liquid mercury itself.  This despite the fact
that the motion of the toggle lever is totally smooth and silent.  It is not
possible to put the lever in such a position that there could be marginal
contact and random on-off cycles.  The mercury capsule inside such a switch
consists of a metallic shell with an insulating (glass or ceramic) spacer in
between the two halves.  Connection to the switch's wiring is made via sliding
contacts to the metal portion of the capsule.  There is a small hole toward
one side in the spacer.  Rotating the capsule results in the mercury flowing
through the hole to make contact:

* In the off position, the hole is above the level of the liquid mercury.

* In the on position, the hole is below the level of the liquid mercury.

* When turning the switch on, the hole is rotated below the surface and as
  soon as the mercury touches, surface tension quickly pulls it together.
  There is no 'contact bounce'.

* When turning the switch off, the mercury pulls apart as the capsule is
  rotated to raise the hole.  Eventually, surface tension is not sufficient to
  hold the two globs of mercury together and they part suddenly.

Problems are rare with these mercury switches.  In fact, GE mercury switches
used to carry a *50* year warranty!  I don't know if they still do.

In principle, these are also the safest type of switch since any sparking or
arcing takes place inside the sealed mercury capsule.  However, the contact
between the screw terminals and the capsule are via sliding contacts (the
capsule is press fit between the metal strips to which the screws are attached)
and with time, these can become dirty, worn, or loose.  For this reason, some
electricians do not like mercury switches, particularly for high current

  6.9) Relays - electrically activated switches for power or control

Relays are switches that are activated by an electrical signal rather
than a button or toggle.  They are used to switch power (as in an central
air conditioning system) or control signals (as in a telephone or modem).

* The most common relays are electromechanical - an electromagnet is used
  to move a set of contacts like those in a regular switch.

* Solid state relays have no moving parts.  They use components like thyristors
  or transistors to do the switching.

For more information on relays, see the document: "Notes on the Troubleshooting and Repair of Audio Equipment and other Miscellaneous Stuff".

  6.10) Contact configurations

The arrangement of contacts on a switch is often abbreviated mPnT where:

* 'm' identifies the number of separate sets of contacts.

* 'P' stands for Poles or separate sets of contacts.

* 'n' identifies the number of contact positions.

* 'T' stands for Throw which means the number of contact positions.

In addition, you may see:

* NC (Normally Closed and NO (Normally Open) may be used to designate terminals
  when the switch is in the off or deactivated state.  This applies to power
  switches where OFF would be down or released and ON would be up or pushed in.
  It also applies to momentary pushbutton switches and relays.

* MBB (Make Before Break) and BBM (Break Before Make) designate how the
  connections behave as the switch is thrown.  Most switches found in small
  appliances will be of the BBM variety.

This also applies to relays except that the contact switching is activated
by an electrical signal rather than a finger.

The most common types are:

* SPST - Single Pole Single Throw.  Terminal (A) is connected to terminal (B)
  when the switch is on:

        A ______/ _______ B

  This is the normal light or power switch.  For electrical (house) wiring,
  it may be called a '2-way' switch.

* DPST - Double Pole Single Throw.  Terminal (A) is connected to terminal (B)
  and terminal (C) is connected to terminal (D) when the switch is on:

        A ______/ _______ B
        C ______/ _______ D

  This is often used as a power switch where both wires of the AC line are
  switched instead of just the Hot wire.

* SPDT - Single Pole Double Throw.  A common terminal (C) is connected to
  either of two other terminals:

                 _______ NC
       C ______/
                 _______ NO

  This is the same configuration as what is known as a '3-way' switch for
  electrical (house) wiring.  Two of these are used to control a fixture
  from separate locations.
* DPDT - Double Pole Double Throw.  Essentially 2 SPDT switches operated by
  a single button, rocker, toggle, or lever:

                 _______ NC1
      C1 ______/
               : _______ NO1
               : _______ NC2
      C2 ______/
                 _______ NO2

* SP3T, SP4T, etc. - Single Pole selector switch.  A common terminal (C) is
  connected to one of n contacts depending on position.  An SP5T switch is
  shown below:
               _________ 1
                 _______ 2
       C ______/  ______ 3
                 _______ 4
               _________ 5

  6.11) Electrical overload protection devices - fuses and circuit breakers

The purpose of fuses and circuit breakers is to protect both the wiring
from heating and possible fire due to a short circuit or severe overload
and to prevent damage to the equipment due to excess current resulting
from a failed component or improper use (using a normal carpet vacuum
to clear a flooded basement).

Fuses use a fine wire or strip (called the element) made from a metal which
has enough resistance (more than for copper usually) to be heated by current
flow and which melts at a relatively low well defined temperature.  When the
rated current is exceeded, this element heats up enough to melt (or vaporize).
How quickly this happens depends on the extent of the overload and the type
of fuse.

Fuses found in consumer electronic equipment are usually cartridge type -
1-1/4" mm x 1/4" or 20 mm x 5 mm, pico(tm) fuses that look like green 1/4 W
resistors, or other miniature varieties.  Typical circuit board markings are
F or PR.

Circuit breakers may be thermal, magnetic, or a combination of the two.
Small (push button) circuit breakers for appliances are nearly always
thermal - metal heats up due to current flow and breaks the circuit
when its temperature exceeds a set value.  The mechanism is often the
bending action of a bimetal strip or disc - similar to the operation of
a thermostat.  Flip type circuit breakers are normally magnetic.  An
electromagnet pulls on a lever held from tripping by a calibrated spring.
These are not usually common in consumer equipment (but are used at the
electrical service panel).

At just over the rated current, it may take minutes to break the circuit.
At 10 times rated current, the fuse may blow or circuit breaker may open
in milliseconds.

The response time of a 'normal' or 'rapid action' fuse or circuit breaker
depends on the instantaneous value of the overcurrent.

A 'slow blow' or 'delayed action' fuse or circuit breaker allows instantaneous
overload (such as normal motor starting) but will interrupt the circuit
quickly for significant extended overloads or short circuits.  A large thermal
mass delays the temperature rise so that momentary overloads are ignored.  The
magnetic type breaker adds a viscous damping fluid to slow down the movement
of the tripping mechanism.

Common problems: fuses and circuit breakers occasionally fail for no reason
or simply blow or trip due to a temporary condition such as a power surge.
However, most of the time, there is usually some other fault with the
appliance which will require attention like a bad motor or shorted wire.

Testing: Fuses and circuit breakers can be tested for failure with a
continuity checker or multimeter on the low ohms scale.  A fuse that tests
open is blown and must be replaced (generally, once the circuit problem is
found and repaired.)  Of course, if the fuse element is visible, a blown
fuse is usually easy to identify without any test equipment.  A circuit
breaker that tests open or erratic after the reset button is pressed, will
need replacement as well.

  6.12) Fuse postmortem

Quite a bit can be inferred from the appearance of a blown fuse if the
inside is visible as is the case with a glass cartridge type.  One
advantage to the use of fuses is that this diagnostic information is
often available!

* A fuse which has an element that looks intact but tests open may have just
  become tired with age.  Even if the fuse does not blow, continuous cycling
  at currents approaching its rating or instantaneous overloads results in
  repeated heating and cooling of the fuse element.  It is quite common for
  the fuse to eventually fail when no actual fault is present.

* A fuse where the element is broken in a single or multiple locations blew
  due to an overload.  The current was probably more than twice the fuse's
  rating but not a dead short.

* A fuse with a blackened or silvered discoloration on the glass where the
  entire element is likely vaporized blew due to a short circuit.

This information can be of use in directly further troubleshooting.

  6.13) Fuse or circuit breaker replacement

As noted, sometimes a fuse will blow for no good reason.  Replace fuse,
end of story.  In this situation, or after the problem is found, what are
the rules of safe fuse replacement?  It is inconvenient, to say the least,
to have to wait a week until the proper fuse arrives or to tromp out to
Radio Shack in the middle of the night.

Even with circuit breakers, a short circuit may so damage the contacts or
totally melt the device that replacement will be needed.

Five major parameters characterizes a fuse or circuit breaker:

1. Current rating - this should not be exceeded (you have heard about not
   putting pennies in fuse boxes, right?)  (The one exception to this rule
   is if all other testing fails to reveal which component caused the fuse to
   blow in the first place.  Then, and only then, putting a larger fuse in
   or jumpering across the fuse  **just for testing** will allow the faulty
   component to identify itself by smoking or blowing its top!)  A smaller
   current rating can safely be used but depending on how close the original
   rating was to the actual current, this may blow immediately.

2. Voltage rating - this is the maximum safe working voltage of the circuit
   (including any inductive spikes) which the device will safety interrupt.
   Thus, you may see fuses where the elements look like [|------|] versus
   [|==--==|].  It is safe to use a replacement with an equal or high voltage

3. AC versus DC - fuses rated for AC and DC may not be the same.  For a given
   voltage, a shorter gap can be used to reliably interrupt an AC circuit
   since the voltage passes through zero 120 (100) times a second.  For
   example, a fuse rated 32 VDC may look similar to one rated for 125 VAC.

4. Type - normal, fast blow, slow blow, etc.  It is safe to substitute
   a fuse or circuit breaker with a faster response characteristic but
   there may be consistent or occasional failure mostly during power-on.
   The opposite should be avoided as it risks damage to the equipment
   as semiconductors tend to die quite quickly.

5. Mounting - it is usually quite easy to obtain an identical replacement.
   However, as long as the other specifications are met, soldering a normal
   1-1/4" (3AG) fuse across a 20 mm fuse is perfectly fine, for example.
   Sometimes, fuses are soldered directly into an appliance.

  6.14) Thermal protection devices - thermal fuses and thermal switches

These devices protect against excessive temperature due to either a fault
in the appliance (locked motor overheating), improper use (blow dryer air

There are three typical types:

1. Thermal fuses.  This is similar to an electrical fuse but is designed
   to break the circuit at a specific temperature.  These are often found
   in heating appliances like slow cookers or coffee percolators or buried
   under the outer covering of motor windings or transformers.  Some also
   have an electrical fuse rating as well.  Like electrical fuses, these
   are one-time only parts.  A replacement that meets both the thermal and
   electrical rating (if any) is required.

   CAUTION: When replacing a thermal fuse, DO NOT SOLDER it if at all
   possible.  If the device gets too hot, it may fail immediately or be
   weakened.  Crimp or screw connections are preferred.  If you must solder,
   use a good heat sink (e.g., wet paper towels, little C-clamps) on the leads
   between the thermal fuse and the soldering iron, and work quickly!

2. Thermal switches or thermal protectors (strip type).  These use a strip of
   bimetal similar to that used in a thermostat.  Changes in temperature
   cause the strip to bend and control a set of contacts - usually to
   to break a circuit if the set temperature is exceeded.  Commonly found
   in blow dryers and other heating appliances with a fixed selection of
   heat settings.  They may also be found as backup protection in addition
   to adjustable thermostats.

3. Thermal switches or thermal protectors (disk).  These use a disk of bimetal
   rather than a strip as in most thermostats.  The disk is formed slightly
   concave and pops to the opposite shape when a set temperature is exceeded.
   This activates a set of contacts to break (usually) a circuit if the rated
   temperature is exceeded.  They may also be found as backup protection in
   addition to adjustable thermostats.  A typical thermal switch is a small
   cylindrical device (i.e., 3/4" diameter) with a pair of terminals and a
   flange that is screwed to the surface whose temperature is to be monitored.

In some applications, device types (2) and (3) may be used as the primary
temperature regulating controls where adjustment is not needed.

  6.15) More on thermal fuses

(From: Paul Grohe (grohe@galaxy.nsc.com)).

The following is From Microtemps' literature (`95 EEM Vol.B p1388):

"The active trigger mechanism of the thermal cutoff (TCO) is an electrically
 non-conductive pellet. Under normal operating temperatures, the solid pellet
 holds spring loaded contacts closed. When a pre-determined temperature is
 reached, the pellet melts, allowing the barrel spring to relax. The trip
 spring then slides the contact away from the lead and the circuit is opened.
 Once TCO opens a circuit, the circuit will remain open until the TCO is

Be very careful in soldering these. If the leads are allowed to get too hot, it
may "weaken" the TCO, causing it to fail prematurely. Use a pair of needle-nose
pliers as heat sinks as you solder it.

I have replaced a few of these in halogen desk lamp transformers.  The
transformers showed no signs of overheat or overload. But once I got it
apart, the TCO's leads had large solder blobs on them, which indicated
that the ladies that assembled the transformers must have overheated the
cutouts leads when they soldered them.

The NTE replacement package also comes with little crimp-rings, for high-temp
environments where solder could melt or weaken (or to avoid the possibility
of soldering causing damage as described above --- sam).

  6.16) Controls 1 - adjustable thermostats and humidistats

Thermostats are use to regulate the temperature in heating or cooling type 
appliances.  Common uses include heaters, airconditioners, refrigerators,
freezers, hair dryers and blow dryers, toaster ovens and broilers, waffle
irons, etc.  These are distinguished from the thermal switches discussed
above in that they usually allow a variable temperature setting.

Four types are typically found in appliances.  The first three of these
are totally mechanically controlled:

1. Bimetal strip.  When two metals with different coefficients of thermal
   expansion are sandwiched together (possibly by explosive welding), the
   strip will tend to bend as the temperature changes.  For example, if the
   temperature rises, it will curve towards the side with the metal of lower
   coefficient of expansion.

   In a thermostat, the bimetal strip operates a set of contacts which make
   or break a circuit depending on temperature.  In some cases the strip's
   shape or an additional mechanism adds 'hysteresis' to the thermostat's
   characteristics (see the section: "What is hysteresis?").

2. Bimetal disk.  This is similar to (1) but the bimetal element is in the
   shape of a concave disk.  These are not common in adjustable thermostats
   but are the usual element in an overtemperature switch (see the section:
   "Thermal protection devices - thermal fuses and thermal switches").

3. Fluid operated bellows.  These are not that common in small appliances
   but often found in refrigerators, airconditioners, baseboard heaters,
   and so forth.  An expanding fluid (alcohol is common) operates a bellows
   which is coupled to a set of movable contacts.  As with (1) and (2) above,
   hysteresis may be provided by a spring mechanism.

Other variations on these basic themes are possible but (1)-(3) cover the
vast majority of common designs.

Testing of mechanical thermostats: examine for visible damage to the
contacts.  Use a continuity checker or ohmmeter to confirm reliable
operation as the knob or slider is moved from end to end if it will
switch at room temperature.  Gently press on the mechanism to get the
contacts to switch if this is not possible.  Use an oven on low or a
refrigerator or freezer if needed to confirm proper switching based
on temperature.

4. Electronic thermostats.  These typically use a temperature variable
   resistance (thermistor) driving some kind of amplifier or logic circuit
   which then controls a conventional or solid state relay or thyristor.
Testing of electronic thermostats:  This would require a schematic to
understand exactly what they are intended to do.  If a relay is used, then
the output contacts could perhaps be identified and tested.  However,
substitution is probably the best approach is one of these is suspected
of being defective.

Humidistats, as their name implies, are used to sense relative humidity
in humidifiers and dehumidifiers.  Their sensing material is something
that looks kind of like cellophane or the stuff that is used for sausage
casings.  It contracts and expands based on the moisture content of the
air around it.  These are somewhat fragile so if rotating the control
knob on a humidifier or dehumidifier does not result in the normal 'click',
this material may have been damaged or broken.

Testing of mechanical humidistats: examine for visible damage to the
contacts.  Use a continuity checker or ohmmeter to confirm reliable
operation as the knob or slider is moved from end to end.  Gently press
on the mechanism to get the contacts to switch if this is not possible.
Gently exhale across the sensing strip to confirm that the switching point

  6.17) What is hysteresis?

An intuitive explanation of hysteresis is that it is a property of a
system where the system wants to remain in the state that it is in -
it has memory.

Examples of systems with hysteresis:

* Thermostats - without hysteresis your heater would be constantly
  switching on and off as the temperature changed.  A working thermostat
  has a few degrees of hysteresis.  As the temperature gradually increases,
  at some point the thermostat switches off.  However, the temperature then
  needs to drop a few degrees for it to switch on again.

* Toggle switches - the click of a toggle switch provides hysteresis to
  assure that small vibrations, for example, will not accidentally flip
  the switch.

Examples of systems which ideally have little or no hysteresis:

* Audio amplifiers - input vs. output.

* Pendulums on frictionless bearings - force vs. position.

Hysteresis is usually added thermostats by the use of a spring mechanism
which causes the mechanism to want to be in either the open or closed
position but not in between.  Depending on the appliance, there may be
anywhere from 0 hysteresis (waffle iron) to 5-10 degrees F (space heater).
Sometimes, the thermal mass of the heated device or room provides the
hysteresis since any change to the temperature will not take place
instantaneously since the heating element is separated from the thermostat
by a mass of metal.  Therefore, some overshoot - which in effect performs the
same function as a hysteresis mechanism - will take place.

  6.18) Controls 2 - rheostats and potentiometers

These controls are usually operated by a knob or a slide adjustment and
consist of a stationary resistance element and a wiper that can be moved
to determine where on the fixed element it contacts.  In some cases, they
are not actually user controls but are for internal adjustments.  In other
cases, they are operated by the mechanism automatically and provide a means
of sensing position or controlling some aspect of the operation.

* Rheostats provide a resistance that can be varied.  Usually, the range is
  from 0 ohms to some maximum value like 250 ohms.  They are used to
  control things like speed and brightness just by varying the current
  directly, or via an electronic controller (see the section: "Electronic controllers - simple delay or microprocessor based").

                 B o-------------+
                 A o--------/\/\/\/\/\-----
                         250 ohm rheostat

  In the diagram above, the resistance changes smoothly from 0 to 250 ohms
  as the wiper moves from left to right.

  Very often, you will see the following wiring arrangement:

                 B o-------------+------+
                                 |      |
                                 V      |
                 A o--------/\/\/\/\/\--+
                        250 ohm rheostat

  Electrically, this is identical.  However, should the most common failure
  occur with the wiper breaking or becoming disconnected, the result will be
  maximum resistance rather than an open circuit.  Depending on the circuit,
  this may be preferred - or essential for safety reasons.

  Testing: Disconnect at least one of the terminals from the rest of the
  circuit and then measure with an ohmmeter on the appropriate scale. The
  resistance should change smoothly and consistently with no dead spots or

* Potentiometers are either operated by a knob or a slide adjustment and
  implement a variable resistance between two end terminals as shown below.
  This can be used to form a variable voltage divider.  A potentiometer (or
  'pot' for short) can be used like a rheostat by simply not connecting one
  end terminal.  These are most often used with electronic controllers.

                 B o-------------+
                 A o--------/\/\/\/\/\--------o C
                       1K ohm potentiometer

  In the diagram above, the resistance between A and B varies smoothly from
  0 to 1K ohms as the wiper moves from left to right.  At the same time, the
  resistance between B and C varies smoothly from 1K to 0 ohms.  For some
  applications, the change is non-linear - audio devices in particular so that
  the perceived effect is more uniform across the entire range.

  Testing: Disconnect at least two of the terminals from the rest of the
  circuit and then measure with an ohmmeter on the appropriate scale.
  The resistance should change smoothly and consistently with no dead
  spots or dips.  Try between each end and the wiper.  Check the resistance
  across the end terminals as well - it should be close to the stamped
  rating (if known).

Rheostats and potentiometers come in all sizes from miniature circuit board
mounted 'trimpots' to huge devices capable of handling high power loads.
The resistance element may be made of fine wire ('wirewound') or a carbon
composition material which is silkscreened or painted on.

  6.19) Interlocks - prevent operation with case or door open

Most of these are simple switches mechanically activated by the case or door.
Sometimes, optical or magnetic interlocks are used (rare on small appliances
but common on things like printers).  Line cords that are firmly attached to
the case and disconnect automatically when the case is removed are another
example of an interlock.  Interlocks may be designed to prevent injury during
normal operation (e.g.. food processor blades will not start when cover is
removed) or during servicing (remove AC power to internal circuits with case

1. Interlock switches.  Various kinds of small switches may be positioned
   in such a way that they disconnect power when a door is opened or cover
   is removed.  These may fail due to electrical problems like worn or
   dirty contacts or mechanical problems like a broken part used to activate
   the interlock.

   Testing: Use an ohmmeter or continuity checker on the switches.  The reading
   should either be 0 ohms or infinite ohms.  Anything in between or erratic
   behavior is indication of a bad switch or cord.

2. Attached cordset.  Should the case be opened, the cord goes with the case
   and therefore no power is present inside the appliance.  To get around
   this for servicing, a 'cheater cord' is needed or in many cases the
   original can be easily unfastened and used directly.

   Testing: Use an ohmmeter or continuity check to confirm that both wires
   of the cord are connected to both AC plug and appliance connector.  Wiggle
   the cord where it connects to the appliance and at the plug end as well to
   see if there might be broken wires inside.

  6.20) Light bulbs - incandescent and fluorescent

Small incandescent light bulbs are often used in appliances for interior
lighting or spot illumination.  The common 'appliance bulb' is simply
a 'ruggedized' 40 W incandescent light bulb in a clear glass envelope.
Other types are found in vacuum cleaners, microwave overs, makeup mirrors,
and so forth.

Testing: visual inspection will often reveal a burnt out incandescent light
bulb simply because the filament will be broken.  If this is not obvious,
use an ohmmeter - an infinite resistance means that the bulb is bad.

Small fluorescent lamps are often found in makeup mirrors, plant lights, and
battery powered lanterns.

Testing: The best test for a bad fluorescent bulb is to substitute a known
good one.  Unfortunately, there is no easy go-no go test for a fluorescent
lamp.  Other parts of the lamp or fixture (like the ballast or starter) could
also be bad.

See the sections on the appropriate lamp type for additional information.

  6.21) Indicators - incandescent or neon light bulbs or LEDs

Whereas lighting fixtures using incandescent or fluorescent bulbs are designed
to illuminate a room or small area, an indicator is simply there to let you
know that an appliance is on or in a specific mode.

There are three common types of electrical indicator lights:

1. Incandescent bulbs.  Just like their larger cousins, an incandescent
   indicator or pilot light has a filament that glows yellow or white hot
   when activated by a usually modest (1.5-28 V) source.  Flashlight
   bulbs are very similar but usually have some mechanical method of
   keeping the filament positioned reasonably accurately so that the
   light can be focussed by a reflector or lens.  Since the light spectrum
   of incandescent indicators is quite broad, filters can be used to obtain
   virtually any colored light.  Incandescent indicator lamps do burn out
   just like 100 W bulbs if run near their rated voltage.  However, driving
   these bulbs at reduced voltage can prolong their life almost indefinitely.

   Incandescent indicator lamps are often removable using a miniature screw,
   bayonet, or sliding type base.  Some are soldered in via wire leads.  Others
   look like cartridge fuses.

   Testing: Visual inspection will often reveal a burnt out incandescent light
   bulb simply because the filament will be broken.  If this is not obvious,
   use an ohmmeter - an infinite resistance is means that the bulb is bad.

2. Neon lamps.  These are very common as AC line power indicators because
   they are easy to operate directly from a high voltage requiring only a
   high value series resistor.

   They are nearly all the characteristic orange neon color although other
   colors are possible and there is a nice bright green variety with an
   internal phosphor coating that can actually provide some illumination
   as well.  While neon bulbs do not often burn out in the same sense as
   incandescent lamps, they do darken with age and may eventually cease to
   light reliably so flickering of old Neon bulbs is quite common.

   Some Neon bulbs come in a miniature bayonet base.  Most are soldered
   directly into the circuit via wire leads.

   Testing: Inspect for a blackened glass envelope.  Connect to AC line
   (careful - dangerous voltage) through a series 100K resistor.  If glow
   is weak or absent, Neon bulb is bad.

3. Light Emitting Diodes (LEDs).  LEDs come in a variety of colors - red,
   yellow, and green are very common; blue is just appearing.  These run
   on low voltage (1.7-3 V) and relatively low currents (1-20 mA).  Thus,
   they run cool and are easily controlled by low voltage logic circuits.
   LEDs have displaced incandescent lamps in virtually all electronic
   equipment indicators and many appliances.  Their lifetime easily exceeds
   that of any appliance so replacement is rarely needed.

   LEDs are almost always soldered directly into the circuit board since they
   rarely need replacement.

   Testing: Use a multimeter on the diode test scale.  An LED will have a
   forward voltage drop of between 1.7 and 3 V.  If 0 or open, the LED is
   bad.  However, note: some DMMs may not produce enough voltage on the diode
   test scale so the following is recommended:  Alternative: Use a 6 to 9 V DC
   supply in series with a 470 ohm resistor. LED should light if the supply's
   positive output is on the LED's anode.  If in doubt, try both ways,  If the
   LED does not light in either direction, it is bad.

  6.22) Heating elements - NiChrome coils or ribbon, Calrod, Quartz

All heating elements perform the same function: convert electricity into
heat.  In this they have one other characteristic in common: they are all
nearly 100% efficient.  The only electrical energy which does not result in
heat is the slight amount of light (usually red-orange) that is produced
by a hot element.

There are 3 basic types of heating elements.  Nearly every appliance on
the face of the planet will use one of these:

1. NiChrome coil or ribbon.  NiChrome is an alloy of Nickel and Chromium
   which has several nice properties for use in heating appliances - First,
   it has a modest resistance and is thus perfect for use in resistance
   heating elements.  It is easily worked, is ductile, and is easily formed
   into coils of any shape and size.  NiChrome has a relatively high melting
   point and will pretty much retain its original shape and most importantly,
   it does not oxidize or deteriorate in air at temperatures up through the
   orange-yellow heat range.

   NiChrome coils are used in many appliances including toasters, convection
   heaters, blow-dryers, waffle irons and clothes dryers.

   The main disadvantage for our purposes is that it is usually not possible
   to solder this material due to the heating nature of its application.
   Therefore, mechanical - crimp or screw must be used to join NiChrome
   wire or ribbon to another wire or terminal.  The technique used in the
   original construction is may be spot welding which is quick and reliable
   but generally beyond our capabilities.

   Testing: Visual inspection should reveal any broken coil or ribbon.  If
   inspection is difficult, use a multimeter on the low ohms scale.  Check
   for both shorts to the metal chassis as well as an open element (infinite

2. Calrod(tm) enclosed element.  This encloses a fine coiled NiChrome wires
   in a ceramic filler-binder inside a tough metal overcoat in the form of a
   shaped rod with thick wire leads or screw or plug-in terminals.

   These are found in toaster oven/broilers, hot plates, coffee makers,
   crock pots and slow cookers, electric range surface elements, conventional
   and convection ovens and broilers.

   Testing: When these fail, it is often spectacular as there is a good
   chance that the internal NiChrome element will short to the outer casing,
   short out, and melt.  If there is no visible damage but the element does
   not work, a quick check with an ohmmeter should reveal an open element or
   one that is shorted to the outer casing.

3. Quarts incandescent tube.  These are essentially tubular high power
   incandescent lamps, usually made with a quartz envelope and thus their

   These are found in various kinds of radiant heaters.  By running a less
   than maximum power - more orange heat - the peak radiation is in the
   infra-red rather than visible range.

   Testing: Look for a broken filament.  Test with an ohmmeter just like
   an incandescent light bulb.

  6.23) Repair of broken heating elements

In appliances like waffle irons and toaster ovens, these are usually welded.
This is necessary to withstand the high temperatures and it is cheap and
reliable as well.  Welding is not normally an option for the doit yourselfer.  
However, if you are somewhat suicidal, see the section: "Improvised welding repair of heating elements" for a more drastic approach.

I have used nuts and bolts, say 6-32, bolt, wire, washer, wire, washer,
lockwasher, nut.  Depending on how close to the actual really hot element
it is, this may work.  If you are connecting to the coiled element, leave
a straight section near the joint - it won't get as hot.

The use of high temperature solder or brazing might also work.

The best approach is probably to use high temperature crimp connectors:

(The following from: sad@garcia.efn.org (Stephen Dunbar))

You can connect heating element wires with high-temperature solderless
connectors that are crimped onto the wires. Be sure to get the special
high-temp connectors; the ordinary kind will rapidly oxidize and fall apart at
high temperatures. If you want to join two wires to each other, you'll need
either a butt splice connector (joins the wires end-to-end) or a parallel
splice connector (the wires go into the connector side-by-side). To fasten
a wire to a screw terminal you can use a ring or spade connector (though
as noted above, a screw, nut, and washer(s) should work fine --- sam). If your
waffle iron has quick disconnect terminals you'll need the opposite gender
disconnect (AKA Faston). These come in both .187" and .250" widths. 

Your best bet for getting these connectors in small quantity is probably a
local appliance parts outlet that caters to do-it-yourselfers. If you can't
find what you need there, try Newark Electronics (branches all over the
place). I have an old copy of their catalog which lists SPC Technology
Voltrex Brand High Temperature Barrel Terminals in several styles: ring,
spade, disconnect, and butt splice. The prices were around $10 to $12 per
100 (this catalog is a couple of years old) for wires in the 22-18 or
16-14AWG size ranges, almost twice that for the heftier wire gauges. (Be
sure to determine the wire gauge of your heating elements so you can get the
right size terminal.) 

You can spend a *lot* of money on crimp tools, but for occasional light use
you can probably get by with one of those $10 gadgets that crimp, strip &
cut wires, and cut bolts--the sort of thing you'd find in your local home
center or Radio Shack.

(From: Nigel Cook (diverse@tcp.co.uk)).

The thin stainless steel strip found spot welded to multicell NiCd batteries
make good crimps for joining breaks in heater resistance wire.  Form a small
length of this strip around a needle or something similar to make a tight
spiral with enough clearance to go over doubled-up heater wire.  Abraid or
file the cut ends of the broken wire.  Crimp into place with a double lever
action crimper.  If there is an area of brittle heating element around the
break then cut out and splice in a replacement section with two such crimps.
Such a repair to my hot-air paint stripper (indispensable tool in my
electronics tool-kit) has survived at least 50 hours.

(From: Dan Sternberg (steberg@erols.com)).

Another old trick for nichrome repair is to make a paste of Borax, twist the
two broken end together, and energize the circuit.  A form of bond welding
takes place.  I've have used this on electric clothes dryer heater elements
with good luck.

  6.24) Solenoids - small and large

Solenoids are actuators operated by electromagnets that are used to operate
valves, slide or engage various parts, eject or prevent opening of a door,
and other functions.  While shapes and sizes may vary, all electrically
operated solenoids use an electromagnet - AC or DC - to pull on a movable
piece called an armature which generally moves back and forth but rotary
motion is also possible.

Solenoids are usually two position devices - they are not used to provide
intermediate amounts of force or travel like motors.

Sizes ranges from small 1/2" long units providing a fraction of an ounce of
force and 1/8" travel to large 3" long units providing many pounds of force
with travels of 2" or more.

Testing: Inspect for free movement.  Use an ohmmeter to confirm that the
coil is intact.  There could be other problems like shorted turns in the
coil but these would be less common than lack of lubrication or an open
coil.  Check voltage on operating solenoid to determine whether drive power
is present.

  6.25) Small electronic components - resistors, capacitors, diodes

A variety of small electronic components may be found in appliances though
unlike true electronic equipment, these do not usually run the show.

Resistors - may be used in various ways to adjust the current flowing in
part of a circuit.  Many different types of resistors are possible - tiny
carbon or metal film types looking like small cylindrical objects often
with colored bands which indicate the value.

Power resistors - larger cylindrical or rectangular often ceramic coated.
These may get quite hot during operation.  Their resistance value and power
rating are usually printed on the resistor.

Capacitors - a variety of shapes and sizes.  Some may look like disks,
jelly beans, cylinders, boxes, etc.  Their value is often marked in uF or pF.

Diodes or rectifiers - solid state devices that permit electric current
to only flow in one direction (positive current in the direction of the
arrow when marked this way).  These are most often used in appliances to
change AC to DC or to cut the power to a motor or heater (by allowing only
half of the AC current to pass).

For more information on these types of components, see any good introductory
electronics text.

  6.26) Motors - universal, induction, DC, timing

A large part of the functionality of modern appliances is based on the
use of motors of one form or another.  We devote an entire chapter to
motors.  The following is just an introduction.

Motors come in all shapes and sizes but most found in small appliances
can be classified into 5 groups:

        1. Universal motors.
        2. Single phase induction motors
        3. Shaded pole induction motors.
        4. Small permanent magnet DC motors.
        5. DC brushless motors.
        6. Synchronous timing motors.

See the chapter: "Motors 101" for more detailed information on the common
types of motors found in small appliances.

  6.27) Fans and Blowers - bladed or centrifugal

The entire purpose of a particular appliance may be to move air or this
may simply be needed for cooling.  Obviously, portable and window fans
are an example of the former.  However, many appliances have built in fans
you may not even be aware of as part of the motor(s) or other rotating

There are two primary types of configurations:

1. Bladed fans - we are all familiar with the common desk or window fan.
   This uses a set of rotating blades - typically 3-5 to gather and direct
   air.  In the specific case of an oscillating desk fan, a gear drive
   linked to the motor also permits the general direction of air movement
   to be controlled in a back-and-forth motion.  I recently saw one where
   in addition to moving back and forth, the front grille can be set to
   rotate at an adjustable rate providing more variation in air flow.

   The direction of the air movement with respect to blade rotation is
   determined by the pitch - the tilt - of the blades.  Although reversing
   air direction is possible by reversing the motor, one direction is usually
   more effective than the other due to the curve of the blades.

2. Centrifugal blowers.  These use a structure that looks similar to a
   squirrel cage to suck air from the center and direct it out a plenum
   formed around the blower.  While these may be found in all sizes, the
   most common household application is in the vacuum cleaner.  Large
   versions of these blowers are used in central heating and airconditioning
   systems, window airconditioners, and oil burners.

   Direction of rotation of the blower motor does not change the direction
   of airflow.  However, one direction will be more effective than the
   other (where the blower is rotating in the same direction as the way exit
   port on the air plenum points.  Because of this, it is not possible for a
   vacuum cleaner to blow out the suction hose due to a reversed motor (which
   in itself is for all intents and purposes, impossible as well).  This is
   usually caused by back flow due to a blockage.

  6.28) Bearings and bushings

The shafts of rotating parts normally are mounted in such a way that friction
is minimized - to the extent needed for the application.  A bearing is any such
joint with more specific terms used to describe the typical types found in
small appliances - or lawnmower, automobile engines, or 100 MW turbines.

Plain bearings - these consist of an outer sleeve called a bushing in which
a polished shaft rotates.  The bushing may be made of a metal like brass or
bronze or a plastic material like Teflon(tm).  The shaft is usually made of
steel though other materials may be found depending on the particular needs.
Where a metal bushing is used, there must be means provided for lubrication.
This may take the form of oiling grooves or holes and an oil reservoir (usually
a saturated wad of felt) or the bushing itself may be sintered.   Metal
particles are compressed at high temperature and pressure resulting in a
very porous but strong material which retains the lubricating oil.

Under normal conditions, a plain bearing wears only during start and stop
cycles.  While the shaft is rotating at any reasonable speed, there is no
metal to metal contact and thus no wear.  With a properly designed and
maintained bearing of this type, a very thin oil film entirely supports
the shaft - thus the importance of clean oil.  Your automobile engine's
crankshaft is entirely supported by these types of bearings.

Eventually, even 'lubricated for life' bearings of this type may need to be
disassembled, cleaned, and lubricated.  The plain bearings in small appliances
must be lubricated using a proper light oil like electric motor or machine
oil - not automotive engine oil and NEVER NEVER WD40.

NEVER, ever, use WD40 as a lubricant (unless specifically recommended by the
manufacturer of the equipment, that is)!  WD40 is not a good lubricant despite
the claims on the label.  Legend has it that the WD actually is an abbreviation
for Water Displacer - which is one of the functions of WD40 when used to coat
tools.  WD40 is much too thin to do any good as a general lubricant and will
quickly collect dirt and dry up.  It is also quite flammable and a pretty good
solvent - there is no telling what will be affected by this.

WD40 has its uses but lubrication unless specifically recommended by the
manufacturer (of the equipment, that is) is not one of them.  Results initially
may be good with that instant gratification that comes from something returning
to life.  However, the lighter fractions of WD40 evaporate in a few days 

For very small metal-in-plastic types, the following might be useful:

(From: Frank MacLachlan (fpm@bach.n2.net)).

"I've had good luck with a spray lubricant called SuperLube.  It contains a
 solvent which evaporates and leaves a Teflon film which doesn't migrate
 or retain dust.  I spray some into a spray paint cap and then apply the
 solution with a toothpick, allowing the lubricant to wick into the bearing
 areas.  Worked great for some balky Logitech mice I purchased at a local
 swap meet."

Frictionless bearings are usually of the ball or roller variety.  An inner
ring called a race rotates supported by a series of balls or rollers inside
an outer race.  There is virtually no friction even at stand-still with these
bearings.  However, rolling metal to metal contact is maintained at all speeds
so they are not quite as wear free as a properly maintained and constantly
rotating plain bearing.  However, for all practical purposes in small
appliances, these will last a long time and are rarely a problem.

Sometimes, reworking an appliance to use a ball bearing instead of a plain
bearing is a worthwhile effort - I have done this with electric drills and
shop vacs.  They run smoother and quieter with ball bearings.  Not
surprisingly, higher-end models of these devices (which use ball bearings)
share parts with the cheaper versions and finding standard ball bearings
that would fit was not difficult.

  6.29) Mechanical controllers - timing motors and cam switches

While these are not that common on small appliances, they may be present
in washing machines, dryers, dishwashers. and refrigerator defrost timers.
They in themselves may be considered small appliances - and often can be
repaired or replaced easily.

Most of these are just small timing motors (synchronous motors running
off of the AC line) which rotate one or more cams (disks with bumps) which
activated one or more switches at appropriate times during the rotation
cycle.  Typical cycle times range from a minute or less to several hours
(refrigerator defrost timer).  Most like washing machine timers are in
the 1 hour range.  Sometimes, the motor is stopped during certain portions
of the cycle awaiting completion of some other operation (i.e., fill).

These controllers therefore consist of several parts:

* Timing motor.  A very small synchronous AC line operated motor with
  an integral gear train is most common.  Sometimes, the rotor and
  geartrain are in a sealed, easily replaceable unit - a little metal
  case that clamps within the pole pieces of the AC field magnet.  In
  other cases, it is a separate motor assembly or an integral part of
  the overall timer mechanism.

* Escapement (not present on all types).  This is a device which converts
  the continuous rotation of the timing motor to a rapid movement for each
  incremental cam position.  A common type is a movement every 45 seconds
  to the next position.  This assures that the make or break action of the
  switches is rapid minimizing arcing.

* Cam(s).  One or more cams made of fiber composite, plastic, or metal,
  are rotated on a common shaft.  There will be one set of switch contacts
  for each circuit that needs to be controlled.

* Switches.  These will either be exposed sets of contacts or enclosed
  'microswitches' which are operated by the cams.

Testing: If the controller is not working at all, check for power to the
motor. Listen for the sound of the motor parts rotating.  Check for gummed
up lubrication or broken parts.

If some of the circuits do not work, check the switches for dirty or worn
contacts or broken parts.

  6.30) Electronic controllers - simple delay or microprocessor based

These can range from a simple R-C (resistance-capacitance) circuit to
provide the time delay in a toaster to sophisticated microprocessor based
systems for programming of a coffee maker or microwave oven.

While generally quite reliable, bad solder connections are always a
possibility as well as failed parts due to operation in an environment
prone to temperature extremes.

Testing: Check for bad solder connections and connectors that need to
be cleaned and reseated.  Inspect for obviously broken or burned parts.
Test components for proper value.

For digital clock/programmers or  microprocessor based controllers, not
much else can be done without a schematic - which not likely to be easily

  6.31) Batteries - Alkaline, Lithium, Nickel-Cadmium, Lead-acid

More and more small appliances and power tools are cutting their
cords and going to battery power.  Although there are a large number
of battery types, the most common for power applications (as opposed
to hearing aids, for example) are:

* Alkaline - primary (non-rechargeable, for the most part), long shelf life,
  high energy density.

* Lithium - primary and secondary (rechargeable) available though most
  appliance applications (which are just beginning to develop) are not
  rechargeable.  Long shelf life, very high energy density.  Still quite

* Nickel Cadmium - most common rechargeable technology in cordless appliances
  and power tools.  However, relatively fast self discharge and on about
  half the capacity of a similar sized Alkaline.

* Lead-Acid - secondary type similar to the battery in your automobile
  but packaged in a totally sealed container which is virtually indestructible
  and leakproof.  Medium self discharge rate but will deteriorate if left
  discharged for an extended period of time.

See the chapter: "Batteries" for more information.

  6.32) AC adapters and chargers - wall 'warts' with AC or DC outputs

These wall adapters are used to power many small electronic devices and
appliances directly and/or to recharge their batteries.  They usually
plug directly into the wall socket and convert the 115 VAC (U.S.) to a
lower voltage - 3 V to 24 V AC or DC typical.  More sophisticated units
may actually be a switching power supply with smart electronic control of
battery charging and power management.   The following are typical types:

* AC output - 3 to 24 VAC (or more) at 50 mA to 3 A.  The only internal
  component is a power transformer which may include a thermal or ordinary
  fuse for protection.

* DC output - 3 to 24 VDC (or more, under load) at 50 mA to 1.5 A.  In
  addition to the power transformer, there is a rectifier, filter capacitor,
  and possibly a three terminal IC regulator (not that common).  Some type
  of protection will probably be built in as well.

* Universal/switching power supply - typically 6 to 18 VDC at .5 to 3 A.
  These will usually operate off of any voltage input from 90 to 240 VAC
  (or DC) and provide a well regulator output.  There will generally be 
  an internal fuse as well as overvoltage and overcurrent protection.

In some cases, a single adapter will put out multiple voltages.  See the
chapter: "AC Adapters and Transformers" for more information.

Chapter 7) AC Line and Battery Powered Household Appliances

  7.1) Table lamps

This is the most popular type of lighting for reading or general illumination.
The type described in this section takes normal 115 VAC light bulbs.

The common table lamp is just a light duty cordset, switch, and sockets
for one or more incandescent light bulbs.  In many cases, the switch and
socket are combined into one assembly.  In other designs, particularly
where more than one bulb can be lit independently (for example, a large
bulb up top and a night light in the base), a separate switch (rotary or
push-push) selects the light bulb(s) to be turned on.

For the most common combined switch and socket, there are several varieties
and these are all generally interchangeable.  Therefore, if you want to take
advantage of the added convenience of a 3-way bulb allowing low, medium, and
high illumination, it is a simple matter to replace the simple on-off
switch in your lamp with a 3-way switch (not to be confused with the 3-way
switches used in house wiring to control a single light fixture from 2 places).

Push-push, pull chain, and rotary switches are common for simple on-off
control.  The 3-way switches are usually of the rotary variety with
off-low-medium-high selected as the knob is rotated.  The 3-way bulb has
two filaments which can be switched on individually or in combination to
provide the 3 levels of illumination.

Dimmer sockets can often be substituted for the normal kind as long as
conventional incandescent bulbs (and not compact fluorescents) are to
be used.

Touch and even sound activated switch-sockets are also available though
my personal recommendation is to stay away from them.

Most common problems: burned out bulb, worn switch, bad plug or cord.
Where the light flickers, particularly if jiggling or tapping on the
switch has an effect, a bad switch is almost always the problem.  Switch
failure is more common when using high wattage bulbs but can occur just
due to normal wear and tear.

Replacements for most common switches and sockets are readily available at
large hardware stores, home centers, and electrical supply houses.  It is
best to take along the old switch so that an exact match (if desired) can
be obtained.  While the thread sizes for the screw on socket shells are
quite standard, some older lamps may have an unusual size.  For more
complicated switches with multiple sockets, label or otherwise record the
wiring.  If color coded, cut the wires so that the colors are retained
at both the lamp and switch ends.

  7.2) Rebuilding a basic table lamp

As noted in the Introduction, virtually any table lamp can be restored
to like-new electrical condition for a few dollars at most.  The following
is the detailed procedure for the majority of common table lamps found
in the U.S.

This is assumed to be the type of lamp which has a combination socket and
switch with a metal (brass-colored usually) outer shell.  It is your decision 
as to whether a simple on-off switch or a 3-way type is to be used - they are
usually interchangeable and a normal light bulb can be put into a 3-way socket
(two clicks of the knob will be needed to switch a normal light bulb on or off,
however).  You can also put a 3-way bulb into a normal socket but you will, of
course, only get one level of illumination (medium).  For lamps with lighted
bases, also see the section: "Lamps with night-light bulbs in their base".

You will need: (1) a new socket/switch of the appropriate type and (2) a
new cordset (if you want to replace this as well).  A polarized type plug
is desirable to minimize the possibility of shock when changing bulbs.  A
medium size straight blade screwdriver and wire strippers are the only
required tools.

First, remove and set aside any shade, frosted chimney, and other cosmetic

Unplug the lamp!!!

Examining the metal shell, you will note that it is in two pieces.  If you
look carefully, there will probably be indications of where firmly pressing
the top portion will allow it to be separated from the bottom part mounted
on the lamp.  These are usually near where the knob, button, or chain, enters
the switch.  Sometimes, a fine screwdriver blade will be useful to gently
pry the two halves apart.

With the top part removed, unscrew and disconnect two wires and remove
the switch.  If desired, loosen the set screw (if any) and unscrew the
bottom portion of the shell.  If you are simply replacing the switch, at
this point you would just attach the new one and reassemble in reverse
order.  Screw on the bottom of the new switch enough so that it is either
tight or until the threads are fully engaged but not pressing on or protruding
above the cardboard insulating disk in the bottom half of the shell.  If
the entire assembly is still loose, it should be possible to tighten hardware
on the bottom of the lamp to secure it against rotation.  Note: it is
important to do this to avoid eventual damage to the wires should the switch
move around significantly during normal use.

To replace the cordset, you may need to partially remove any felt pad
that may be glued to the base of the lamp.  Sometimes, it is possible to
cut off the old plug, attach the new cord to the end of these wires, and
pull it through.  However, in most cases, there will be a knot or other
strain relief in the original cord which will make this impossible (and
you will want to replicate this in the replacement as well).  Therefore,
if needed, carefully peel back the felt pad only enough to gain access to
the interior.  In some cases, just cutting a small X in the center will
allow sufficient access and this can be easily patched with a piece of
cloth tape.

Install the new cord in exactly the same way as the original with a knot
for a strain relief if needed.  If there was no strain relief to begin
with, adding a knot is a good idea if there is space for one in the base.
Snake the cord through to the top of the lamp.

Strip the ends of the wires to a length of about 1/2 inch and twist the
strands tightly together in a clockwise direction.  If you are using a
cordset with a polarized plug, identify the wire attached to the wide
prong (with a continuity checker or ohmmeter if it is not clearly marked
by a stripe on the insulation) and connect it to the silver colored screw.
Connect the wire attached to the narrow prong to the brass colored screw.
Always wrap in a clockwise direction.  See the section: "Attaching wires to screw terminals".

Confirm that there are no loose wire strands and that the insulation is
nearly flush with the screw to avoid possible shorts.  Pop the shell top
with its insulating cardboard sleeve over the switch and press firmly onto
the base.  There should be a very distinct click as it locks in place.

If needed, adjust the strain relief at the base of the lamp so that pulling
on the cord does not apply any tension to the wires attached to the switch.
Tighten the nut in the base of the lamp holding the entire assembly in place
if the socket is still loose and rotates easily.  Don't overdo it - the
supporting structure is often just a glass jar or something similar.  Put
a drop of Loctite, nail polish, Duco cement, or something similar - or a
second nut - on the threads to prevent the nut from loosening.  Use some
household cement to reattach the felt pad you peeled back earlier.

  7.3) Lamps with night-light bulbs in their base

These are the types of lamps where either the normal bulb on top or a smaller
one in the base (or both) can be turned on using a turn-key or pull-chain.

This is a standard, if somewhat unusual socket.  It is basically the same
as a 3-way type but with the extra connection going to the bulb in the base
of the lamp.  In the old days when sockets were assembled with screws instead
of rivets, it might have been possible to modify a new 3-way socket to provide
the extra connection.

An electrical supply parts distributor or lamp store should have what you need
or be able to order it for you.

Take note of the connections as you remove the old socket to avoid mistakes.
When routing the wires to the bulb in the base, avoid allowing the hot bulb
from contacting the insulation - the plastic stuff might melt (for a 7 W or
less wattage bulb and high temperature insulation is probably not an issue,

  7.4) High intensity lamps

These include several types but they all use a transformer to reduce the
115 VAC to something lower like 12-24 V.

Tensor(tm) (and their clones) high intensity lamps have been around for
over 30 years and are essentially unchanged today.  They use a low voltage
transformer producing 12-24 VAC along with a special high output light bulb
that looks similar to an automotive tail light.  However, it uses substantially
more current for the same voltage and puts out a much more intense, whiter
light.  These are not halogen lamps though their spectral characteristics are
similar since the filaments run hotter than normal incandescents - and have
shorter lives.

Some will have multiple levels of illumination based on selecting taps on
the transformer.  Normal dimmers may not work (and should not be used) with
these due to their transformer design - damage to the dimmer or lamp may
result and this may be a fire hazard.

Problems with Tensor lamps tend to center around the socket and switch.
These may fail due to overheating as a result of the high temperature and
high current operation.  Replacements are available but they may take some
effort to locate.  A replacement lamp may be cheaper.  (I often find complete
Tensor lamps in perfect operating condition at garage sales for around $2.

  7.5) Halogen lamps and fixtures

Halogen lamps share many of the design characteristics of high intensity
lamps in that they are designed for local high intensity lighting and use a
transformer usually (though some may use solid state voltage conversion
instead).  While some halogen lamps come with dimmers, some of the advantages
of the halogen cycle are lost if the bulbs are not run at full power.  The
worst case is where they are operated just below full power - too cool for
the halogen cycle to take place but hot enough for substantial filament
evaporation to occur.

Should the dimmer portion of such a fixture fail or become unreliable, it may
a blessing in disguise since the lamp will either run at full intensity or can
be easily rewired to do so by bypassing the electronics and just using the
on/off switch!

WARNING: halogen bulbs run extremely hot and are a serious fire hazard and
burn hazard if not properly enclosed.  When changing a halogen bulb, wait
ample time for the old one to cool or use an insulated non-flammable glove
or pad to remove it.  When installing the new bulb, make sure power is off,
and do not touch it with your fingers - use a clean cloth or fresh paper
towel.  If you do accidentally touch it, clean with alcohol.  Otherwise,
finger oils may etch the quartz and result in early - possibly explosive
failure - due to weakening of the quartz envelope.

  7.6) Safety guidelines for use of halogen lamps

These guidelines were prompted by a number of fires including some fatalities
that have been linked to improper use of halogen lamps - in particular the
high power torchiere variety of floor lamps.  However, the guidelines apply
to many other types of halogen lamps including work-lights, desk lamps, slide
and overhead projectors, and other lamps or fixtures where the bulb is not
entirely enclosed and thermally insulated from the exterior.

(Source: The Associate Press except as noted).

Safety groups recommend the following precautions for owners of halogen
torchere lamps with tubular bulbs:

* Place the lamps where they cannot be tipped over by children, pets, or
  strong drafts (away from open windows, for example).

* Never use halogen lamps in children's bedrooms or playrooms where combustible
  objects like stuffed toys may be accidentally placed on top of or next to

* Never use a replacement bulb of a higher wattage or of a different type
  than specified by the manufacturer.  Avoid bulbs larger than 300 W.

* Never attempt to replace or discard a bulb that is too hot to touch.

  Do not touch the new bulb with your fingers as the oils and acids may make
  them more prone to exploding.  Clean the bulb thoroughly with isopropyl
  alcohol after any accidental contact (--- sam).

* Never drape cloth over the lamp.

* Operate the lamps at less than maximum wattage on a dimmer whenever possible.

  Note that this may not result in maximum life but will be safer due to the
  lower temperature of the bulb (--- sam).

* Keep lamps away from elevated beds like bunk beds where the bedding may get
  too close to the bulb.

* Never use unprotected halogen lamps in locations like bathrooms where water
  may splash resulting in the bulb exploding (--- sam).

* Never operate lamps with their thermal or UV shields removed (--- sam).

  7.7) What causes a lamp to flicker?

Many things can cause the light bulb in a table lamp to flicker:

* Loose bulb(s) :-).

* Bad switch.  These do wear out particularly if multiple high wattage bulbs
  are being used.  If gently jiggling the switch results in flickering this
  is the most likely cause.

* Bad connections.  These could be anywhere but the most likely locations
  (where only a single lamp is involved) would be either at the screw
  terminals on the switch or from a plug that isn't making secure contact in
  the outlet - check it.

* Voltage fluctuations.  Occasional flickering when high wattage appliances
  kick in is not unusual especially if they are on the same branch circuit but
  could also be a symptom of other electrical problems like a loose Neutral
  connection - see the section: "Bad Neutral connections and flickering lights or worse".

  If a dimmer control is present, keep in mind that these are somewhat more
  sensitive to slight voltage fluctuations especially when set at low levels.
  You may simply not have noticed any flickering with a normal on/off switch.

  7.8) Touch lamp problems

Personally, I think touch lamps are one of the dumber uses of technology
to appear on this planet but that is just my opinion :-).

These are susceptible to damage from voltage surges or just plain old random
failures.  In addition, the current surge that often results at the instant
an incandescent bulb burns out (the bright flash) may blow the thyristor in
the electronics module.

If the lamp is stuck on, the thyristor is probably shorted.  The specific
part can be replaced but to be sure it is bad, some testing will be needed
and it is probably soldered in place.  However, if you have repaired an
ordinary lamp, you will be able to replace the entire module fairly easily.

If the lamp is stuck off, there could be a bad connection or bad bulb, or
the electronics module is defective.  Again, replacement is straightforward.

Erratic problems could be due to bad connections, dried up electrolytic
capacitors (especially if the electronics module is near the hot bulb), or
even external E/M interference (e.g., a dimmer or vacuum cleaner on the same

Some problems are of the following type:

"I have 2 touch lamps in the bed room and they are both plugged in to the
 same receptacle.  Every once in a while the lamps come on by themselves
 for no apparent reason.  Even more strange is that every so often just
 one lamp turns on by itself."

(From: Tim Moore (tmoore@interserf.net)).

These use a MOSFET type circuit to switch the lamps on and off. The circuit
is attached to the metal in the lamp base. When you touch it the impedance
changes ever so minutely but enough to change the MOSFET from off to on
and visa versa. My wife could never get our lamps to switch, she often
had to blow on her hand first to get it moist so it would make better
contact. Here is part of the problem. It takes a certain amount of
signal from the lamp base to switch the circuit. Electronic parts all
have acceptable ranges of operation and when put into identical circuits
they sometimes perform differently. One circuit might need a good hard
touch while the other might need only a slight touch. Power surges would
often switch one of my lamps, although it didn't happen often. A strong
radio signal could do it too. The bottom line is that these lamps are
not rocket science and can't be counted on as 100% reliable. Sorry,
that's the truth. You give up a little to get the convenience of just
having to touch them. I ended up removing mine - an electrical storm
wiped one out and wiped the other out a few years later. 

  7.9) Touch lamps and RF interference

While many people swear by touch lamps, nearly as many swear at them since in
addition to frequent failures (bulb burn-outs killing the triac, for example),
they can also be tempermental, cycling through their brightness settings
and/or turning on or off due to static electricity, power line transients
causing RFI, and stray pickup from the local ham rig.

(Portions from: John Evans - N0HJ (jaevans@codenet.net)).

Here is a fix my buddy, Ed, a fellow ham radio operator, has come up
with to solve this problem.

As usual it took 8 months and 10 minutes to fix.

Two parts: 1/4 watt, 1k Ohm resistor and 2.5 mH 1/2 watt size molded coil.
Connect in-line with the touch wire.

I send 2 or more watts from my rig.  My son works the CB.

You'll find it on when you get home.

So the darn thing is an oscillator which changes frequency when you touch it.
The circuit does the rest.  By adding the resistor/inductor pair, its
sensitivity is reduced and the problem disappears.

One more thing:  (Most important!), you won't hear interference FROM the
oscillator in the lamp anymore on your radio.

And don't open up the module inside the lamp base, you are wasting your time
there, and adding more work to glue the module back together.

Just Choke off the sense wire with the resistor and 2.5 mH choke.  You'll be

  7.10) Incandescent fixtures

A fixture is normally permanently mounted to a wall or ceiling.  However,
aside from not usually having a plug - being directly wired - they are
similar to table lamps in what is inside.

There will be one or more sockets for light bulbs - often all wired in
parallel so that all the bulbs come on at the same time.  For wall fixtures,
there may be a switch on the fixture though most often the switch is mounted
on the wall elsewhere.

Unlike table lamps where most of the heat rises from the bulb away from the
socket, mounting the sockets horizontally or inverted (base up) can result
in substantial heating and eventual deterioration of the socket and wiring.
Common problems relate to this type of problem - bad connections or brittle
wire insulation.  Replacement parts are generally available at home centers
and electrical supply houses.  Just make sure to kill power before working
on any fixture wired into your house's electrical system!

  7.11) Removing the base of a broken light bulb

Turn off power and double check!  Wear safety goggles to protect against
flying bits of glass.

Then use a pair of needlenose pliers or any other tool that will grip what
is left of the base to twist it free.  A piece of a raw potato may even work!

  7.12) Locating burnt out bulbs in series circuits

Christmas and other decorative lights are constructed as series strings
of low voltage light bulbs as shown below:

    Male o------O----O----O----O----O----O----O----O---+
    Plug                                               |

Or the following which permits several strings to be connected end-to-end:

            |             Bulbs                           |
    Male o--+---O----O----O----O----O----O----O----O---+  +--o Female
    Plug                                               |       Socket

Many variations on these are possible including multiple interleaved series
strings.  One of the bulbs in each circuit may be a flasher.  All newer light
sets must include a fuse as well.

In a series connected circuit, if one bulb burns out, all lights go out.  The
newer types include a device in each bulb which is supposed to mechanically
short out that bulb if it burns out.  However, these don't always work or you
may have a set that doesn't have this feature.

The following assumes a single series circuit - large light sets (e.g.,
perhaps 50 or more) will have multiple series strings so you will have
to identify the particular circuit that is bad.  If more than one bulb
is burnt out, this may further complicate matters.
To locate a burnt out bulb in a series string, you can use the binary search
approach: pull a bulb in the middle of the string.  Test the bulb and between
the power cord end and the middle for low resistance.  If these are ok, you
know the bad bulb is in the other half.  Then divide the 'bad' portion in half
and test one half of it and so forth.  For example, using this technique, you
will need to make at most 6 sets of measurements to locate a bad bulb in a 50
light set.

Sears, K-Mart, Radio Shack, among others sell inexpensive testers (e.g.,
Lite-Tester Plus, about $4).  These detect the electric field generated by
the (now floating) wire on the Hot side of the gap of the burnt out filament.
These will also locate open wires and blown fuses in the same manner.

I have also heard of bulb sets in which the individual bulbs are gas filled
in such a way that if the filament breaks, current flows across the gap
through the gas resulting in a faint glow in the burnt out bulb.  I don't
know if these things still exist.

WARNING: Do not be tempted to bypass a bad bulb with a wire.  This will reduce
the total resistance and increase the current to the remaining lamps shortening
their life.  Do this a few times, and the entire string will pop.  This is a
serious safety hazard especially on older light sets that may not have internal
fuses.  Some fuses look like lamps - replace only with an identical fuse - not
with a lamp!

  7.13) Comments on Christmas tree bulb/string repair

Original type of problem: No light but fuses are good and no obvious damage.

(From: Ken Bouchard (bouchard@ime.net)).

My advice, is trash them and go out and buy new ones.  After all, you can get
them typically around 5-10 bucks a set.

Then you have the old set to raid bulbs from, for the ones that blow out.

Quality control is not an issue when they build xmas lights.  One slight tug
of a wire, can break it, and the entire set goes dead.

First I assume you wiggled all the bulbs, often just a loose bulb causes this.
In the smaller type bulb sets the string is wired in sections, so one bulb
goes out, and every 4th or 5th one is dead.

The little bulbs were also designed, that if the filament breaks in the bulb
a piece of foil inside it shorts out that bulb so that the remaining lights
keep on working. This works up to a point, until more than 4-5 bulbs blow
out at once, then the remaining ones get too much voltage and blow out too.

Often the cheesy sockets get water in them and corrode, and/or the wires on
the bulb get twisted or broken.

They also use a cheap method of crimping the wiring together in these lights.
Most times you can find the broken wire, by inspecting, seeing where it goes
into the socket it pulls out easily.

Well avoid doing this when the set is live (heh...) unless you like the idea
of getting zapped.

  7.14) Controlling a fixture or outlet from multiple locations

Although the specific case of controlling a fixture or outlet from exactly
two locations is a special case of switches at more than 2 locations, each
is described separately since the former is much more common.

Should you care, these implement the multiple input XOR (exclusive OR) logic
function for controlling electrical devices.

Note: See the section: "Dimmer switches and light dimmers" if you would like
to have control of brightness of a lamp or fixture from multiple locations.

* For exactly two locations (say at the bottom and top of basement stairs), you
  will need a pair of what are known as 3-way switches.

  These are actually SPDT (Single Pole Double Throw) switches which look like
  ordinary wall switches but have 3 screws instead of 2.  Two of these screws
  will be the same color (usually brass) while the third will be different
  (darker copper or brown).  They may be marked as well.

  Note that a socket for a 3-way bulb for a lamp is not related to this - only
  the name is similar.

  Typical wiring for controlling a fixture or outlet from exactly two locations
  is as follows:

            Location 1         Location 2
             3-way SW     A     3-way SW          +---------+
                /o----------------o\              | Fixture |
    Hot o-----/                      \o-----------|   or    |--------o Neutral
                 o----------------o        Center | Outlet  | Shell
                          B               (brass) +---------+ (silver)

                                           /o---o                   o---o
  A 3-way switch connects either up  o---/         or down  o---o\        .
                                            o---o                  \o---o

  As usual, the brass screw on the fixture or outlet should be connected to
  the Hot side of the wiring and the silver screw to the Neutral side.

  Another common variation is shown below:

                                          Location 1           Location 2
                                           3-way SW    Rd :     3-way SW
                                    : Bk      /o------------------o\ 
        Hot o-------------------------------/          Wh :          \o---+
                                    :          o------------------o       |
                    +---------+     :                     :               |
                    | Fixture |     : Wh   Splice      Bk :               |
    Neutral o-------|   or    |---------------X---------------------------+
                    | Outlet  |     :     (Wirenut)       :
                    +---------+   14-2                  14-3

  Details may differ for your particular installation (like to which sides the
  Hot and Neutral are connected and/or particular wire colors used).

* For more than two locations (say at 3 doors to your dining room), you will
  need a combination of 3-way switches and 4-way switches.  Two of the 3-way
  type will be needed at the ends of the circuit (below) with 1 or more 4-way
  type in between.  Thus for 'n' switch locations, n-2 of the 4-way switches
  will be needed.

  4-way switches have 4 terminals arranged as two pairs.  In one position pair
  1 is connected to pair 2 straight through.  In the other position, the
  connections are interchanged.

  Typical wiring for controlling a fixture or outlet from 3 or more locations
  is as follows:

        Location 1     Location 2     Location 3
         3-way SW   A   4-way SW   A   3-way SW        +---------+
            /o------------o\ /o-----------o\           | Fixture |
  Hot o---/                 /               \o---------|   or    |---o Neutral
             o------------o/ \o-----------o    Center  | Outlet  | Shell
                    B              B           (brass) +---------+ (silver)

                                           o---o              o\ /o
  A 4-way switch connects either straight         or exchange   /   .
                                           o---o              o/ \o

  This can be extended to an arbitrary number of positions.

  As usual, the brass screw on the fixture or outlet should be connected to
  the Hot side of the wiring and the silver screw to the Neutral side.

  Note that a 4-way switch can be constructed from a DPDT (Double Pole Double
  Throw) type (e.g., toggle switch) as follows:

                    |              |
      A(in) o---------------+      |
                    |       |      |
                    +----o  o/ o-------+------o A(out)
                             :     |   |
                    +----o  o/ o---+----------o B(out)
                    |       |  DPDT    |
      B(in) o---------------+  toggle  |
                    |          switch  |

  For low voltage (non-house wiring) or panel mount applications, this may be
  easier than using actual 4-way switches (which are probably not available in
  small sizes).

The 3-way switches (at least the basic white, ivory, or brown toggle type)
can be found nearly anyplace that sells common electrical devices including
hardware stores and home centers.  You may have to look a little harder for
4-way switches as well as styles or colors to match your decor as these are
not as widely available.  However, a decent electrical supply house should
have all of these.

The wires marked A and B (sometimes called 'travelers') may be in a single
(Romex) cable and should be on the screws that are both the same color.

If you do use Romex with a black and white wire, put black tape on the
insulation at the ends of the white wire (or paint the ends black) to
indicate that this is a Hot wire and not a Neutral.  This is required by
Code but allows the use of this type of wire.

These diagrams represent one wiring arrangement.  Sometimes, there are other
slight variations.  For example, you might find the switches in the Neutral
instead of Hot portion of the wiring - however, this is not recommended.

  7.15) Identifying unmarked wiring for 3-way switch

(Also see the section: "Controlling a fixture or outlet from multiple locations".)

So you forgot to label the wires before you removed the old switch, huh? :-).

You have several options:

* It may be obvious from the way the box is wired as to which are the
  A/B pair.

* Use a tester to figure out which wire is which (see below).

* Interchange the different colored screw wire with one of the others.
  If this doesn't fix it, interchange the different colored screw wire
  with the other one.  As long as you have only touched the wires on the
  old switch, you cannot damage anything by doing this.

* Get an electrician.

Of course, kill power before touching or changing anything!

Here is one way to identify the proper wires more quickly than trial and error:

1. Identify the Hot wire.  With all 3 wires in each box disconnected and their
   ends exposed, use a tester between each one and the a earth ground (the
   box if metal and properly grounded).  With power on, only one of the 6
   wires will be live.

Now, turn off the power and confirm that it is off by retesting the hot wire
you identified above.

2. Connect the lone screw (the different or darker colored one) on one switch
   to this Hot wire.  Connect the same-color screws on the switch to the other
   two wires.  This should take care of one box.

3. With any luck, you should be able to connect the wires in the other
   box exactly the same way color wise.

(From: CodeElectric@Worldnet.att.net).

Check both boxes.  There will be a single Hot - that goes on the common of
the 3-way switch.  Put the other two wires on the other two screws.

Now, at the other switch, you will find one hot.  Put that on a screw, not
the common.  Switch the other switch, and you'll find another hot.  That is
the other traveler.  You've got one wire left,,, that's the other common.

In more detail:

First, shut off the power to the circuit.  Then remove the wires from the
switches.  Ignore the colors of the wires... there's too many combinations to
use so the colors won't mean anything.

Look closely at the switches.  You will find one screw different from the
other two.  It may be black, while the other 2 are gold, or may have the word
'common' printed near it.  This is, (duh!) the 'common' terminal.  The other
two are 'traveler' terminals.  Having identified the commons and travelers,
make sure your family knows you're working with live wires, and let them know
not to touch!!!!

Turn the power back on, and out of the six wires that came off of the two
switches, ONE of them will have power.        Once you find that one, turn the
power back off, and hook that one wire to the common terminal of a switch. 
Hook the other two wires in that box to the traveler terminals.  It doesn't
matter which one goes where.  Put the switch into the box, and place the
cover back on.        You're done with than switch.

Now turn the power back on, and check the remaining three wires.  One will be
hot.  Flip the first switch, and another will be hot.  These are your traveler
wires.  Turn the power back off, and hook those two wires to the two traveler
terminals on the second switch.  Again, it makes no difference which goes
where.  The final wire goes to the common terminal.  Button everything up, and
you should be done.

Turn the power back on, and you should be up and running.

  7.16) Dimmer switches and light dimmers

In the old days, a dimmer was a large high wattage rheostat put in series
with the light bulb.  These were both inefficient and producers of a lot
of heat.  Modern dimmers use a device called a triac (a type of thyristor)
which is a solid state switch to control illumination by turning the light
bulb on for only a part of each AC half-cycle (100 or 120 times a second
depending on where you live) as determined by the adjustment knob or slider.
Once switched on, it remains on for the remainder of the half-cycle:

* For low intensity, the current is switched on late in the half-cycle.

* For medium intensity, the current is switched on around the middle of the

* For high intensity, the current is switched on early in the half-cycle.

* For full intensity, the triac may be bypassed entirely.  There will probably
  be a detectable click position with the control set to full brightness if
  this is present.

Dimmers are available to replace standard wall switches and even for
use in place of the light bulb socket/switch in most table lamps.
However, nearly all of these are designed only for normal incandescent
light bulbs - not fluorescents, compact fluorescents, or high intensity
or halogen lamps (or any other type of lamp with a transformer).

(There are special dimmers for use with fluorescent lamps but these must
be specifically matched to the lamp type and wattage and their dimming
range is usually not very wide.  See: the fluorescent lamp information at http://www.misty.com/~don/light.html for a discussion of dimming techniques
and details on several relatively simple approaches that may work for your

Installation is generally very straightforward as there are only two wires
and polarity does not matter.  They simply replace the existing switch.

To assure long life, it is best to select a dimmer with a higher power rating
than your maximum load.  For example, if you are using four 100 W bulbs, a
600 W dimmer should be the minimum choice and one rated at 1000 W would be
better.  This is particularly true if halogen bulbs are used since these may
be harder on dimmers than normal types.  Further derating should be applied
where multiple dimmers are installed in the same outlet box resulting in
greater combined heating.  Higher wattage dimmer switches will have better
heat sinking as well which should result in the active components - the
thyristors - running cooler.  Dimmers are under the most stress and generate
the most heat when operating at about 50% output.

Dimmers may fail due to power surges, excess load, momentary fault (short)
at the instant of light bulb failure, or just plain old age.  A failed dimmer
will generally be stuck at full brightness since the thyristor will have
shorted out.  The mechanical on-off switch which is part of the dimmer
will probably still work.

* A power surge may result in a failed dimmer just like any other solid
  state device.

* Make sure you are nor overloading the circuit controlled by the dimmer.  Most
  common types are rated for 600 W maximum with heavy duty types up to 1200 W
  or more.  My advice is to not load them to more than 60-75% of their rating.

* When light bulbs burn out, there can be an instantaneous spike of high
  current due to the failure mechanism.  This may blow a fuse or trip a
  circuit breaker - but it may also blow out a dimmer control.

* Dimmers are not always of the highest quality design or construction and
  parts may run hot - ever touch the wall plate of a dimmer running at 50%
  power?  Long term reliability may not be that great.

It is not generally worth worrying about repair of a dimmer as they are so
inexpensive.  However, before replacement confirm that there is no actual
problem with the wiring (like a short circuit in the fixture) and that you
are not overloading the dimmer.

  7.17) Typical dimmer schematics

These are the type of common light dimmers (e.g., replacements for standard
wall switches) widely available at hardware stores and home centers.

While designed for incandescent or heating loads only, these will generally
work to some extent with universal motors as well as fluorescent lamps down
to about 30 to 50 percent brightness.  Long term reliability is unknown for
these non-supported applications.

CAUTION: Note that a dimmer should not be wired to control an outlet since it
would be possible to plug a device into the outlet which might be incompatible
with the dimmer resulting in a safety or fire hazard.

  7.18) Simplest dimmer schematic

The first schematic is of a normal (2-way) inexpensive dimmer - in fact this
contains just about the minimal number of components to work at all!

S1 is part of the control assembly which includes R1.

The rheostat, R1, varies the amount of resistance in the RC trigger circuit.
The enables the firing angle of the triac to be adjusted throughout nearly
the entire length of each half cycle of the power line AC waveform.  When
fired early in the cycle, the light is bright; when fired late in the cycle,
the light is dimmed.  Due to some unavoidable (at least for these cheap
dimmers) interaction between the load and the line, there is some hysteresis
with respect to the dimmest setting: It will be necessary to turn up the
control a little beyond the point where it turns fully off to get the light
to come back on again.

          Black o--------------------------------+--------+
                                                 |        |
                                              |  |        |
                                           R1 \  |        |
                                        185 K /<-+        |
                                              \  v CW     |
                                              |         __|__ TH1
                                              |         _\/\_ Q2008LT
                                              +---|>|   / |   600 V
                                              |   |<|--'  |
                                          C1 _|_  Diac    |
                                       .1 uF --- (part of |
                       S1                     |    TH1)   |
          Black o------/ ---------------------+-----------+

The parts that fail most often are the triac, TH1, or the combination
switch/control (S1/R1).

  7.19) 3-way dimmer schematics

There are at least two varieties of inexpensive 3-way style dimmer switches
which differ mainly in the switch configuration, not the dimmer circuitry.
You will probably have no reliable way of telling them apart without testing
or disassembly.

None of the simple 3-way dimmer controls permit totally independent dimming
from multiple locations.  With some, a dimmer can be installed at only one
switch location.  Fully electronic approaches (e.g., 'X10') using master
programmers and addressable slave modules can be used to control the intensity
of light fixtures or switch appliances on or off from anywhere in the house.
See the section: "True (electronic) 3-way (or more) dimmers".

However, for one simple, if inelegant, approach to independent dimming, see
the section: "Independent dimming from two locations - kludge #3251".

  7.20) Simple 3-way dimmer schematic 1

The schematic below is of one that is essentially a normal 3-way switch with
the dimmer in series with the common wire.  Only one of these should be
installed in a 3-way circuit.  The other switch should be a normal 3-way
type.  Otherwise, the setting of the dimmer at one location will always
affect the behavior of the other one (only when the remote dimmer is at its
highest setting - full on - will the local dimmer have a full range and

Note that the primary difference between this 3-way dimmer schematic and
the normal dimmer schematic shown above is the addition of an SPDT switch -
which is exactly what is in a regular 3-way wall switch.  However, this
dimmer also includes a choke (L1) and capacitor (C2) to suppress Radio
Frequency Interference (RFI).  Operation is otherwise identical to that
of the simpler circuit.

This type of 3-way dimmer can be used at only one end of a multiple switch
circuit.  All the other switches should be conventional 3-way or 4-way types.
Thus, control of brightness is possible only from one location.  See the
section: "True (electronic) 3-way (or more) dimmers" for reasons for thistrue
restriction and for more flexible approaches.

   Red 1 o--------o
                 S1   o----+------------+-----------+
                           |            |           |
   Red 2 o--------o        |         R1 \  ^ CW     |
                           |      220 K /<-+        |
                           |            \  |        |
                           |            |  |        |
                           |            +--+        |
                           |            |           |
                           |         R2 /           |
                       C2 _|_      47 K \           |
                  .047 uF ---           /         __|__ TH1
                           |            |         _\/\_ SC141B
                           |            +---|>|   / |   200 V
                           |            |   |<|--'  |
                           |        C1 _|_   D1     |
                           |   .062 uF ---  Diac    |
                           |            |           |
   Black o-----------------+---CCCCCC---+-----------+
                         40 T #18, 2 layers
                       1/4" x 1" ferrite core 

The parts that fail most often are the triac, TH1, or the combination
switch/control (S1/R1).

  7.21) Simple 3-way dimmer schematic 2

The schematic below is of a 3-way dimmer with a slightly more complex
switching arrangement such that when the local dimmer is set to full on or
full off, it is bypassed.  (If you ignore the intermediate dimming range of
the control, it behaves just like a normal 3-way switch.)  With this scheme,
it is possible to have dimmers at both locations without the dimmer
circuitry ever being in series and resulting in peculiar behavior.

Whether this is really useful or not is another story.  The wiring would be
as follows:

              Location 1             Location 2
             3-way Dimmer      A    3-way Dimmer     +---------+
                  /o----------------------o\         |  Lamp   |
    Hot o------o/    Silver 1     Silver 2   \o------|   or    |-----o Neutral
           Brass   o----------------------o   Brass  | Fixture |
                     Silver 2  B  Silver 1           +---------+

(If dimming interacts, interchange the A and B wires to the silver screws at
one dimmer).

This one uses a toggle style potentiometer where the up and down positions
operate the switches.  Therefore, it has 3 states: Brass to Silver 1 (fully
up), dim between Brass and Silver 1 (intermediate positions), and Brass to
Silver 2 (fully down).

                        Br  /o---o            Br   o---o          Br/\/o---o
  3-way dimmer is up o---o/   S1   or down o---o\  S1    or Dim o---o  S1
                             o---o                \o---o               o---o
                              S2                   S2                  S2

However, it is still not possible to have totally independent control - local
behavior differs based on the setting of the remote dimmer (details left as
an exercise for the reader).

Like the previous circuit, this dimmer also includes a choke (L1) and
capacitor (C3) to suppress Radio Frequency Interference (RFI).  It is just
a coincidence (or a matter of cost) that the 3-way dimmers have RFI filters
and the 2-way type shown above does not.

  Silver 1 o---+----------------+--------------------+-----------+
               |                |                    |           |
               |                |                 R1 \  ^ Up     |
               |                |              150 K /<-+        |
               |                |                    \  |        |
               |                |                    |  |        |
               |                |          +---------+--+        |
               |                |          |         |           |
               |            C3 _|_         |      R2 /           |
               |               ---         |    22 K \           |
               |                |          |         /         __|__ TH1
               |                |      C2 _|_        |         _\/\_ 
               |                | .047 uF ---        +---|>|   / |   200 V
           Up \                 |          |         |   |<|--'  |
               |                |          |     C1 _|_   D1     |
               |                |          |.047 uF ---  Diac    |
               |                |          |         |           |
               |  Dim  o--------+---CCCC---+---------+-----------+
               |     /               L1
     Brass o---+---o               12T #18
                           1/4" x 1/2" ferrite core
                 Down  o         
  Silver 2 o-----------+

The parts that fail most often are the triac, TH1, or the combination
switch/control (S1/S2/R1).

  7.22) True (electronic) 3-way (or more) dimmers

The objective is to be able to control a single fixture from multiple locations
with the capability of dimming as well as just power on/off.

The simple type of 3-way dimmers are just a normal dimmer with a 3-way instead
of normal switch.  This allows dimming control from only one location.  The
other switches in the circuit must be conventional 3-way or 4-way type.

Connecting conventional dimmers in series - which is what such a hookup would
require - will not really work properly.  Only if one of the dimmers is set
for full brightness, will the other provide full range control.  Anywhere in
between will result in strange behavior.  The other dimmer may have a very
limited range or it may even result in oscillations - periodic or chaotic
variations in brightness.  The safety and reliability of such an arrangement
is also questionable.

True 3 way dimmers do exist but use a more sophisticated implementation
than just a normal dimmer and 3-way switch since this will not work with
electronic control of lamp brightness.  One approach is to have encoder knobs
(similar to those in a PC mouse) or up/down buttons at each location which
send pulses and direction info back to a central controller.  All actions
are then relative to the current brightness.  A low cost microcontroller or
custom IC could easily interface to a number, say up to 8 (a nice round
number) - of control positions.  The manufacturing costs of such a system
are quite low but due to its specialty nature, expect that your cost will
be substantially higher than for an equivalent non-dimmable installation.

If control of intensity at only one of the locations is acceptable, a
regular dimmer can be put in series with the common of one of the normal
3-way switches.  However, your brightness will be set by that dimmer alone.
See the section: "Typical dimmer schematics".

An alternative is to use X-10 technology to implement this sort of 
capability.  This would likely be more expensive than a dedicated
multi-way switch control but is more flexible as well.  X-10 transmits
control information over the AC lines to select and adjust multiple
addressable devices like lamps and appliances.

However, for the adventurous, see the section: "Independent dimming from two locations - kludge #3251".

  7.23) Independent dimming from two locations - kludge #3251

Here is a scheme which will permit dimming with independent control from two
locations.  Each location will have a normal switch and a dimmer knob.  The
toggle essentially selects local or remote but like normal 3-way switches, the
actual position depends on the corresponding setting of the other switch:

                 Location 1       Location 2
           +--------+  4-way SW    3-way SW
Hot o--+---| Dimmer |----o\ /o--------o\            +---------+
       |   +--------+      /            \o----------| Fixture |------o Neutral
       |              +--o/ \o--------o      Center +---------+ Shell
       |              |                      (brass)           (silver)
       |              |            +--------+
       |              +------------| Dimmer |--+
       |                           +--------+  |

As usual, the brass screw on the fixture or outlet should be connected to the
Hot side of the wiring and the silver screw to the Neutral side.

The dimmers can be any normal knob or slide type with an off position.

Note that as drawn, you need 4 wires between switch/dimmer locations.
4-way switches are basically interchange devices - the connections
are either an X as shown or straight across.  While not as common as
3-way switches, they are available in your favorite decorator colors.

If using Romex type cable in between the two locations, make sure to tape or
paint the ends of the white wires black to indicate that they may be Hot as
required by Code.

And, yes, such a scheme will meet Code if constructed using proper wiring

No, I will not extend this to more than 2 locations!

Also see the section: "Controlling a fixture or outlet from multiple locations".

CAUTION: However, note that a dimmer should not be wired to control an
outlet since it would be possible to plug a device into the outlet which
might be incompatible with the dimmer resulting in a safety or fire hazard.

  7.24) How do touch dimmers work?

(From: Neil).

Touch dimmers work in a couple of different ways, depending on the IC used.
Simple ones, such as those in the cheap 'touch lamps' that you find for sale
on market stalls, etc. normally have three or four preset brightness levels
and an OFF setting, which are operated sequentially: touch once for full
brightness, again to dim slightly, again to dim a bit more, etc, until the OFF
setting is reached. The next touch will then bring the lamp to full

The better (and more expensive) units, such as the touch dimmer switches that
are sold as direct replacements for conventional light switches, are similar,
but have many more steps. A single touch will usually bring the lamp to full
brightness, while keeping your finger in contact with the touch plate will
slowly dim the lamp. You just remove your finger when the lamp is at the
required brightness level.

Both kinds of touch dimmer have three basic parts;

1. A touch sensor - this normally works by picking up mains hum from the
   touch plate, and rectifying it in a high-gain amplifier.

2. A ramp generator - normally in the form of a digital counter with DAC

3. A mains power control element - Generally a thyristor or triac. In some
   designs, this is encapsulated within the IC, while in others it is a
   discrete component.

Most touch dimmers can be operated by standard push-button switches as well as
a touch plate, and many can be adapted for remote control.

There are a number of specially designed IC's available for touch dimmers,
notably the HT7704B ,a four-step device for touch lamps as described above,
and the SLB0586A, which is the other kind, with facilities for remote control.

  7.25) Light dimmers and interference with radio or TV

Due to the sharp edges on the power supplied by a cheap light dimmer, Radio
Frequency Interference (RFI) may be conducted back down the wiring directly to
other appliances and/or radiated through space as well.  Effects will include
noise bars in the picture on some TV channels and/or a buzz in the audio
across portions of the AM radio band.

Better light dimmers will include a bypass capacitor (e.g., .01 uF, 1KV)
and a series inductor to suppress RFI but these components were often left
off in basic models.  The FCC has tightened up on their regulations around
1992 so replacing older dimmer switches with newer ones may be the easiest

Installing in-line power line filters may work but other options like
replacing all your house wiring with metal conduit, or only listening to FM
radio are probably not realistic!

  7.26) Can I use a dimmer to control transformer operated low voltage lighting?

It is very tempting to try using a common light dimmer to control devices
using power transformers.  Will this work?

There really is no definitive answer.  It is generally not recommended
but that doesn't mean it won't work perfectly safely in many instances.

However, in principle this may be dependent on what is on the secondary
side - a transformer appears more inductive when it is lightly loaded - and
on the design of your particular dimmer.

It could blow the dimmer or result in the dimmer simply getting stuck at
full power for some or all of the control range since the inductive load
will cause the current to continue flowing even after the voltage has gone
to zero and the thyristor should shut off.  If it works reliably in your
situations, then this is not a problem.  Again, it may be load dependent.

It probably will result in more audible noise from the transformer but this
is probably harmless except to your sanity.

The only safety issues I can think of and these relate to the transformer
running hotter than normal as a result of core saturation.  This might
happen at certain settings if the thyristor is not switching at the same
point on the positive and negative half cycles.  There would be a net DC
current flow through the transformer which is not good,  If the thyristor
were to fail in such a way that it only triggered on one half cycle, very
large DC current could flow.  However, a suitably rated fuse or circuit
breaker and thermal cutout should handle both these situations.

Note: If your dimmer uses an SCR instead of a triac, this will result in
immediate and catastrophic failure. An SCR results in a DC output.  However,
full range dimmers usually use triacs.

The bottom line: I cannot provide any guarantees.

  7.27) Flashlights and lanterns

Battery operated flashlights (torches for those on the other side of the Lake)
and lanterns are among the simplest of appliances.  We probably all have a box
or drawer full of dead flashlights.

The most common problem after dead batteries is very often damage due to
leaky batteries.  Even supposedly leak-proof batteries can leak.  Batteries
also tend to be prone to leaking if they are weak or dead.  Therefore,
it is always a good idea to remove batteries from any device if it is not
to be used for a while.  How to assure the batteries will be with the
flashlight?  Put them in separate plastic bags closed and fastened with
a twist tie.

Test the batteries with a multimeter - fresh Alkalines should measure 1.5 V.
Any cell that measures less than about 1.2 V or so should be replaced as they
will let you down in the end.  On a battery tester, they should read well into
the green region.

Check the bulb with a multimeter on the ohms scale - a bad bulb will test
open.  Bulbs may fail from use just like any other incandescent lamp or
from a mechanical shock - particularly when lit and hot.  Replacement bulbs
must be exactly matched to the number and type of batteries (cells).  A
type number is usually stamped on the bulb itself.  There are special
halogen flashlight bulbs as well - I do not really know how much benefit
they provide.

The switches on cheap flashlights are, well, cheaply made and prone to
unreliable operation or total failure.  Sometimes, bending the moving
metal strip a bit so it makes better contact will help.

Clean the various contacts with fine sandpaper or a nail file.

If a flashlight has been damaged as a result of battery leakage, repair
may be virtually impossible.

High quality flashlights are another matter.  Maglights(tm) and similar
units with machined casings and proper switches should last a long time
but the same comments apply to batteries - store them separately to avoid
the possibility of damage from leakage.  Keep a spare bulb with each of
these - the specialty bulbs may be harder to find than those for common
garbage - sorry - flashlights.

Rechargeable flashlights include a NiCd or lead-acid battery (one or more
cells in series) and the recharging circuitry either as part of the unit
itself or as a plug-in wall adapter or charging stand.  See the sections:
"Battery chargers" and "Typical rechargeable flashlight schematics" for more

  7.28) Typical rechargeable flashlight schematics

Here are circuit diagrams from several inexpensive rechargeable flashlights.
These all use very 'low-tech' chargers so battery life may not be as long as
possible and energy is used at all times when plugged into an AC outlet.

  7.29) First Alert Series 50 rechargeable flashlight schematic

This one is typical of combined all-in-one units using a lead-acid battery
that extends a pair of prongs to directly plug into the wall socket for

It is a really simple, basic charger.  However, after first tracing out the
circuit, I figured only the engineers at First Alert knew what all the diodes
were for - or maybe not :-).  But after some reflection and rearrangement of
diodes, it all makes much more sense:  C1 limits the current from the AC line
to the bridge rectifier formed by D1 to D4.   The diode string, D5 to D8 (in
conjunction with D9) form a poor-man's zener to limit voltage across BT1 to
just over 2 V.

The Series 50 uses a sealed lead-acid battery that looks like a multi-cell
pack but probably is just a funny shaped single cell since its terminal voltage
is only 2 V.

Another model from First Alert, the Series 15 uses a very similar charging
circuit with a Gates Cyclon sealed lead-acid single cell battery, 2 V, 2.5
A-h, about the size of a normal Alkaline D-cell.

WARNING: Like many of these inexpensive rechargeable devices with built-in
charging circuitry, there is NO line isolation.  Therefore, all current
carrying parts of the circuit must be insulated from the user - don't go
opening up the case while it is plugged in!

                                             2V LB1  Light
                                           1.2A +--+ Bulb    S1
                                       +--------|/\|----------o/ o----+
            _ F1   R3         D3       |        +--+                  |
   AC o----- _----/\/\---+----|>|--+---|----------------------+       |
          Thermal  15    |    D2   |   |                 4A-h |       |
           Fuse          | +--|>|--+   |         BT1 - |+ 2V  |       |
                         | |  D4       +--------------||------|-------+
                         +----|<|--+   |               |      |       |
                           |  D1   |   |  D8   D7   D6   D5   |  D9   |
          |        |                                                  |
          |        /                                                  |
         _|_ C1    \ R1                                               |
         --- 2.2uf / 100K                                             |
          |  250V  \                                                  |
          |        |               R2          L1  LED                |
   AC o---+--------+--------------/\/\-----------|<|------------------+
                                 39K 1W       Charging

  7.30) Black & Decker Spotlighter Type 2 rechargeable flashlight

This uses a 3 cell (3.6 V) NiCd pack (about 1 A-h).  The charging circuit is
about as simple as it gets!

         11.2 VRMS                                +---------------o/ o----+
  AC o-----+ T1       R1      LED1         D1     |  +| | | -             |
            )|| +----/\/\-----|>|---->>----|>|----+---||||||---+          |
            )||(      33    Charging     1N4002       | | |    |  KPR139  |
            )||(      2W                           BT1         |    LB1   |
            )||(                                   3.6V, 1 A-h |    +--+  |
            )|| +-------------------->>------------------------+----|/\|--+
  AC o-----+                                             Light Bulb +--+

        |<------- Charger ---------->|<---------- Flashlight ----------->|

I could not open the transformer without dynamite but I made measurements of
open circuit voltage and short circuit current to determine the value of R1.
I assume that R1 is actually at least in part the effective series resistance
of the transformer itself.

Similar circuits are found in all sorts of inexpensive rechargeable devices.
These have no brains so they trickle charge continuously.  Aside from wasting
energy, this may not be good for the longevity of some types of batteries (but
that is another can of worms).

  7.31) Brand Unknown (Made in China) rechargeable flashlight schematic

This is another flashlight that uses NiCd batteries.  The charger is very
simple - a series capacitor to limit current followed by a bridge rectifier.

There is an added wrinkle which provides a blinking light option in addition
to the usual steady beam.  This will also activate automatically should there
be a power failure while the unit is charging if the switch is in the 'blink'

With S1 in the blink position, a simple transistor oscillator pulses the light
with the blink rate of about 1 Hz determined by C2 and R5.  Current through R6
keeps the light off if the unit is plugged into a live outlet.  (Q1 and Q2 are
equivalent to ECG159 and ECG123AP respectively.)

            R1          D1                 R3   LED1
    AC o---/\/\----+----|>|-------+---+---/\/\--|>|--+    D1-D5: 1N4002
            33    ~|    D2        |+  |   150        |
           1/2W    +----|<|----+  |   |       R4     |  D5
                        D3     |  |   +------/\/\----+--|>|--+
              C1   +----|>|----|--+   |    33, 1/2W          |   LB1 2.4V
            1.6uF ~|    D4     |      |   | |                |   +--+ .5A
    AC o--+---||---+----|<|----+--+---|--||||--------------+-+---|/\|----+
          |  250V  |              |-  | - | |+             |     +--+    |
          +--/\/\--+              |   |   BT1      + C2 -  |      R5     |
              R2                  |   |  2.4V    +---|(----|-----/\/\----+
             330K                 |   |          |  22uF   |     10K     |
                                  |   |    R6    |       |/ E            |
                                  |   +---/\/\---+-+-----| Q1            |
                                  |       15K      |     |\ C  +---------+
                                  |                /  C327 |   |         |
                                  |             R7 \   PNP |   |   1702N |
                                  |           100K /       |   |   NPN |/ C
                                  |                \       +---|-------| Q2
                                  |      On        |           |       |\ E
                                  |   S1 o---------|-----------+         |
                                  +----o->o Off    |                     |
                                    Blink/Power Fail

  7.32) Makeup mirrors

There are a simple movable mirror with incandescent or fluorescent lighting
built in.

Replacing incandescent light bulbs can usually be done without disassembly.
The bulbs may be of the specialty variety and expensive, however.

When a unit using fluorescent bulbs will no longer come on, the most likely
cause is a bad bulb.  However, replacement may involve disassembly to fain
access.  Where two bulbs are used, either one or both might be bad.  Sometimes
it will be obvious which is bad - one or both ends might be blackened.  If
this is not the case, replacement or substitution is the only sure test.  These
**will** be expensive $7-10 is not uncommon for an 8 inch fluorescent bulb!

Other possible problems: plug, cord, switch, light bulb sockets.

  7.33) Chandeliers

A chandelier is simply an incandescent light fixture with multiple sockets.
No matter how fancy and expensive, the wiring is usually very simple - all
the sockets are connected in parallel to a cord which passes through the
chain to a ceiling mounted electrical box.

If none of the lights come on, check for a blown fuse or circuit breaker,
bad wall switch or dimmer, a bad connection in the ceiling box or elsewhere
in the house wiring, or a bad connection where the cord is joined to the
individual socket wires.

Where only one bulb does not light - and it is not a burned out bulb - a
bad socket, loose wire connection at the socket, or bad connection at the
point where the wires are joined (Wire Nuts(tm) or crimps) is likely.

  7.34) Portable fans and blowers

These consist of a cordset, switch, and AC motor.  Oscillating fans add
a gearbox to automatically swivel the fan to direct air in more than one
direction.  Most are of the bladed variety though some small types might
use a squirrel cage type centrifugal blower.

There are two kinds of problems: totally dead or stuck/sluggish.

A totally dead fan can be the result of several possible causes:

* Bad cord or plug - these get abused.  Test or substitute.

* Bad power switch - bypass it and see if the fan starts working or test
  with a continuity checker or multimeter.  Sometimes, just jiggling it
  will confirm this by causing the fan to go on and off.

* Open thermal fuse in motor - overheating due to tight bearings or a motor
  problem may have blown this.  Inspect around motor windings for buried
  thermal fuse and test with continuity checker or multimeter.  Replacement
  are available.  For testing, this can be bypassed with care to see if the
  motor comes alive.

* Burned out motor - test across motor with a multimeter on the low ohms
  scale.  The resistance should be a few Ohms.  If over 1K, there is a
  break in the motor winding or an open thermal fuse.  If there is no fuse
  or the fuse is good, then the motor may be bad.  Carefully inspect for fine
  broken wires near the terminals as these can be repaired.  Otherwise, a
  new motor will be needed.  If the motor smells bad, no further investigation
  may be necessary!

* Bad wiring - check for broken wires and bad connections.

As always, your continuity checker or multimeter on the low ohms scale
is your best friend and can be used to trace the wiring from the wall plug
through all components of the appliance.

Sluggish operation can be due to gummed up lubrication in the motor or any
gears associated with an automatic oscillating mechanism.  Disassemble,
thoroughly clean, and then lubricate the motor bearings with electric motor
oil.  Use light grease for the gearbox but this is rarely a problem.

A noisy fan may be due to dry motor or other bearings or loose hardware
or sheetmetal.  Disassemble, clean, and lubricate the motor or gearbox
as above.  Inspect for loose covers or other vibrating parts - tighten
screws and/or wedge bits of wood or plastic into strategic locations to
quiet them down.  

Damaged fan blades will result in excessive vibration and noise.  These
may be easily replaceable.  They will be attached to the motor shaft with
either a large plastic 'nut' or a setscrew.  However, locating a suitable
set of blades may be difficult as many cheap fans are not made by well
known companies.

  7.35) Computer power supply (and other) fans

Virtually all of these use brushless DC motors with stationary coils and a
rotating multipole magnet which is part of the blade assembly.  Most common
problems are gummed up lubrication or worn bearings - especially for the cheap
sleeve bearing variety found in most PCs.  Occasionally, an electronic failure
will result in a dead spot or other problem.

Ball bearing fans rarely fail for mechanical reasons but if the bearings
become hard to turn or seize up, replacement will usually be needed.  (Yes,
I have disassembled ball bearings to clean and relube THEM but this used only
as a last resort.)

WARNING: For power supply fans, be aware that high voltages exist inside the
power supply case for some time (perhaps hours) after the unit is unplugged.
Take care around the BIG capacitors.  If in doubt about your abilities, leave
it to a professional or replace the entire power supply!

The only type of repair that makes sense is cleaning and lubrication.  Else,
just replace the fan or power supply.  It isn't worth troubleshooting
electronic problems in a fan!

If you want to try to clean and lubricate the bearings, the blade assembly
needs to be removed from the shaft.  There should be a little clip or split
washer holding it on.  This is located under a sticker or plastic plug on the
center of the rotating blade hub.  Once this fastener has been removed, the
blades will slide off (don't lose the various tiny spacers and washers!)

Thoroughly clean the shaft and inside the bushings and then add just a couple
drops of light oil.  Also, add a few drops of oil to any felt washers that may
be present as an oil reservoir.

Reassemble in reverse order making sure the tiny washers and spacer go back
in the proper positions.

How long this lasts is a crap shoot.  It could be minutes or years.

Replacement fans are readily available - even Radio Shack may have one that
is suitable.  Nearly all run on 12 VDC but some small CPU fans may use 5 VDC.
While current ratings may vary, this is rarely an issue as the power supply
has excess capacity.  Air flow rates may also vary depending on model but are
usually adequate for use in PCs.

  7.36) Speed control of DC fans

The small fans used in computers and peripherals usually run on 5, 12 (most
common) or 24 VDC.  Most of the time, their speed and air flow are fine for
the application.  However, is it possible to vary it should the need arise?

Usually, the answer is a qualified 'yes'.  Except for some that are internally
regulated or thermostatically controlled, the speed is affected by input
voltage.  It is likely that the fan will run on anywhere from .5 to 1.25 times
the nominal input voltage though starting when it is near the low end of this
range may need some assistance.

A universal DC wall adapter, adjustable voltage regulator, or (variable)
series power resistor can provide this control.  For example:

                     25, 2 W        + +--------+ -
    +12 VDC o-----+---/\/\---+--------| DC FAN |----o Gnd
                  |   +      |        +--------+
                  +----|(----+      12 VDC, .25 A
                    10,000 uF
                      25 V

The 25 ohms power resistor should reduce the speed of this fan by about 25 to
30 percent.  The capacitor provides full voltage for a fraction of a second to
assure reliable starting.

  7.37) Speed control of small AC fans

The following comments should also apply to many other types of appliances
using small AC motors.

These small shaded pole fans will work just fine on a Variac.  Any speed you
want, no overheating, etc.  I had done this with all sorts of little computer
cooling fans as well as larger (remember those old DEC PDP-11 rack fans?).

Small triac based speed controls like those used for ceiling fans may also
work.  Even light dimmers will *probably* work for medium size fans or banks
of fans though I cannot guarantee the reliability or safety of these.  The
problem is that small induction motors represent a highly inductive loads for
the light dimmer circuitry which is designed for a resistive load.  I have
achieved a full range of speeds but over only about 1/4 to 1/2 of the rotation
of the control knob.  There is some buzz or hum due to the chopped waveform.

However, from my experiments, light dimmers may have problems driving a single
small fan.  If the load is too small, the result may be a peak in speed (but
still way less than normal) at an intermediate position and the speed actually
much lower when on full, or reduced speed even on full.  In this case, adding
a resistive load in parallel with the motor - a light bulb for example - may
improve its range.  It adds a sort of quaint look as well! :-)

If you do opt for a solid state speed control, make sure you include a fuse
in the circuit.  A partial failure of the triac can put DC through the motor
which would result in a melt-down, lots of smoke, or worse.

The reason these simple approaches will work for these AC motors is that they
are high slip to begin with and will therefore have a high range of speed vs.
input voltage.  The only concern is overheating at some range of lower speeds
due to reduced air flow.  However, since these fans are normally protected even
against stall conditions, I wouldn't expect overheating to be a problem - but
confirm this before putting such fans into continuous service.

If all you need to do is provide a fixed, reduced speed for a bank of similar
AC fans, try rewiring them as two sets of parallel connected fans in series.
The result will be 1/2 the normal line voltage on each fan motor which may
provide exactly the speed you want!  The extension to more than 2 sets of fans
is left as an exercise for the student :-).

  7.38) Ceiling fans

While the original slow rotating ceiling mounted fan predates the widespread
use of airconditioning, there is a lot to be said for the efficiency,
effectiveness, and silence of this technology - not to mention the ambiance.

A ceiling fan is just an induction motor driving a set of blades.  Multiple
taps on the motor windings in conjunction with a selector switch provides
speed control for most inexpensive fans.  Better units include a solid state
motor speed control.

The light often included with the fan unit is usually just an incandescent
fixture with 1-5 bulbs and a switch.  This may be a simple on-off type,
a selector to turn on various combinations of bulbs, or a dimmer with
continuous or discrete control of illumination.

WARNING:  Always check mechanical integrity of fan mounting when installing
or servicing a ceiling fan.  Original design and construction is not always 
as fail-safe as one might assume.  Double check for loose nuts or other
hardware, adequate number of threads holding fan to mounting, etc.  These
have fallen without warning.  Only mount in ceiling boxes firmly anchored
to joists - not just hanging from the ceiling drywall!  Check that the
fan is tight periodically.  The constant vibration when running, slight as
it is, can gradually loosen the mounting hardware.  Furthermore, if pull
chain type switches are used for the fan or light, constant tugging can also
tend to loosen the entire fan.

Failures of ceiling fans can be divided into electrical and mechanical:


* No power - Use a circuit tester to determine if power is reaching the
  fan.  Check the fuse or circuit breaker, wall switch if any, and wire
  connections in ceiling box.

* Bad switch in fan - with power off, check with a continuity tester.  If
  wiring is obvious, bypass the switch and see if the fan comes alive.
  Jiggle the switch with power on to see if it is intermittent.  For
  multispeed fans, exact replacements may be required.  For single speed
  fans, switches should be readily available at hardware stores, home
  centers, or electrical supply houses.

* Bad or reduced value motor start/run capacitor.  This might result in
  slower than normal speed or lack of power, a fan that might only start
  if given some help, or one that will not run at all.

  For an existing installation that suddenly stopped working, a bad cap is
  a likely possibility.  An induction motor that will not start but will
  run once started by hand usually indicates a loss of power to the starting
  (phase) winding which could be an open or reduced value capacitor.

  This is probably a capacitor-run type of motor where the capacitor provides
  additional torque while running as well.  Therefore, even starting it
  by hand with the blades attached might not work.  With the blades removed,
  it would probably continue to run.  Of course, this isn't terribly useful!

* Bad motor - if all speeds are dead, this would imply a bad connection
  or burned winding common to all speeds.  There might be an open thermal
  fuse - examine in and around the motor windings.  A charred smelly
  motor may not require further testing.  A partially shorted motor may
  blow a fuse or trip a circuit breaker as well or result in a loud hum
  and no or slow operation as well.


* Noise and/or vibration - check that fan blades are tight and that any
  balance weights have not fallen off.  Check for worn or dry bearings.
  Check for sheetmetal parts that is loose or vibrating against other parts.
  Tighten screws and/or wedge bits of plastic or wood into strategic spots
  to quiet it down.  However, this may be a symptom of an unbalanced fan,
  loose fan blade, or electrical problems as well.  Check that no part of
  the rotating blade assembly is scraping due to a loose or dislodged

* Sluggish operation - blades should turn perfectly freely with power off.
  If this is not the case, the bearings are gummed up or otherwise defective.
  Something may be loose and contacting the casing.  (This would probably
  make a scraping noise as well, however).

  7.39) Lubricating ceiling fans

(From: Chris Chubb (cchubb@ida.org)).

I use synthetic transmission lube, 80-130 (manual gearbox, not automatic
transmission fluid which is very thin --- sam).  I imagine that any similar
lubricant, synthetic or not, would work as well, but the synthetic flows down
in better and works well.

Do not use WD-40, 3-in-1 oil or any other lightweight oil. Motor oil is good
as well, but it does not stick to the bearings as well.  DO NOT use automatic
transmission fluid - extremely thin.

Grease would be perfect, white lithium, divine!  But, getting the grease
down into the bearings would be very difficult.

Just about three or four drops should be all it takes. Getting it
on the lower bearings of the ceiling fan will be tough. I have an
oil can that I pump a drop to the tip of, then hold it against the 
bearings until they wick the oil inside. This is very slow. It takes
about 15 minutes per fan to oil, clean the top of the blades, oil
a little around the hanging ball, pull the globe off and clean 
the globe inside, and make sure everything is OK. 

  7.40) Variable speed ceiling fan on normal circuit

It is usually not possible to use a normal light dimmer to control the fan
as this uses an AC induction motor.  A dimmer can only be used on the built
in light if a separate wire is available to power it.

Doing this will likely result in a nasty hum or buzz at anything other than
full brightness (speed) or off.  This is both annoying and probably not good
for the fan motor as well.  A dimmer works by reducing the power to the
light by controlling when the voltage is applied on each cycle of the AC.  If
it is turned on half way through the cycle half the power is provided, for
example.  However, with cheap lamp dimmers, this results in sharp edges on
the waveform rather as peak voltage is applied suddenly rather than with the
nice smooth sinusoid.  It is these sharp edges causing the coils or other
parts of the fan to vibrate at 120 Hz that you are hearing.

Special speed controls designed for ceiling fans are available - check your
local home center or ceiling fan supplier.

Here is another alternative:

(From: Rick & Andrea Lang (rglang@radix.net)).

Here's a potential solution if you don't mind spending a little more for 
a ceiling fan (If you already have one in that location, perhaps you can put
it in another room).  Ceiling fans with remote control are now available. 
They only require power to the ceiling fan (2 wire) and a remote 
control. With the remote you can dim the lights, slow the fan or both. 
You can then use the existing new wall switch as a power ON/OFF switch 
also. If you choose this route, be careful of interference with garage 
door openers. Usually, the remotes have at least 4 frequency selections 
to help avoid interference with other remote systems. I put one in that 
three of the four frequencies opened the garage door. I lucked out on
the 4th one!

  7.41) Throbbing noise from ceiling fan

This could be due to a mechanical problem - bad bearings or blades out of
balance - or an electrical problem with the speed control.

(From: David Buxton (David.Buxton@tek.com)).

A quickie test.  Get the fan turning at a speed that demonstrates the 
throbbing noise.  Come up with a way to instantly remove power to the 
fan.  If the noise continues for a little bit until the fan has slowed 
down enough, then you know the noise is in the mechanical dynamics, 
perhaps blades out of balance.  If the noise quits instantly with power 
removal, then you need a better speed control better designed for fan 
motor control.

  7.42) Ceiling fan motor speed control and capacitor replacement

(From: Kevin Astir (kferguson@aquilagroup.com)).

Ceiling fans are normally multipole, capacitor-run  types.  They normally
run fairly close to stalled, the blades being big enough that the motor
never gets anywhere near synchronous speed.

Speed control in three speed types is by switching the value of the cap
in series with the quadrature windings. The caps normally have two
sections of 3 and 6 uF,  with a common connection between the two
sections allowing connections of 3, 6, or 9 (3 in parallel with 6) uF

I have seen some caps of slightly different value, but they should be
close, just translate my 3 and 6 to what you actually have in what

The higher the capacitance the higher the stall torque, so the faster
the fan runs against the non-linear (square-law) torque vs. speed
characteristic of the blades. (remember I said it is always pretty
much stalled)

If you miswired the cap, then you may be getting 3 or 6 and 2 (3 in
*series*  with 6 uF which would result in low speeds.  This *is* the
case if any 2 out of 3 speeds seem to be the same. The replacement caps
are usually marked with what terminal is which, but originals often are
not.  I don't know if there is a standard color code, but manufacturers
are under no obligation to adhere to it even if there was.  If you are
totally lost, there are only 6 possible ways to connect the capacitor.
2 of these will give you all 3 speeds (but one in wrong order).  So if
you keep good notes (essential here) then you could try all possibilities
in 20 minutes or so...yes, you're probably working with hands over head,
what you wanted easy too?

OK, here is how to get it in 3 tries max:

Identify the "common"  capacitor lead  (connects to both 3, and 6 uF
sections, hopefully your replacement is marked). It is currently
connected to the wrong place, so swap it with one of the other cap
wires.  If you now have three speeds in the correct order, then your
done.  If you have three speeds in the wrong order, then leave common
wire alone, but swap other two. (correct order is: off-hi-med-lo

If you *didn't* have three different speeds following the first wire
swap, then swap that common wire with the one wire you haven't moved
yet. Now you should have three speeds, now correct the order as
described, if needed.

If you currently have three speeds, but all are too slow, then it is
likely that your fan needed a higher value capacitor. another
explanation might be that the old cap was getting leaky when it
warmed up after start, and letting the fan have extra current, thus
giving extra speed.

In my experience, the three speed types should run from just slow
enough to follow with the eye, to fast, fairly noisy, and making a
fair amount of wobble on the mounting.

Continuously variable speed types put a  fixed 9 or 10 uF cap in
series with the quadrature winding, and regulate voltage to both
windings via lamp-dimmer style triac circuit.

  7.43) Mike's notes on ceiling fan installation

(From: morris@cogent.net (Mike Morris)).

Depending on what wiring you have and what new wiring needs to be installed,
I would install 14/3 cables for all ceiling lights. That way, you will be able
to control ceiling fan and light from two separate switches.

Each time a new light has to be installed in our house, I make sure a 14/3
wire is installed. For three-way switches, I make it two 14/3 wires, even
if I don't install a ceiling fan now. A 14/3 wire is not that much more
expensive, and 10 years down the road, it might be useful.

The local high-end lights-and-fans shops have a handout that recommends
that wherever a ceiling fan is to go have the following wiring:

1. Neutral

2. Ground (if local code requires it, good idea anyway)

3. Switched hot for the lights

4. Switched hot for the fan

5. An extra wire - some brands need 2 hots for the fan, and
   if your brand doesn't need it, an extra conductor doesn't hurt.

Why two switched hots?

* It allows to run the lights and fan separately. 

* You should not use a lamp dimmer as a motor speed control.  While it may
  work to some extent, the motor will likely hum and long term reliability
  and safety are questionable.

Note that this does not preclude using a fan with built-in controls - unused 
wire is just that. And pulling in 5 conductors during construction or 
remodeling costs just a little more that pulling in 2 or 3.

The handout sheet also point out that adding a extra brace to the ceiling 
during any remodeling or new construction sized for a 100 pound dead weight
is a good idea - it can be as simple as a couple of feet of 2x6" lumber and a 
couple of sheet metal fasteners. A wobbling fan can cause fatigue in a light 
duty metal brace rapidly.  The extra cost is minimal, and it can prevent a fan 
from landing in the middle of the bed! 

  7.44) Air cleaners

Simple air cleaners are just a motor driven fan and a foam or other filter
material.  HEPA (High Efficiency Particulate Air) types use higher quality
filters and/or additional filters and sealed plenums to trap particles down to
a specified size (.3 micron).  A clogged (neglected) filter in any air cleaner
is probably the most likely problem to affect these simple devices.  Failure
of the fan to operate can be a result of any of the causes listed above in the
section: "Portable fans and blowers".

Electronic air cleaners include a high voltage low current power supply and
oppositely charged grids in the air flow. A failure of the solid state high
voltage generator can result in the unit blowing air but not removing dust and
particulate matter as it should.  A typical unit might have 7.5 to 10 KV at
100 uA maximum (short circuit current, probably less at full voltage).  Actual
current used is negligible under normal conditions.  This voltage is
significant but the current would be just barely detectable, if at all.

The modules are usually quite simple: a transistor or other type of switching
circuit driving a step-up transformer and possibly a diode-capacitor voltage
multiplier.  See the sections: "Electronic air cleaner high voltage module schematic" and "Auto air purifier schematic" for an example of a typical

Where there is no high voltage from such a device, check the following:

* Make sure power is actually getting to the high voltage portion of the unit.
  Test the wall socket and/or AC adapter or other power supply for proper
  voltage with a multimeter.

* Excessive dirt/dust/muck/moisture or physical damage or a misplaced paper
  clip may be shorting it out or resulting in arcing or corona (a strong aroma
  of ozone would be an indication of this).  With such a small available
  current (only uA) it doesn't take much for contamination to be a problem.
  Thoroughly clean and dry the unit and check for shorts (with a multimeter
  between the HV electrodes and case) and then test it again.  Your problems
  may be gone!

* If this doesn't help and the unit is not fully potted (in which case,
  replacement is the only option), check for shorted or open components,
  especially the power semiconductors.

  7.45) Electronic air cleaner high voltage module schematic

At least I assume this cute little circuit board is for an electronic air
cleaner or something similar (dust precipitator, positive/negative ion
generator, etc.)!  I received the unit (no markings) by mistake in the mail.
However, I did check to make sure it wasn't a bomb before applying power. :-)

This module produces both positive and negative outputs when connected to 115
VAC, 60 Hz line voltage.  Each is about 5 KV at up to around 5 uA.

The AC line powered driver and HV multiplier are shown in the two diagrams,

                   D1                                            T1  o
  H o--------------|>|----+---+--------------------+                +-----o A
                 1N4007   |   |        Sidac     __|__ SCR1     |:|(
                          |   |   R3  D2 100 V   _\_/_ T106B2   |:|(
  AC                  C1  |   +--/\/\---|>|      / |   200 V    |:|(
 Line      Power  .15 uF _|_     1.5K   |<|--+--'  |   4 A    o |:|( 350 ohms
          IL1 LED   250V ---                _|_    |  +-------+ |:|(
        +--|<|---+        |              C2 ---    |  |        )|:|(
        |   R1   |   R2   |        .0047 uF  |     |  | .1 ohm )|:|(
  N o---+--/\/\--+--/\/\--+                  +-----+--+        )|:|(
           470      3.9K  |                                +--+     +--+--o B
           1 W      2 W   |                                |    R4     |

The AC input is rectified by D1 and as it builds up past the threshold of the
sidac (D2, 100 V), SCR1 is triggered dumping a small energy storage capacitor
(C1) through the primary of the HV transformer, T1.  This generates a HV pulse
in the secondary.  In about .5 ms, the current drops low enough such that the
SCR turns off.  As long as the instantaneous input voltage remains above about
100 V, this sequence of events repeats producing a burst of 5 or 6 discharges
per cycle of the 60 Hz AC input separated by approximately 13 ms of dead time.

The LED (IL1) is a power-on indicator. :-)

The transformer was totally potted so I could not easily determine anything
about its construction other than its winding resistances and turns ratio
(about 1:100).

                                            A o
                                     C3       |
          R5     R6      D3   |   D4     D5   |  D6     R7       R8
  HV- o--/\/\---/\/\--+--|>|--+--|>|--+--|>|--+--|>|---/\/\--+--/\/\--o HV+
         10M    10M   |      C4       |                220K  |  10M
                      +------||-------+                      |
       D3-D6: 10 KV, 5 mA            _|_                    _|_
       C3,C4: 200 pF, 10 KV          --- C5                 --- C6
       C5,C6: 200 pF, 5 KV            |                      |
                                 B o--+----------------------+

The secondary side consists of a voltage tripler for the negative output
(HV-) and a simple rectifier for the positive output (HV+).  This asymmetry is
due to the nature of the unidirectional drive to the transformer primary.

From my measurements, this circuit produces a total of around 10 KV between
HV+ and HV-, at up to 5 uA.  The output voltages are roughly equal plus and
minus when referenced to point B.

I assume the module would also operate on DC (say, 110 to 150 V) with the
discharges repeating continuously at about 2 KHz.  Output current capability
would be about 5 times greater but at the same maximum (no load) voltage.
(However, with DC, if the SCR ever got stuck in an 'on' state, it would be
stuck there since there would be no AC zero crossings to force it off.  This
wouldn't be good!)

  7.46) Auto air purifier schematic

Well, maybe :-).  This thing is about the size of a hot-dog and plugs
into the cigarette lighter socket.  It produces a bit of ozone and who knows
what else.  Whether there is any effect on air quality (beneficial or
otherwise) or any other effects is questionable but it does contain a nice
little high voltage circuit.

                                                                   DL1 +-+ |
                                                   o  T1 +-------+-----|o|
  +12 o---+--------+----------+---------------------+ ||(        |     +-+ |
          |        |          |                D 30T )||(        | DL2 +-+
          |        |        -_|_ 4.7uF           #30 )||(        +-----|o| |
          |        |         --- 50V         +------+ ||( 3000T  |     +-+
          |       _|_ C2    + |              |        ||( #44    | DL3 +-+ |
          |       --- 470pF   +--------------|------+ ||(        +-----|o|
          |        |          |              | F 30T )||(        |     +-+ |
        +_|_ C1    |          |       D1     |   #36 )||(        | DL4 +-+
         --- 33uF  +----------|---+---|<|----|------+ ||(        +-----|o| |
        - |  16V   |          |   | 1N4002   |     o     +--+          +-+
          |        /          /   |        |/ C           o |              | 
          |     R1 \       R2 \   +--------|Q1  TIP41       +--------------+
          |     1K /     4.7K /            |\ E             |            Grid
          |        \          \              |              |
          |        |          |              |              |
  GND o---+--------+----------+--------------+--------------+

T1 is constructed on a 1/4" diameter ferrite core.  The D (Drive) and F
(Feedback) windings are wound bifilar style (interleaved) directly on the
core.  The O (Output) winding is wound on a nylon sleeve which slips over
the core and is split into 10 sections with an equal number of turns (100
each) with insulation in between them.

DL1 to DL4 look like neon light bulbs with a single electrode.  They glow like
neon light bulbs when the circuit is powered and seem to capacitively couple
the HV pulses to the grounded grid in such a way to generate ozone.  I don't
know if they are filled with special gas or are just weird neon light bulbs.

  7.47) Bug zappers

You know the type - a purplish light with an occasional (or constant) Zap!
Zap! Zap!  If you listen real closely, you may be able to hear the screams of
the unfortunate insects as well :-).

The high-tech versions consist of a high voltage low current power supply and
fluorescent (usually) lamp selected to attract undesirable flying creatures.
(Boring low-tech devices may just use a fan to direct the insects to a tray of
water from which they are too stupid to be able to excape!)

However, these devices are not selective and will obliterate friendly and
useful bugs as well as unwanted pests.

Here is a typical circuit:

         S1        R1         C1            C2            C1-C4: .5 uF, 400 V
  H o----o/ o--+--/\/\--------||---+--------||---------+  D1-D5: 1N4007
               |  25K        D1    |   D2        D3    |   D4
               |         +---|>|---+---|>|---+---|>|---+---|>|---+
              +-+        |        C3         |        C4         |
 AC Line      |o| FL1    +---+----||----+----+---+----)|----+----+--o + 
              +-+ Lamp   |   |    R3    |        |    R4    |        500 to
               |         |   +---/\/\---+        +---/\/\---+        600 V
               |   R2    |       10M                 10M             to grid
  N o----------+--/\/\---+------------------------------------------o -

This is just a line powered voltage quadrupler.  R1 and R2 provide current
limiting when the strike occurs (and should someone come in contact with the
grid).  The lamp, FL1, includes the fluorescent bulb, ballast, and starter (if
required).  Devices designed for jumbo size bugs (or small rodents) may use
slightly larger capacitors!

(From: Jan Panteltje (pante@pi.net)).

I have one, bought it very cheap: they are only $10 here :)

It comes with a 25 W blue lamp inside, with wires around it.  The lamp did not
last long, so I replaced that with a 7 W electronic fluorescent type, that now
just keeps going and going and going.  The bugs do not care, they just go for
the light.  Then they hit the wires.

Here, we have 230 V, in the lamp is a voltage doubler, with 2, 220 nF
capacitors, 2 silicon diodes, and a 10 K Ohm series resistor in the mains.
The whole thing cannot be touched by humans from outside.  The voltage between
the wires is something like 620 V.  If an insect shorts the wires, the 10K
limits the current until it is destroyed (the insect that is).  The insect
actually explodes, the 600 V cap discharges into it.

  7.48) Electric fences

Yes, I know, this isn't a common small appliance but....

(From: John Harvey (johnharvey@bigpond.com)).

Most DIY fence energizers use an automotive ignition coil and kits (generally
minus coil) are available in Australia and probably elsewhere.

Commercial units operate on the capacitor discharge principle and are fired at
a 1.2 second interval.  Voltage O/P needs to be around 5 to 8 KV (which will
drop under load).  The energy O/P (pulse duration) is determined by the
capacitor and 10 to 20 uF is about right for a small unit (up to 2km or so).
They must use a pulse grade capacitor (which has a high dV/dt) to be reliable.

  7.49) Appliance and light timers

There are two basic types: mechanical and electronic.

* Mechanical timers are simply a synchronous timing motor and gear reducer
  controlling a two prong (usually polarized) outlet.

  The most common problems relate to failure of the timing motor or gear
  train.  With time, the oil and grease used inside the timing motor may
  gum up.  Eventually, it gets so stiff that the motor stops - or more likely -
  doesn't start up after a power failure or the unit has been unplugged for
  a while.

  The cheap plastic gears may also break, chip, or loose teeth.

  Sometimes, disassembly, cleaning, and lubrication, will get the motor
  going - possibly for a long time.  However, replacement parts are rarely
  worth the cost compared to a complete new timer.

* Fully electronic timers use digital clock-type circuitry to control a triac
  or other solid state switching device.

  These may fail in the same way as other electronic controls such as dimmers.
  Most likely problems are that they are either stuck off or stuck on.  Aside
  from testing for bad connections or shorted or open components (with power
  OFF or disconnected!), repair is probably economical.  Assuming it can be
  opened non-destructively at all, check the triac and other parts in its
  vicinity.  The rest of the circuitry is probably in a proprietary chip - but
  these don't fail much.

  Also see the section: "Warnings about using compact fluorescent lamps on electronic timers".

  7.50) Warnings about using compact fluorescent lamps on electronic timers

You may have seen these warnings in the instructions or on the package of
electronic (not mechanical) timers and/or compact fluorescents.

There are two issues:

1. Providing the trickle current to operate the clock circuitry in the timer.

   Where a solid state timer is used to replace a normal switch, there is
   usually no connection to the Neutral so it must derive all its operating
   power from current through the load (though at a very low current level).

   The type of circuitry in a compact fluorescent with an electronic ballast
   (or other equipment with a switching power supply like a TV, some VCRs,
   computer, etc.) may result in this current being too low or erratic.  The
   result will be that the timer doesn't work properly but damage isn't that
   likely (but no guarantees).

   If it is installed with 3 wires (Hot, Neutral, Load), then this should not
   be a problem.

   In addition, interference (e.g., spikes) from the CF ballast may feed back
   into the electronic timer and this may either confuse or actually result
   in failure.

2. Damage to either or both of the devices dues to incompatibility.

   The solid state switching device - usually a triac - in the timer unit
   may be blown by voltage spikes or current surges when the power goes on or
   off into an inductive or capacitive load like an electronic ballast (or
   normal magnetic ballast, for that matter.

In short, read and follow label directions!  Although a given combination may
actually work reliably for years even if it is not supposed to but you should
be able to find a pair for which this shouldn't be a problem.

  7.51) Wall thermostats

These can be divided into several classes depending on:

* Normal or setback (electronic or electromechanical).
* 24 VAC or self powered (thermopile or thermocouple) valve control.
* Heating, airconditioning, or combination.

It is not possible to cover all variations as that would require a
complete text in itself.  However, here is a summary of possible
problems and solutions.

Conventional thermostats usually use a bimetal strip or coil with a
set of exposed contacts or a mercury switch.  In general, these are
quite reliable since the load (a relay) is small and wear due to
electrical arcing is negligible.  On those with exposed contacts, dirt
or a sliver of something can prevent a proper connection so this is
one thing to check if operation is erratic.  The following description
assumes a single use system - heating or cooling - using 24 VAC control
which is not properly controlling the furnace or airconditioner.

1. Locate the switched terminals on the thermostat.  Jumper across them
   to see if the furnace or airconditioner switches on.  If it does, the
   problem is in the thermostat.  If nothing happens, there may be a
   problem in the load or its control circuits.  Cycle the temperature dial
   back and forth a few times to see if the contacts ever activate.  You
   should be able to see the contacts open and close (exposed or mercury)
   as well.

   (CAUTION: on an airconditioner, rapid cycling is bad and may result in
   tripped breakers or overload protectors so ideally, this should be done
   with the compressor breaker off).

2. Check for 24 VAC (most cases) across the switched circuit.  If this
   is not present, locate the control transformer and determine if it
   is working - it is powered and its output is live - you may have the
   main power switch off or it may be on a circuit with a blown fuse or
   tripped breaker.  I have seen cases where the heating system was on
   the same circuit as a sump pump and when this seized up, the fuse blew
   rendering the heating system inoperative.  Needless to say, this is not
   a recommended wiring practice.  The transformer may be bad if there is
   no output but it is powered.  Remove its output connections just to make
   sure there is no short circuit and measure on the transformer again.

3. If 24 VAC is present and jumpering across the terminals does nothing,
   the heater valve or relay or airconditioner relay may be bad or there
   is a problem elsewhere in the system.

4. Where jumpering the terminals turns on the system, the thermostat contacts
   may be malfunctioning due to dirt, corrosion, wear, or a bad connection.
   For a setback unit, the setback mechanism may be defective.  Test and/or
   replace any batteries and double check the programming as well.  On
   those with motor driven timers operating off of AC, this power may be

5. Where jumpering the terminals does not activate the system, check the 
   load.  For a simple heating system, this will be a relay or valve.  Try
   to listen for the click of the relay or valve.  If there is none, its
   coil may be open though in this case there will be no voltage across the
   thermostat contacts but the 24 V transformer will be live.  If you
   can locate the relay or valve itself, check its coil with an ohmmeter.

6. If the previous tests are ok, there may be bad connections in the wiring.

Type of control - most systems use a 24 VAC circuit for control.  However,
some use low voltage self powered circuits that require special compatible
(sometimes called thermopile or thermocouple) thermostats with low resistance
contacts and no electronics directly in series with the control wires.
Erratic or improper control may result from using the wrong type.

Setback thermostats - these may be controlled electromechanically by a
timer mechanism which alters the position of the contacts or selects
an alternate set.  Newer models are fully electronic and anything beyond
obvious bad connections or wiring, or dead batteries is probably not
easily repaired.  However, eliminate external problems first - some of
these may need an additional unswitched 24 VAC or 115 VAC to function
and this might be missing.

Heat anticipators - in order to reduce the temperature swings of the heated
space, there is usually a small heating element built into the thermostat
which provides some more immediate feedback to the sensor than would be
possible simply waiting for the furnace to heat the air or radiators.  If
this coil is defective or its setting is misadjusted, then erratic or much
wider than normal temperature swings are possible.  There will usually be
instructions for properly setting the heat anticipator with the thermostat
or furnace.

Units that control both heating and airconditioning are more complex and
will have additional switches and contacts but operate in a similar manner
and are subject to similar ailments.

  7.52) Electric space heaters

All types have one thing in common - they are nearly 100% efficient which
means that just about every watt of power utilized is turned into heat.
The remainder is used for any built in fans or the wasted light produced
by glowing elements or quart lamps.

However, this does not mean that these are the most economical heating
devices.  Heat pumps based on refrigeration technology can be much less
costly to run since they can have coefficients of performance - the ratio
of heat output to energy input - of 3 or more to 1.  Thus, they are in
effect, 300% or more efficient.  Note that this does not violate any
conservation of energy principles as these simply move heat from one place
to another - the outdoors is being cooled off at the same time.

Space heaters come in 3 common varieties:

* Radiant - heating element with polished reflector.
* Convection - heating element and small fan to circulate heated air.
* Oil filled radiator - heating element heats oil and metal fins.

Problems with space heaters are nearly always related to bad heating elements,
problems with the thermostat, interlock switches, or fan (if any), or bad
connections.  Blown fuses or tripped circuit breakers are very common with
these appliances as they are heavy loads - often the maximum that can safely
be plugged into a 15 A outlet - and thus overloads are practically assured
if **anything** else is used on the same circuit.  Since we rarely keep
track of exactly what outlets are on any given circuit, accidentally using
other devices at the same time are likely since the same circuit may feed
outlets in more than one room - and sometimes some pretty unlikely places.

  7.53) Radiant space heaters

These use a coiled NiChrome, Calrod(tm), or quartz lamp heating element.
There is no fan.  A polished reflector directs the infra red heat energy
out into the room.  Radiant space heaters are good for spot heating of
people or things.  They do not heat the air except by convection from the
heated surfaces.

Of course, first check that the outlet is live.

As with other heating appliances, the most likely problems are with burned
out heating elements; defective on/off switches, thermostats, or safety
interlock or tip-over switches, bad cord or plug, or bad wiring connections.
Your continuity checker or ohmmeter will quickly be able to identify which
of these are the problem.

Warning: do not be tempted to bypass any interlock or tip-over switches
should they prove defective.  They serve a very important fire and personal
safety function.  Never, ever cover the heater in any way as a serious fire
hazard will result.

  7.54) Convection space heaters

A small fan blows air over or through a heating element.  This may be a
NiChrome coil, Calrod(tm) element, or ceramic thermistor.  This type
is probably the most popular since it can quickly heat a small area.
The ceramic variety are considered safer than the others (of this type)
since they are supposed to operate at a lower surface temperature.

In addition to the problems covered in the section above: "Radiant space heaters", the fan can also become sluggish or seize up due to
gummed up lubrication (as well as other fan-motor problems).  Since
it is running in a high temperature environment, disassembly, cleaning,
and lubrication may be needed periodically despite what the manufacturer
may say about permanently lubricated parts.

  7.55) Oil filled electric radiators

These are also considered convection heaters but they do not have any fan.

The typical unit consists of a pair of heating elements providing 600, 900,
or 1500 Watts depending on which are switched on.  A simple bimetal
adjustable thermostat is used for temperature control.  The heating
elements are fully submerged and sealed inside an oil filled metal finned
replica of an old style radiator.  The whole affair is mounted on wheels
as it is quite heavy.

Common problems with these have been the pair of power switches which tend
to fail resulting in no or erratic operation.  Note: if your heater is a
Delongi, there has been a free (well $5 S&H) upgrade to replace the failure
prone power switches and thermostat on some common models.

The heating elements are replaceable (as a set).  Since they are immersed in
the oil, you MUST have the radiator on its end with the terminals straight up
while changing them or else there will be a mess.  Replacement will be worth
the cost and effort only if you require the high settings as it is unlikely
for both elements to fail.  If testing reveals an open element, you will just
not have the heat ranges that use it.  If an element shorts to the case, it
must be disconnected to prevent a shock hazard though the other one can still
be safely used.  Parts should be available.

  7.56) So, what about the Pelonus Disk furnace?

(From: Kirk Kerekes (kkereke@iamerica.net)).

It is a portable electric heater, using high-power thermisters as the heating
elements. This technology was originally developed by TDK a few decades ago.
The premise is that the power thermisters will automatically control the
heating element temperature (the thermister), so that if the air flow is
blocked, the heater won't cook. The manufacturers make efficiency claims, but
these seem to be bogus.  (All space heaters are nearly 100% efficient.  See
the section: "Electric space heaters" --- sam.)

I have a bathroom version of this device, and it works.

  7.57) Electric pencil sharpeners

AC powered pencil sharpeners consist of a small shaded pole induction
motor, pencil sense switch, and some gears and cutter wheels.  Aside
from pencil shavings crudding up the works - which can be cleaned - the
most common failure is of the cheap plastic gears.  These can be easily
be replaced if you can get them - the original manufacturer is likely the
only source.  The switch contacts may become dirty or level/bar may become
misaligned or worn.  Some clever repositioning or the addition of a shim
may help in these cases.

Battery operated pencil sharpeners use a small DC motor for power.  These
tend to be whimpier than their AC counterparts but all other comments
apply.  Always try a fresh set of batteries first.

  7.58) Blenders

A blender really is just a high speed motor mounted inside a base.  Units
with 324 speeds accomplish (this more or less useless marketing gimmick)
through a combination of diodes, resistors, and multiple windings on the
motor.  Without addressing the ultimate utility of thousands of speeds,
problems with these units are more likely to be in the motor itself - open
or shorted windings, or bad bearings.  However, the selector switches and
electrical parts can fail as well.

The motors are typically of the series wound universal type.  These have
carbon brushes which are prone to wear.  However, given the relatively short
total usage of a blender, this is not usually a problem.

Disconnecting (and labeling!) connections one at a time may permit the
source of a problem to be localized.  Diodes can be tested with a multimeter
(they should read open in one and only one direction) and resistors checked
as well.  Shorts in a motor with multiple taps on its windings may be
difficult to identify or locate.  Shorted windings can result in overheating,
incorrect speeds, or even a blender that runs with the power switch supposedly
in the off position as the wiring is sometimes sort of strange!

Bad bearings will result in any number of mechanical problems including
excessive or spine tingling noise, vibration, a seized rotor or very sluggish
rotation.  Sometimes, disassembly, cleaning, and oiling will be effective
but since these rotate at high speed, don't count on it.  Unfortunately,
cheap bronze bushings are often used instead of ball bearings.  However,
substituting a set from another similar unit might work since it is usually
the bronze bushing and not the motor shaft that fails.

The most sophisticated units will have a variable speed control - similar
to a light dimmer.  If this goes bad - the blender always runs at full
speed - then the active element (triac) has probably blown.  Replacement
is possible and the part types should be readily available.

  7.59) Drip coffee makers

A drip coffee maker consists of several components:

1. A heating element - combined or separate Calrod(tm, usually) types
   for operating the drip pump and then keeping the coffee warm.

2. Thermal protector - to prevent excess temperatures.

3. Some kind of water interlock - prevents dripping when separate reservoir
   is used.

4. Timer or controller.  The simplest are mechanical while programmable
   units with clocks and electronic timers are also available.

Many problems are be mechanical - clogged water passages or interlock.
Extended use with hard/high mineral content water can also result in reduced
heating effectiveness and/or increased heating times.  It may be possible to
flush the unit a couple of times with viniger.

If there is no heating, check the element and thermal protector with an
ohmmeter.  If the element is open, it is probably time for a new coffee maker.
The thermal protectors can be replaced but the underlying cause may be a
defective, shorted overheating element so it may not be worth the trouble.
Timers can develop bad contacts and bad connections are possible on electronic
controller circuit board wiring.

  7.60) Drop coffee maker repair

(From: Niels Henriksen (ap294@FreeNet.Carleton.CA)).

I wish I had thought of this sooner rather than throwing out the first 
coffee maker and I had planned to throw this one out.  For some reason I 
thought I would just look inside to see what was up.

Where I live the water is hard (well) and there is constant scaling and 
buildup of calcium.  We heard that all you have to do is to run a 
mixture of vinegar through the coffee maker to rejuvenate.

A friend and the 2 of ours all started to leak very badly when the 
vinegar/water mixture when through.  I though that the internal plumbing 
had corroded through the metal parts and the vinegar dissolved the 
calcium that was protecting the holes and therefore unrepairable. Who 
knows where these ideas come from.

Now for the technical solution.

The element that is used to boil the water and uses the bubbles to bring 
hot water to top of coffee maker is the same element that is used to 
keep the pot warm.

There is a metal tube attached to the metal warming element and this 
unit has a heating element embedded. There are 2 rubber hoses attached. 
One brings cold water to heater and the other brings boiling water to 
top. The cold water tube has a check valve that prevents the bubbling 
water from going to cold water reservoir.

When vinegar is added the calcium scales start to dissolve and in 3 of 3 
so far, this blocked the metal tube.  The water starts to boil and since 
the cold water inlet has a check valve the water pressure can only 
buildup to where the rubber tube is blown off the metal pipe.
No damage to parts.

To fix:

1. Take bottom off to gain access to heater area.

2. Remove rubber tubes which are connected with spring clamps.

3. Run rubber tubes through your fingers to loosen scale buildup and flush out

4. push a thin copper wire or other bendable wire through heating tube.  This
   is to unblock and loosen some scale.

5. Pour straight vinegar into metal tube to dissolve calcium and use wire to

6. Repeat several times till clean.

7. Re-attach all parts and use.

The solution is to start a regular process of using vinegar BEFORE the
calcium has buildup to the point where when loosened it will block the tube.

  7.61) Coffee percolators

While largely replaced by the drip coffee maker, these are still available,
particularly in large sizes.  The components are similar to those in a
drip coffee maker - element, thermal protector, possibly a thermostat
as well.  The element and bottom of the water/coffee container are likely
one piece to provide the best thermal conduction for the 'pump' in the
middle.  Even if the element is removable, it may not be worth the cost
of replacement except for a large expensive unit.

  7.62) Electric kettles

These consist of a heating element, thermal protector, and possibly a
thermostat and/or timer.  See comments for coffee makers.

  7.63) Electric (motor driven) clocks

While line operated clocks have mostly been superseded by electronic
(LED or LCD) clocks on nearly every kitchen appliance, many of these
are still in operation on older clock radios and ranges.

AC operated clocks depend on the AC line frequency (60 Hz or 50 Hz
depending on where you live) for time keeping.  The accuracy of a
line operated clock is better than almost any quartz clock since 
the long term precision of the power line frequency is a very carefully
controlled parameter and ultimately based on an atomic clock time standard.

Therefore, most problems are related to a clock motor that does not run or
will not start up following a power outage.  Once running, these rarely fail.

The most common problems are either gummed up oil or grease inside the
motor and gear train, broken gears, or broken parts of the clock mechanism
itself.  See the sections on "Synchronous timing motors" for repair info.

Battery operated quartz clocks usually operate on a 1.5 V Alkaline cell
(do not replace with NiCds as they do not have a long absolute life
between charges even if the current drain is small as it is with a clock).

First, test the battery.  Use a multimeter - usually anything greater than
1 V or so will power the clock though if it is closer to 1 V than 1.5 V,
the battery is near the end of its life.  The clock may run slow or fast
or erratically on a low battery.

With a good battery, failure to run properly is usually mechanical - one
of the hands is hitting against the glass front or something like that.
Don't forget to check any on/off switch - these are not expected but are
often present presumably to permit you to start the clock at precisely the
right time.  I had one case where the fine wire to the solenoid that
operates the once per second clock mechanism broke and had to be resoldered
but this is exceedingly rare.

If the clock consistently runs slow or fast with a known good battery,
there is usually a trimmer capacitor that can be adjusted with a fine
jeweler's straight blade screwdriver.  Without test equipment the best
you can do is trial and error - mark its original position and turn it
just a hair in one direction.  Wait a day or week and see if further
adjustment is needed (right, like you also won the lottery!) and fine
tune it.

If the hands should fall off (what a thought!), they can usually be pressed
back in place.  Then, the only trick is to line up the alarm hand with the
others so that the alarm will go off at the correct time.  This can usually
be done easily by turning the hour hand counterclockwise using the setting
knob in the rear until it is not possible to turn it further.  At this point,
it is lined up with the alarm hand.  Install all hands at the 12:00 position
and you should be more or less all set.

  7.64) Rotisseries

The mechanism consists of a shaded pole induction motor and gear train.
Clean and lubricate the gears.  See the section: "Shaded pole induction motors" for motor problems.

  7.65) Electric can openers and knife sharpeners

There consist of a shaded pole induction motor, gear train. and power
switch.  Likely problems relate to broken gear teeth, dirty or worn
power switch, dull cutting wheel, and broken parts.  Lubrication may
be needed if operation is sluggish.  Parts that come in contact with
the cans and lids collect a lot of food grime and should be cleaned

  7.66) Electric carving knives

A small motor operates a pair of reciprocating mounts for the blades.

AC powered carving knives include a momentary power switch, small motor
(probably universal type), and some gearing.  Congealed food goo as well
as normal lubrication problems are common.  The power switch is often
cheaply made and prone to failure as well.  The cord may be abused (hopefully
not cut or damaged by careless use of the knife!) and result in an intermittent
connection at one end or the other.  For motor problems, see the appropriate
sections on universal motors.

For battery powered knives, bad NiCds cells are a very likely possibility due
to the occasional use of this type of appliance.

See the section: "Small permanent magnet DC motors" and the chapter:
"Batteries" for information on repair.

  7.67) Electric scissors

Similar to electric carving knives except for the linkage to the blades.
All other comments apply.

  7.68) Portable and stationary food mixers

These consist of a universal motor which usually features a continuously
variable speed control or a selection of 3 to 5 speeds, a gearbox to transfer
power to the counter-rotating beaters, and a power switch (which may be
part of the speed control).

Sluggish operation may be due to cookie dough embedded in the gearing.  Fine
particles of flour often find their way into the gears - clean and lubricate.
There may be a specific relationship that needs to be maintained between
the two main beater gears - don't mess it up if you need to disassemble and
remove these gears or else the beaters may not lock in without hitting

The speed control may be a (1) selector switch, (2) mechanical control
on the motor itself, or (3) totally electronic.  Parts may be replaceable
although, for portables at least, a new mixer may make more sense.

For sluggish operation (non-mechanical), sparking, burnt smells, etc.,
see the section: "Problems with universal motors".

  7.69) Food processors

A powerful universal motor is coupled to interchangeable cutters of various
types.  In most respects, food processors are similar to any other universal
motor driven appliance with one exception: There will be a safety interlock
switch to prevent operation unless the cover is on properly and secured.  This
switch may go bad or its mechanical position adjustment may shift over time
resulting in difficulty in engaging power - or a totally dead unit.

As usual, cord and plug problems, bad bearings, burnt motor windings,
and broken parts are all possibilities.

  7.70) Steam and dry irons

Most modern irons (does anyone really use these anymore?) can be used
dry or with steam.

An iron consists of a sole plate with an integrated set of heating coils.

Steam irons will have a series of holes drilled in this plate along with
a steam chamber where a small amount of water is boiled to create steam.
A steam iron can be used dry by simply not filling its reservoir with water.
Those with a spray or 'shot of steam' feature provide a bypass to allow
hot water or steam to be applied directly to the article being ironed.

Over time, especially with hard water, mineral buildups will occur in the
various passages.  If these become thick enough, problems may develop.
In addition, mineral particles can flake off and be deposited on the

A thermostat with a heat adjustment usually at the top front of the
handle regulates the heating element.  This is usually a simple bimetal
type but access to the mechanism is often difficult.

Where an iron refuses to heat, check the cord, test the heating element
for continuity with your ohmmeter, and verify that the thermostat is

An iron that heats but where the steam or spray features are missing,
weak, or erratic, probably has clogged passages.  There are products
available to clear these.

Newer irons have electronic timeout controllers to shut the iron off
automatically if not used for certain amount of time as a safety feature.
Failure of these is not likely and beyond the scope of this manual in
any case.

When reassembling an iron, take particular care to avoid pinched or shorted
wires as the case is metal and there is water involved - thus a potential
shock hazard.

  7.71) Toasters

In addition to a fine heating element, there is a controller to determine
the length of time that the bread (or whatever) is heated.  A solenoid
or bimetal trip mechanism is used to pop the bread up (but hopefully not
totally out) of the toaster then it is 'done' and turn off the heating
element at the same time.

Since most of these are so inexpensive, anything more serious than a
broken wire or plug is probably not worth repairing.  The heating
element may develop a broken spot - particularly if something like a
fork is carelessly used to fish out an English muffin, for example.
(At least unplug it if you try this stunt - the parts may be electrically
live, your fork is metal, you are touching it!).  They may just go bad
on their own as well.

Being a high current appliance, the switch contacts take a beating
and may deteriorate or melt down.  The constant heat may weaken various
springs in either the switch contact or pop-up mechanism as well.
Sometimes, some careful 'adjustment' will help.

Controllers may be thermal, timer based, or totally electronic.  Except
for obvious problems like a bent bimetal element, repair is probably not
worth it other then as a challenge.

  7.72) Automatic toaster will not drop bread

If it really is old, then your problem is almost certainly mechanical -
a spring sprung or gummed up burnt raisin bread.  You will have to do
a little investigative research meaning: take the thing apart!  Try to
determine what the bread does to cause the support to drop down. It is
possible that putting the bread in is supposed to trip a microswitch which
activates a solenoid, and the switch or solenoid is now defective - bad
contacts or broken wires, bad coil in the solenoid, or grime.

The following applies directly to several Sunbeam models (and no doubt
to many others as well).

(From: John Riley (jriley@calweb.com)).

I will assume that the  toaster is either a model ATW or possibly an 
older model 20 or the like.

When you drop the bread in the toaster it trips a lever that is attached 
to the bread rack.  This lever pushes in on the contacts inside of the 
thermostat (color control switch) which actually turns the toaster on.
In "most cases" adjusting the screw on the bottom of the toaster will do 
the trick.  The proper adjustment is to adjust the carriage tension so 
that the bread rack in the side where it marked for a single slice of 
bread comes just to the uppermost limit of its travel.  Any more is 

If you have adjusted it as mentioned above and it still won't go down, 
there is one more thing you can try.  Take the toaster a sort of BUMP it 
down onto the table rather firmly.  Sometimes a piece of crumb will get 
in between the thermostat contacts.  A couple of good "bumps" on the 
table will usually dislodge the particle.

If all of the above doesn't work, and you know the cord isn't bad, them 
you may very well have a thermostat that has gone south.  They are still 
available for replacement on most models.  Suggest you check with your 
local SUNBEAM AUTHORIZED SERVICE for price and availability.

  7.73) Toaster oven (broilers)

I really liked the old original style GE toaster oven.  It was very versatile
and convenient for baking and toasting.  The newer types seem to have lost
some of these qualities.  The pop open door and oven tray have apparently
not been retained in any modern models that I am aware of.

Modern toaster oven (broilers) use Calrod style elements - usually two
above and two below the food rack.  Depending on mode, either just the
top (top brown/broil), just the bottom (oven), or both sets (toast) will
be energized.  Each pair may be wired in series meaning that a failure
of one will result in both of the pair being dead.  Very old units may
use a coiled NiChrome element inside a quartz tube.

Thermostats are usually of the bimetal strip variety with an adjustment
knob.  A cam or two on the shaft may also control main power and select
the broil function in the extreme clockwise position.

There may be a mode switch (bake-off-broil) which may develop bad contacts
or may fuse into one position if it overheats.  These are often standard
types and easily replaceable.  Just label where each wire goes on the
switch before removing it to take to an appliance repair parts store.

Newer models may use an electronic timer for the toast function at least.
I assume it is not much more than something like an IC timer (555) operating
the trip solenoid.  However, I have not had to deal with a broken one as

Testing is relatively straightforward.  Check the heating elements, thermostat,
mode switch,, cord, and plug.  While replacements for heating elements and
thermostats are often available, removing the old one and wiring the new one
may not be straightforward - rivets may be used for fastening and welds
for the wire connections.  You will have to drill the rivets with an electric
drill and replace them with nuts, bolts, and lockwashers.  Crimp splices
or nuts and bolts can be used for the wiring.  Take extra care in reassembly
to avoid any bare wires touching the metal cabinet or other parts as well as
insulation being cut by sharp sheetmetal parts.  The high temperature fiberglas
or asbestos insulation is not very robust.  In the end, it may not be
worth it with full featured toaster oven/broilers going for $20-30 on sale.

  7.74) Convection oven noise

Unlike a regular (non-microwave) oven, convection ovens are not totally
silent.  There is a small fan used to circulate the hot air (thus the
name: convection oven).  Depending on the oven's design and age, these
fans may be anywhere from nearly silent to objectionably noisy.

If you notice an increase in motor noise (whining or squealing, grinding,
knocking) then the motor and fan should be inspected and parts replaced
if necessary.  Sudden failure is unlikely but if it were to happen - seized
bearings, for example - an overtemperature thermal protector should shut
down the heating element or entire oven.  Some of these may not be self
resetting (thermal fuse).

  7.75) Hot plates, waffle irons, broilers, deep friers, rice and slow cookers, woks

These are all just a single or dual heating element, thermal protector
(not all will have one), and an adjustable (usually) thermostat.  As usual,
check the cord and plug first, and then each of the other parts with an

Where a NiChrome coil type heating element is used, a break will be obvious.
If it is very near one end, then removing the short section and connecting the
remainder directly to the terminal will probably be fine.  See the section:
"Repair of broken heating elements".

For appliances like waffle irons, burger makers, and similar types with
two hinged parts, a broken wire in or at the hinge is very common.

Note that since these operate at high temperatures, special fiberglass (it
used to be asbestos) insulated wiring is used.  Replace with similar types.
Take extra care in reassembly to avoid shorted wires and minimize the handling
and movement of the asbestos or fiberglas insulated high temperature wiring.

  7.76) Popcorn poppers (oil type)

An Oil popper is basically an electric frying pan with a built-in stirrer and
cover.  The internal parts are accessed from the bottom: Heating coil,
thermostat and thermal protector, and small gear-motor similar to that used
in a clock or timer.  Take care to note the orientation of the motor when
removing and to not damage any seals (you don't want oil seeping down under!).

As always, check for bad connections if the popper is dead or operation is

Problems with heating can arise in the heating element, thermostat, and
thermal protector.

If the stirrer doesn't turn, a gummed up motor or stirrer shaft (since these
are only used occasionally) may be the problem.  See the chapter: "Motors 101".

  7.77) Popcorn poppers (air type)

Air poppers combine a heating element and blower to heat corn kernels without
the need for any unhealthy oil.  Of course, you probably then drown the popcorn
in butter and salt, huh?  Admit it! :-).

As always, check for bad connections if the popper is dead or operation is

Problems with heating can arise in the heating element, thermostat, and
thermal protector.

The motor is probably a small PM DC type and there will then be a set of
diodes or a bridge rectifier to turn the AC into DC.  Check these and for
bad bearings, gummed up lubrication, or other mechanical problems if the
motor does not work or is sluggish.  See the chapter: "Motors 101".

  7.78) Sewing machines

Moth mechanical and electrical problems are possible.  (Note: we are not
going to deal with fancy computerized equipment as this is probably better
left to a professional except for the more obvious problems like a bad
cord or plug.)

I have a 1903 Singer foot-pumped sewing machine which we have since electrified
and still runs fine.  A couple of drops of sewing machine or electric motor
oil every so often is all that is needed.  They were really built well back

Although the appearance of the internal mechanism may appear intimidating
at first, there really is not that much to it - a large pulley drives a
shaft that (probably) runs the length of the machine.  A few gears and
cams operate the above (needle and thread) and below (feet and bobbin)
deck mechanisms.  Under normal conditions, these should be pretty robust.
(Getting the adjustments right may be another story - refer to your users
manual).  Sometimes if neglected, the oil may seriously gum up and require
the sparing use of a degreaser to loosen it up and remove before relubing.

If the motor spins but does not turn the main large pulley, the belt is
likely loose or worn.  The motor will generally be mounted on a bracket
which will permit adjustment of the belt tension.  The belt should be tight
but some deflection should still occur if you press it gently in the middle.

If the motor hums but nothing turns, confirm that the belt is not too tight
and/or that the main mechanisms isn't seized or overly stiff - if so, it
will need to be cleaned and lubrication (possibly requiring partial

The electric motor is normally a small universal type on a variable speed
foot pedal (see the section: "Wiring a sewing machine speed control").

If the motor does not work at all, bypass the foot pedal control to confirm
that it is a motor problem (it is often possibly to just plug the motor
directly into the AC outlet).  Confirm that its shaft spins freely.  All
normal motor problems apply - bad wiring, worn brushes, open or shorted
windings, dirty commutator.  See the section: "Problems with universal motors".

  7.79) Wiring a sewing machine speed control

This assumes a basic sewing machine (nothing computer controlled) with
a normal universal series wound motor (115 VAC).

The common foot pedals are simply wirewound rheostats (variable resistors)
which have an 'off' position when the pedal is released.  They are simply
wired in series with the universal motor of the sewing machine (but not
the light) and can be left plugged in all the time (though my general
recommendation as with other appliances is to unplug when not in use.

While not as effective as a thyristor type speed controller, these simple
foot pedals are perfectly adequate for a sewing machine.  There are also
fancier speed controls and using a standard light dimmer might work in some
cases.  However, there are two problems that may prevent this: the sewing
machine motor is a very light load and it is a motor, which is not the same
as a light bulb - it has inductance.  The dimmer may not work, may get stuck
at full speed, or may burn out.

  7.80) Shavers

A variety of types of drive mechanisms are used in electric shavers:

1. Vibrator (AC only) - these (used by Remington among others) consist of
   a moving armature in proximity to the pole pieces of an AC electromagnet.
   The mass and spring are designed so that at the power line frequency, the
   armature vibrates quite strongly and is linked to a set of blades that
   move back and forth beneath the grille.

   If dead, check for continuity of the plug, cord, switch, and coil.  IF
   sluggish, clean thoroughly - hair dust is not a good lubricant.  Sliding
   parts probably do not require lubrication but a drop of light oil should
   be used on any rotating bearing points.

   Note that since a resonance is involved, these types of shavers may not
   work well or at all on foreign power - 50 Hz instead of 60 Hz or vice
   versa - even if the voltage is compatible.

2. Universal motor (AC or DC) - very small versions of the common universal
   motors found in other appliances.  A gear train and linkage convert the
   rotary motion to reciprocating motion for shavers with straight blades or
   to multiple rotary motion for rotary blade shavers.  These may suffer
   from all of the afflictions of universal motors; bad cords, wires, and
   switches; and gummed up, clogged, or worn mechanical parts.  Also see
   the sections on the appropriate type of motor.  Take care when probing
   or disassembling these motors - the wire is very fine any may be easily
   damaged - I ruined an armature of a motor of this type by poking where
   I should not have when it was running - ripped all the fine wires from
   the commutator right off.

3. DC PM motor - often used in rechargeable shavers running of 2 or 3 NiCd
   cells.  These may suffer from battery problems as well as motor and
   mechanical problems.  One common type is the Norelco (and clone) rotary
   shaver.  See the chapters on Batteries and AC Adapters as well as the
   sections on "Small permanent magnet DC motors".

   A shaver that runs sluggishly may have a dead NiCd cell - put it on
   charge for the recommended time and then test each cell - you should
   measure at least 1.2 V.  If a NiCd cell reads 0, it is shorted and
   should be replaced (though the usual recommendation is to replace all
   cells at the same time to avoid problems in the future).

   Note that in terms of rechargeable battery life, shavers are just about
   optimal as the battery is used until it is nearly drained and then 
   immediately put on charge.  The theoretical 500 to 1000 cycle NiCd life
   is usually achieved in shaver applications.

  7.81) Electric toothbrushes

These are basically similar to any other small battery operated appliance or
tool such as a screwdriver or drill.  The permanent magnet motor runs off of
rechargeable NiCd batteries and cause the bristles or whatever to oscillate,
rotate, or vibrate.  Interchangeable 'brush' units allow each member of the
family to have their own.

Problems can occur in the following areas:

* Motor, battery pack, connections, on/off switch - as with any other similar

* Power train - gummed up lubrication, broken, or other mechanical problems.

* Charging station or circuitry - the fault may be with the base unit or
  circuitry associated with the battery pack.  See the section: "Braun electric toothbrush repair", below.

Since these must operate in a less than ideal environment (humid or actual
waterlogged!), contamination and corrosion is quite possible if the case is
not totally sealed.  Some of the switched may be of the magnetic reed type so
that there don't need to be any actual breaks in the exterior plastic housing.

Of course, getting inside may prove quite a challenge:

(From: Jeff & Sandy Hutchinson (sandy2@flatoday.infi.net)).

It's darned near impossible to replace the batteries on the Interplak
toothbrush without destroying the recharging circuit.  The base of the hand
unit has a little pickup coil in it, and when you unscrew the cap to get at
the batteries, you break the connections to the pickup coil.  Best to do an
exchange with the factory.

  7.82) Braun electric toothbrush repair

(From: David DiGiacomo (dd@Adobe.com)).

This Braun electric toothbrush (original model) would turn itself on and keep
running until its batteries were discharged.

The toothbrush can be disassembled by pulling the base off with slip joint
pliers (do not pull too hard because there is only about 1" of slack in
the charging coil wires).  With the base off, the mechanism slides out of
the case.

There is a simple charging circuit, charging LED, 2 NiCd cells, and a reed
switch driving the base of an NPN transistor.  The transistor collector
drives the motor.

I charged the battery, but the problem of the motor running with the reed
switch open didn't recur until I held my finger on the transistor for
about 10 seconds seconds.  Grounding the transistor base turned it off
again, and I could repeat this cycle.  Since there wasn't anything else to
go wrong I decided to replace the transistor.  I couldn't read the
marking, but it's in a SOT89 package and the motor current is 400-700 mA so
it must be something like a BC868.  However, I didn't have any surface
mount or TO92 transistors that could handle the current, so I used a
2SD882 (small power tab package), which I was able to squeeze into some
extra space in the center of the charging coil.

  7.83) Hand massagers

These are simply motors with an off-axis (eccentric) weight or electromagnetic
vibrators.  If the unit appears dead, check the plug, cord, on/off switch,
internal wiring, and motor for continuity.  Confirm that the mechanical parts
turn or move freely.

Some have built in infra-red heat which may just be a set of small light
bulbs run at low voltage to provide mostly heat and little light (a filter
may screen out most of the light as well).  Obviously, individual light
bulbs can go bad - if they are wired in series, this will render all of
them inert.

At least one brand - Conair - has had problems with bad bearings.  Actually,
poorly designed sleeve bearings which fail due to the eccentric load.  If you
have one of these and it becomes noisy and/or fails, Conair will repair
(actually replace) it for $5 if you complain in writing and send it back to
them.  They would like a sales receipt but this apparently is not essential.

  7.84) Hair dryers and blow dryers

A heating element - usually of the NiChrome coil variety - is combined with
a multispeed centrifugal blower.

First determine if the problem is with the heat, air, or both.

For heat problems, check the element for breaks, the thermal protector
or overtemperature thermostat (usually mounted in the air discharge), the
connections to the selector switch, and associated wiring.

For air problems where the element glows but the fan does not run, check the
fan motor/bearings, connections to selector switch, and associated wiring.
Confirm that the blower wheel turns freely and is firmly attached to the
motor shaft.  Check for anything that may be blocking free rotation if the
blower wheel does not turn freely.  The motor may be of the induction,
universal, or PM DC type.  For the last of these, a diode will be present
to convert the AC to DC and this might have failed.  See the appropriate
section for problems with the type of motor you have.

  7.85) Curling irons

These are just a sealed heating element, switch, and thermal protector
(probably).  Check for bad connections or a bad cord or plug if there is
not heat.  A failed thermal protector may mean other problems.  While
these are heating appliances, the power is small so failures due to
high current usually do not occur.

  7.86) VCR cassette rewinders

Cassette rewinders typically consist of a low voltage motor powered from
a built in transformer or wall adapter, a belt, a couple of reels, and some
means of stopping the motor and popping the lid when the tape is fully

Note that some designs are very hard on cassettes - yanking at the tape
since only increased tension is used to detect when the tape is at the end.
These may eventually stretch the tape or rip it from the reel.  I don't
really care much for the use of tape rewinders as normal use of rewind and
fast forward is not a major cause of VCR problems.  Sluggish or aborted
REW and FF may simply indicate an impending failure of the idler tire or
idler clutch which should be addressed before the VCR gets really hungry
and eats your most valuable and irreplaceable tape.

Problems with tape rewinders are usually related to a broken or stretched
belt or other broken parts.  These units are built about as cheaply as
possible so failures should not be at all surprising.  The drive motor can
suffer from any of the afflictions of similar inexpensive permanent magnet
motors found in consumer electronic equipment.  See the section: "Small permanent magnet DC motors".  A broken belt is very common since increased
belt (and tape) tension is used to switch the unit off (hopefully).  Parts can
pop off of their mountings.  Flimsy plastic parts can break.

Opening the case is usually the biggest challenge - screws or snaps may
be used.  Test the motor and its power supply, inspect for broken or
dislocated parts, test the power switch, check and replace the belt if
needed.  That is about it.

  7.87) Vacuum cleaners, electric brooms. and line powered hand vacs

Despite all the hype surrounding vacuum cleaner sales, there isn't much
difference in the basic principles of operation between a $50 and $1,500
model - and the cheaper one may actually work better.

A vacuum cleaner consists of:

1. A cordset - broken wires or damaged plugs are probably the number one
   problem with vacuums as they tend to be dragged around by their tails!
   Therefore, in the case of an apparently dead machine, check this first -
   even just squeezing and bending the wire may produce an instant of
   operation - enough to verify the cause of the problem.

2. A power switch - this may be a simple on/off toggle which can be tested
   with a continuity checker or ohmmeter.  However, fancy machines with
   powered attachments may have interlocks or switches on the attachments
   that can also fail.  Where multiple attachment options are present, do
   your initial troubleshooting with the minimal set as this will eliminate
   potential sources of additional interlock or switch complications.  With
   'microprocessor' or 'computer' controlled vacuum cleaners, the most likely
   problems are not the electronics.

3. A high speed universal motor attached to a centrifugal blower wheel.
   As with any universal motor, a variety of problems are possible: dirt
   (especially with a vacuum cleaner!), lubrication, brushes (carbon),
   open or shorted windings, or bad connections.  See the section: "Problems with universal motors".

4. A belt driven carpet brush (uprights).  The most common mechanical problem
   with these is a broken rubber belt.  (One person who shall remain nameless,
   mistook the end of the broken belt for the tail of a mouse and promptly
   went into hysterics!).  Replacements for these belts are readily available.

5. Power nozzles and other powered attachments.  Some of these are an attempt
   to give canister type vacuum cleaners the power of an upright with its
   directly powered carpet brush.  Generally, these include a much smaller
   motor dedicated to rotating a brush.  Electrical connections are either
   made automatically when the attachment is inserted or on a separate
   cable.  Bad connections, broken belt, or a bad motor are always

6. A bag to collect dirt.  Vacuum cleaners usually do a poor job of dust
   control despite what the vacuum cleaner companies would have you believe.
   Claims with respect to allergies and other medical conditions are generally
   without any merit unless the machine is specifically designed (and probably
   very expensive) with these conditions in mind.  If the vacuum runs but with
   poor suction, first try replacing the bag.

  7.88) Vacuum cleaner mechanical problems

1. Poor suction - check the dirt bag and replace if more than half full.
   Check for obstructions - wads of dirt, carpet fibers, newspapers, paper
   towels, etc.

2. Poor pickup on floors - broken or worn carpet brush belt.  There should
   be some resistance when turning the carpet brush by hand as you are also
   rotating the main motor shaft.  If there is none, the belt has broken
   and fallen off.  Replacements are readily available.  Take the old one
   and the model number of the vacuum to the store with you as many models
   use somewhat similar but not identical belts and they are generally not
   interchangeable.  To replace the belt on most uprights only requires the
   popping of a couple of retainers and then removing one end of the carpet
   brush to slip the new belt on.

3. Vacuum blows instead of sucks - first confirm that the hose is connected
   to the proper port - some vacuums have easily confused suction and blow
   connections.  Next, check for internal obstructions such as wads of dirt,
   balls of newspaper, or other items that may have been sucked into the
   machine.  Note that it is very unlikely - bordering on the impossible -
   for the motor to have failed in such a way as to be turning in the wrong
   direction (as you might suspect).  Furthermore, even if it did, due to
   the design of the centrifugal blower, it would still suck and not blow.

4. Broken parts - replacements are available for most popular brands from
   appliance repair parts distributors and vacuum/sewing machine repair

  7.89) Vacuum cleaner electrical problems

1. Bad cord or plug - number one electrical problem due to the abuse that
   these endure.  Vacuum cleaners are often dragged around and even up and
   down stairs by their tails.  Not surprisingly, the wires inside eventually
   break.  Test with a continuity checker or ohmmeter.  Squeezing or bending
   the cord at the plug or vacuum end may permit a momentary spurt of
   operation (do this with it plugged in and turned on) to confirm this

2. Bad power switch - unplug the vacuum and test with a continuity checker
   or ohmmeter.  If jiggling the switch results in erratic operation, a new
   one will be required as well.

3. Bad interlocks or sensors - some high tech vacuum cleaners have air flow
   and bag filled sensors which may go bad or get bent or damaged.  Some
   of these can be tested easily with an ohmmeter but the newest computer
   controlled vacuum cleaners may be more appropriate to be repaired by a
   computer technician!

4. Bad motor - not as common as one might thing.  However, worn carbon
   brushes or dirt wedged in and preventing proper contact is possible.
   See the section: "Problems with universal motors".

5. Bad internal wiring - not likely but always a possibility.

  7.90) Vacuum cleaner hose damage

"We have been quoted a price of $100 to replace the hose on our Panasonic
 (Mc-9537) vacuum cleaner. It has a rip in it; next to the plastic housing 
 where the metal tubing starts.  Does anyone know if there is a more 
 economical way to solve this problem?"

I have always been able to remove the bad section and then graft what is
left back on to the connector.  Without seeing your vacuum, there is no way
to provide specific instructions but that is what creativity is for! :-)
It might take some screws, tape, sealer, etc.

$100 for a plastic hose is obviously one approach manufacturers have of
getting you to buy a new vacuum - most likely from some other manufacturer!

Note: Some vacuum cleaners with power nozzles use the coiled springs of the
hose as the electrical conductors for the power nozzle.  If you end up cutting
the hose to remove a bad section, you will render the power nozzle useless.

  7.91) High tech vacuum cleaners?

Excerpt from a recent NASA Tech Brief:

"The Kirby Company of Cleveland, OH is working to apply NASA technology to
 its line of vacuum cleaners.  Kirby is researching advanced operational
 concepts such as particle flow behavior and vibration, which are critical
 to vacuum cleaner performance.  Nozzle tests using what is called Stereo
 Imaging Velocity will allow researchers to accurately characterize fluid
 and air experiments.  Kirby is also using holography equipment to study
 vibration modes of jet engine fans."

I suppose there will be degree-credit university courses in the operation
of these space age vacuums as well! --- sam

  7.92) Dustbusters(tm) and other battery powered hand vacs

These relatively low suction battery powered hand vacuums have caught on
due to their convenience - certainly not their stellar cleaning ability!

A NiCd battery pack powers a small DC permanent magnet motor and centrifugal
blower.  A simple momentary pushbutton power switch provides convenient
on/off control.

Aside from obvious dirt or liquid getting inside, the most common problems
occur with respect to the battery pack.  If left unused and unplugged for
a long time, individual NiCd cells may fail shorted and not take or hold
a charge when the adapter is not plugged back into the wall socket.  Sluggish
operation is often due to a single NiCd cell failing in this way.

See the appropriate sections on "Batteries" and "Motors" for more information.

  7.93) Dustbusters left on continuous charge and battery problems

The low current trickle charger supplied with these battery operated hand-vacs
allow Dustbusters and similar products to be be left on continuous charge so
long as they are then not allowed to self discharge totally (left on a shelf
unplugged for a long time).  Older ones, in particular, may develop shorted
cells if allowed to totally discharge.  I have one which I picked up at a
garage sale where I had to zap cells to clear a shorts.  However, it has been
fine for several years now being on continuous charge - only removed when used.

While replacing only selected cells in any battery operated appliance is
generally not recommended for best reliability, it will almost certainly
be much cheaper to find another identical unit at a garage sale and make
one good unit out of the batteries that will still hold a charge.  It is
better to replace them all but this would cost you as much as a new

The NiCd cells are soldered in (at least in all those I have seen) so
replacement is not as easy as changing the batteries in a flashlight but
it can be done.  If swapping cells in from another similar unit, cut the
solder tabs halfway between the cells and then solder the tabs rather than
to the cells themselves if at all possible.  Don't mess up the polarities!

In the case of genuine Dustbusters, where a new battery is needed and you
don't have a source of transplant organs, it may be better to buy the
replacement cells directly from Black and Decker. They don't gouge you on NiCd
replacements.  B&D is actually cheaper than Radio Shack, you know they are the
correct size and capacity, and the cells come with tabs ready to install.
They'll even take your old NiCds for proper re-cycling.

  7.94) Floor polishers

A relatively large universal motor powers a set of counter-rotating
padded wheels.  Only electrical parts to fail: plug, cord, power switch,
motor.  Gears, shafts, and other mechanical parts may break.

  7.95) Heating pads

Heating pads are simply a very fine wire heating element covered in thick
insulation and then sealed inside a waterproof flexible plastic cover.
Internal thermostats prevent overheating and regulate the temperature.
The hand control usually provides 3 heat settings by switching in different
sections of the heating element and/or just selecting which thermostat is used.

There are no serviceable parts inside the sealed cover - forget it as any
repair would represent a safety hazard.  The control unit may develop bad
or worn switches but even this is somewhat unlikely.  It is possible to
disassemble the control to check for these.  You may find a resistor or diode
in the control - check these also.  With the control open, test the wiring to
the pad itself for low resistance (a few hundred ohms) between any pair of
wires).  If these test open, it is time for a new heating pad.  Otherwise,
check the plug, cord, and control switches.

Extended operationg especially at HIGH, or with no way for the heat to escape,
may accelerate deterioration inside the sealed rubber cover.  One-time thermal
fuses may blow as well resulting in a dead heating pad.  One interesting note:
Despite being very well sealed, my post mortems on broken heating pads have
shown one possible failure to be caused by corrosion of the internal wiring
connections after many years of use.

  7.96) Electric blankets

As with heating pads, the only serviceable parts are the controller and
cordset.  The blanket itself is effectively sealed against any repair
so that any damage that might impact safety will necessitate replacement.

Older style controllers used a bimetal thermostat which actually sensed
air temperature, not under-cover conditions.  This, it turns out, is a
decent measurement and does a reasonable job of maintaining a comfortable
heat setting.  Such controllers produced those annoying clicks every couple
of minutes as the thermostat cycled.  Problems with the plug, cord, power
switch, and thermostat contacts are possible.  The entire controller usually
unplugs and can be replaced as a unit as well.

Newer designs use solid state controls and do away with the switch
contacts - and the noise.  Aside from the plug and cord, troubleshooting
of a faulty or erratic temperature control is beyond the scope of this

  7.97) Humidifiers

There are three common types:

1. Wet pad or drum - a fan blows air across a stationary or rotating
   material which is water soaked.  There can be mechanical problems
   with the fan or drum motor or electrical problems with the plug,
   cord, power switch, or humidistat.

2. Spray - an electrically operated valve controls water sprayed from
   a fine nozzle.  Problems can occur with the solenoid valve (test the
   coil with an ohmmeter), humidistat, or wiring.  The fine orifice may
   get clogged by particles circulating in the water or hard water deposits.
   In cleaning, use only soft materials like pointy bits of wood or plastic
   to avoid enlarging the hole in the nozzle.

3. Ultrasonic - a high frequency power oscillator drives a piezo electric
   'nebulizer' which (with the aid of a small fan) literally throws fine
   droplets of water out into the room.  Problems with the actual ultrasonic
   circuitry is beyond the scope of this manual but other common failures
   can be dealt with like plug, cord, fan motor, control switches, wiring,
   etc.  However, if everything appears to working but there is no mist
   from the output port, it is likely that the ultrasonic circuitry has
   failed.  See the section: "Ultrasonic humidifiers" for more details.

  7.98) Ultrasonic humidifiers

(From: Filip "I'll buy a vowel" Gieszczykiewicz (filipg@repairfaq.org)).

The components of the typical $45 unit are:

* Piezo transducer + electronics (usually in a metal cage - we are talking
  line current here - not safe!).

* Small blower/fan.

* Float-switch.

* Water tank.

The piezo transducer sets up a standing wave on the surface of the water pool.
The level is sensed with a float-switch to ensure no dry-running (kills the
piezo) and the blower/fan propels the tiny water droplets out of the cavity.
A few manufacturers are nice enough to include a silly air filter to keep any
major dust out of the 'output' - do clean/check that once in a while.

Common problems:

* Low output:

  - Minerals from water deposited on surface(s) of the water pool - including
    the piezo. This disrupts/changes the resonance/output of the piezo - and
    you see the effect.

  - Clogged air filter - there should be a little 'trap door' somewhere
    on the case with a little grill. Pop it out and wash the filter found
    therein. Replace.

  - Driver of the piezo going down that hill. Time to get another one or
    look for the warranty card if it applies.
CAUTION: Unless you know what you are doing (and have gotten shocked a
few times in your life) DO NOT play with the piezo driver module. Most
run at line voltage with sometimes 100+V on heatsinks - which are live.

* No output:

  - Dead piezo driver - get a new unit unless under warranty.

  - Dead wire or float-switch or humidity switch or 'volume'... that 
    should be easy - use an ohmmeter and look for shorts/opens/resistance.

  - Dead fan - should still have mist - just none of it getting out.

  - No power in the outlet you're using ;-)

Note: piezo's in general are driven with voltage, as opposed to current. This
explains why you can expect high voltages - even in otherwise low-voltage
circuits. Case in point: the Polaroid ultrasonic sonar modules.

  7.99) Ultrasonic waterfalls?

I don't suppose you are likely to encounter these but if you do, servicing
procedures will be similar to those described in the section: "Ultrasonic humidifiers".

(From: Roger Vaught (vaurw@onramp.net)).

At a local shop they sell small water fall displays made from limestone in a
marble catch basin.  These are made in China. They use a small water pump for
the flow.  

When I first saw one I thought the store had placed dry ice in the cavity
where the water emerged as there was a constant stream of cloud flowing from
it.  Very impressive. It turns out they use the ultrasonic piezo gizmo to make
the cloud.  The driver is a small 3 X 5 X 3 inch box with a control knob on
top.  If you look into the cavity you can see the piezo plate and a small red
LED.  The water periodically erupts into vapor.  I haven't been able to get a
close look at the driver so I can't tell where it is made or if there is a
product name or manufacturer.  They will sell that part of it for $150! 

  7.100) Ultrasonic cleaners

Ultrasonic cleaning is a means of removing dirt and surface contamination from
intricate and/or delicate parts using powerful high frequency sound waves in
a liquid (water/detergent/solvent) bath.

An ultrasonic cleaner contains a power oscillator driving a large piezoelectric
transducer under the cleaning tank.  Depending on capacity, these can be quite

A typical circuit is shown below.  This is from a Branson Model 41-4000 which
is typical of a small consumer grade unit.

               R1        D1
 H o------/\/\-------|>|----------+
         1, 1/2 W  EDA456         |
               C1         D2      |
          |  .1 uF   |  EDA456    |  2  
          |  200 V   |      +-----+---+ T1      +---+------->>------+
          |    R2    |     _|_ C2      )||  o 4 |   |               |
          +---/\/\---+     --- .8 uF D )|| +----+   |               |
          |   22K          _|_ 200 V   )||(         +               |
          |   1 W           -      1 o )||(          )||           _|_
          +-----------------+---------+ ||( O        )|| L1        _x_ PT1
          |           R3    |        7  ||(          )||            |
          |      +---/\/\---+   +-----+ ||( 5       +               |
         C \|    | 10K, 1 W     |    F )|| +---+    |               |
       Q1   |--+-+--------------+  6 o )||     |    |               |
         E /|  |  D3     R4       +---+        +----+------->>------+
          |    +--|<|---/\/\--+  _|_
          |           47, 1 W |  ---       Input: 115 VAC, 50/60 Hz
          |                   |   |        Output: 460 VAC, pulsed 80 KHz
 N o------+-------------------+---+

The power transistor (Q1) and its associated components form an self excited
driver for the piezo-transducer (PT1).  I do not have specs on Q1 but based on
the circuit, it probably has a Vceo rating of at least 500 V and power rating
of at least 50 W.

Two windings on the transformer (T1, which is wound on a toroidal ferrite
core) provide drive (D) and feedback (F) respectively.  L1 along with the
inherent capacitance of PT1 tunes the output circuit for maximum amplitude.

The output of this (and similar units) are bursts of high frequency (10s to
100s of KHz) acoustic waves at a 60 Hz repetition rate.  The characteristic
sound these ultrasonic cleaners make during operation is due to the effects
of the bursts occuring at 60 Hz since you cannot actually hear the ultrasonic
frequencies they use.

The frequency of the ultrasound is approximately 80 KHz for this unit with a
maximum amplitude of about 460 VAC RMS (1,300 V p-p) for a 115 VAC input.

WARNING: Do not run the device with an empty tank since it expects to have
a proper load.  Do not touch the bottom of the tank and avoid putting your
paws into the cleaning solution while the power is on.  I don't know what,
if any, long term effects there may be but it isn't worth taking chances.
The effects definitely feel strange.

Where the device doesn't oscillate (it appears as dead as a door-nail), first
check for obvious failures such as bad connections and cracked, scorched, or
obliterated parts.

To get inside probably requires removing the bottom cover (after pulling the
plug and disposing of the cleaning solution!).

CAUTION: Confirm that all large capacitors are discharged before touching
anything inside!

The semiconductors (Q1, D1, D2, D3) can be tested for shorts with a multimeter
(see the document: "Basic Testing of Semiconductor Devices".

The transformer (T1) or inductor (L1) could have internal short circuits
preventing proper operation and/or blowing other parts due to excessive load
but this isn't kind of failure likely as you might think.  However, where all
the other parts test good but the cleaning action appears weak without any
overheating, a L1 could be defective (open or other bad connections) detuning
the output circuit.

  7.101) Dehumidifiers

Electric dehumidifiers use a refrigeration system to cool a set of coils
which condenses water vapor.  The heat is then returned to the air and
it is returned back to the room.  On the surface, this seems like an
incredible waste of energy - cooling the air and heating it back up -
but it is very effective at removing moisture.  A typical large dehumidifier
will condense something like 30 pints in 24 hours - which, unless you have
it located over a drain - then needs to be dumped by hand.

There is supposed to be a cutoff (float) switch to stop the dehumidifier
when the container is full.  Hopefully, it works (and you didn't neglect
to install it when the unit was new!)

Common problems with these units are often related to the fan, humidistat,
or just plain dirt - which tends to collect on the cooling coils.  The
sealed refrigeration system is generally quite reliable and will never need

An annual cleaning of the coils with a soft brush and a damp cloth is a good
idea.  If the fan has lubrication holes, a couple of drops (but no more) of
electric motor oil should be added at the same time.

The fan uses an induction motor - shaded pole probably - and may require
cleaning and lubrication.  See the section: "Problems with induction motors".

The humidistat may develop dirty or worn contacts or the humidity sensing
material - sort of like a hot dog wrapper - may break.  If you don't hear
a click while rotating the control through its entire range, this may have
happened.  If you hear the click - and the dehumidifier is plugged into
a live outlet - but nothing happens, then there is probably a problem in
the wiring.  If just the fan turns on but not the compressor, (and you have
waited at least 5 minutes for the internal pressures to equalize after
stopping the unit) then there may be a problem with the compressor or its
starting relay (especially if the lights dim indicating a high current).

A very low line voltage condition could also prevent a refrigeration system
from starting or result in overheating and cycling.  A sluggish slow rotating
or seized fan, or excessive dirt buildup may also lead to overheating and
short cycling.

A unit that ices up may simply be running when it is too cold (and you don't
really need it anyway).  Dehumidifiers may include sensors to detect ice
buildup and/or shut off if the temperature drops below about 60 degrees F.

  7.102) Garbage disposals

A garbage disposal is just an AC induction motor driving a set of centrifugal
hammers (they use to use sharp cutters but these were even more dangerous).
The cutters throw the food against an outer ring with relatively sharp slots
which break up the food into particles that can be handled (hopefully) by
the waste system.  However, always use generous amounts of cold water (which
helps to cool the motor as well) and let it run for a while after there is
nothing left in the disposal and it has quieted down.  This will assure a
trouble free drain.  Otherwise, you may be inviting your friendly plumber
over for a visit!

Common problems with garbage disposals relate to three areas:

* Something stuck in grinding chamber - disposal hums or trips internal
  protector (red button) or main fuse or circuit breaker.  Unplug disposal!
  Then use the wrench (or appropriate size hex wrench) that came with the
  disposal to work rotor back and forth from bottom.  If there is no hole
  for a wrench (or you misplaced yours), try a broom handle from above but
  NEVER put your hand in to try to unjam it (there are still relatively
  sharp parts involved).   With the disposer unplugged, you can carefully
  reach in and feel for any objects that may be stuck or which cannot be
  broken up by the grinding action (like forks, toys, rocks, beef bones,
  etc.) and fish these out.  Once free, restore power (if needed) and/or
  reset red button ((usually underneath the motor housing - you may have
  to wait a couple minutes until it will reset (click and stay in).  Then
  run the unit with full flow of cold water for a couple of minutes to clear
  anything remaining from the grinding chamber and plumbing.

* Motor - although these only run for a few seconds a day, motor problems
  including shorted windings or defective rotors are possible.   Assuming
  rotor turns freely, these may include a hum but no movement, repeated
  blown fuses or tripped circuit breakers, or any burning smells.

* Leaking shaft seal - probably what causes most disposals to ultimately
  fail.  The upper seal develops a slight leak which permits water to enter
  the motor housing damaging the bearing and causing electrical problems.
  Symptoms include seized rotor, excessive noise or vibration,  actual
  water leaking from inside the motor housing, burning smells, etc.

* Power switch (built into batch feed models) - wall switches can go bad
  like any other application.  The built in magnetic or microswitch in a
  batch feed disposal can also fail.  Intermittent or no operation may

* Drain blockage - disposal runs but water doesn't get pumped out of sink
  or backs up.  Use plumber's helper (plunger) or better yet, remove U-trap
  under sink and use a plumber's (steel) snake to clear blockage in the
  waste pipe.  NEVER NEVER use anything caustic!!!  First of all, it will
  not likely work (don't believe those ads!).  More importantly, it will
  leave a dangerous corrosive mess behind for you or the plumber to clean
  up.  The plunger or snake will work unless the blockage is so impacted
  or in a bad location (like a sharp bend) in which case a professional
  will need to be called in any case.

Unless you are the truly die-hard doit-yourselfer, repair of disposals is
probably not a good use of your time.  The ultimate reliability of all
but the most obvious and simple repairs is usually unknown and could be
very short.  However, other than time, there is nothing to be lost by
at least investigating the source of the problem.

  7.103) Garbage disposal pops reset button but nothing blocked

Even if nothing is stuck in it, is the rotor free - not too tight?  If you
have that little wrench that comes with many disposers, you should be able
to turn the rotor relatively easily (I would say about 1 foot-pound of
torque or less if your arm is calibrated).  A tight bearing may be the
result of a shaft seal leak - see the next section: "Garbage disposal seizes repeatedly".

The red reset button is a circuit breaker.  Either the motor is drawing
too much current due to a shorted winding or a tight bearing or the breaker
is faulty.  Without an ammeter, it will be tough to determine which it
is unless the rotor is obviously too tight.

If you have a clamp-on ammeter, the current while the motor is running
should be less than the nameplate value (startup will be higher).  If
it is too high, than there is likely a problem with the motor.  As an
alternate you could try bypassing the circuit breaker with a slow blow
fuse of the same rating as the breaker (it hopefully will be marked) or
a replacement breaker (from another dead garbage disposal!.  If this
allows the disposer to run continuously your original little circuit
breaker is bad.  These should be replaceable.

If the bearings are tight, it is probably not worth fixing unless it is
due to something stuck between the grinding disk and the base.  Attempting
to disassemble the entire unit is likely to result in a leak at the top
bearing though with care, it is possible to do this successfully.

  7.104) Garbage disposal is stuck - hums but does not turn

"I need help.  Our garbage disposal is stuck.  It hums but doesn't turn.  If I
 leave it on for more than a few seconds it trips the circuit breaker on the unit.
 Any tips on how to solve this shy of buying a new unit?  The unit is 7 years old."

"I have an ISE In-Sink-Erator (tm), Badger I model.  I tried turning mine on a
 few minutes ago, the motor started then stopped and now nothing happens when I
 flip the wall switch, not even a click."

Of course, first make sure there is nothing jamming it - use a flashlight
to inspect for bits of bone, peach pits, china, glass, metal, etc.  Even a
tiny piece - pea size - can get stuck between the rotating disk and the
the rotor back and forth using the hex wrench that came with the unit or
a replacement (if your unit is of the type that accepts a wrench from below.
If it is not of this type, use the infamous broom handle from above.)

The internal circuit breaker will trip to protect the motor if the rotor
doesn't turn.  Turn off the wall switch, wait a few minutes for the circuit
breaker and motor to cool, and then press the red reset button underneath
the disposal.  If it does not stay in, then you didn't wait long enough or
the circuit breaker itself is defective.  Then, turn on the water and try
the wall switch again (in-sink switch if it is a batch feed model).

Assuming it is still tight with nothing stuck inside and/or jams repeatedly:

(From: Rob-L (rob-l@superlink.net)).

That's about how long it takes for the nut to rust away on the shredder
disc of Insinkerator/Sears units.  My comments will address ISE/Sears
deluxe models with the stainless disc, for those who might have one.

When the nut/washer rusts away, the disc will wobble and get jammed.  With
the power off, try to rock the disc inside the unit. You might need to
wiggle the motor shaft with a 1/4" hex wrench under the unit.  

If you can free things up, and the disc can be rocked, it's the
nut/washer.  When that goes, so does the gasket, and unfortunately it
requires total disassembly of the grinding chamber to replace the little
gasket, because the disc will not come out otherwise.  And if you don't
replace the gasket, water/gunk will run down the motor shaft and into the
motor. When those units go, you're better off to get a new disposer.  

I think they intentionally use a non-stainless steel nut, because
otherwise the units would last a long time.  Even the replacement nuts
will corrode.  The motor shaft will also corrode, but not as fast as the
nut.  With a stainless shaft and nut/washer, the disposer would give many
more years of service.  And that's why they don't make 'em that way. :)

One part that is worth replacing is the mounting gasket.  It's the part
with the flaps that you feed things through.  It gets cut-up and damaged
by chlorine from sink cleaning or dishwasher discharge. (brittle, rough) 
It's a $4 part, usually available at Home Depot next to the new disposers,
and it slips on in a matter of minutes -- you just disconnect the trap,
then drop the disposer down by undoing the retaining ring.  Swap the
gasket, re-attach things, and your sink drain looks brand new.

  7.105) Garbage disposal seizes repeatedly

A garbage disposal that doesn't have anything stuck in the cutting chamber
but seems to be hard to turn or will work with effort until left alone for
a day or two probably has a bad bearing caused by a leak at the shaft seal.
Of course, water gushing out of the lower part of the disposal (or *any*
amount of water dripping from inside the motor housing) is one indication
that there is a leak!  This also represents a safety hazard so the disposal
should be left unplugged and not be used even if it still runs.

By the time the leak is detected, it is probably too late to save the
disposal as corrosion of the steel shaft, excessive wear of the bronze
bushing, as well as possible electrical damage has already occurred.

Realistically, there is nothing that could have likely been done in any
case.  It is virtually impossible to repack such a bearing in such a way
to assure that a leak will not develop in the near future.

  7.106) Garbage disposal replacement (or upgrade)

My general recommendation is to get the approximately $100 1/2-3/4 Hp Sears (ISE
In-Sinkerator(tm) manufactured) unit when it is on sale (which is about every
week).  These now have at least a 4 year warranty.

If your previous garbage disposal was an ISE In-Sinkerator or Sears, then
replacement is usually a 10 minute job if the under-sink plumbing is in
reasonably good condition (doesn't crumble to dust when you touch it).
If the part that mounts to the sink is not corroded and not leaking, I
just leave it alone.  The only tools required are a screwdriver and wire
strippers (possibly) to move the power cord or cable to the new unit and
a screwdriver or socket driver and a large adjustable wrench or pliers to
unscrew the drain pipe and dishwasher connection (if used).  Complete
instructions should be provided with the replacement unit.

  7.107) Sump pumps and utility pumps

Sump pumps come in two major varieties:

1. Pedestal - a motor on top of a 3 foot or so pole drives an impeller at
   the bottom of its long shaft.  Only the base may be submerged.

   These motors are quite reliable but the bearing can rot/rust/sieze at
   the base where it may be under water or at least in a humid environment.

2. Submersible - a motor, usually totally enclosed in a sealed pump
   housing within an oil bath drives an impeller.  The entire unit
   is designed to be fully or partially submerged in the sump hole.

   The casing may leak at the bearing (if not magnetically coupled) or at the
   wire connections.  Repair of these motors is probably not worth the effort.

Utility pumps are often of the submersible variety.

Three types of automatic switches are commonly used:

1. Float/weight on a wire, rod, or string pulls on a spring action toggle
   type switch.  The length of the linkage is adjusted for the appropriate
   low and high water settings.  These will be used mostly with pedestal
   pumps.  If properly sized, this type of switch can be quite reliable - I
   have a sump pump using this type of switch which is easily 30 years old
   at this point without ever having any problems with the switch.

2. Mercury tilt switch sealed inside a rubber float.  By fastening its
   connecting wire to a suitable location, the level of the water will
   cause the float to pivot from horizontal the more vertical.  An enclosed
   mercury switch then controls power to the pump motor.  These are not
   serviceable but replacements are readily available.

3. Diaphragm pressure switch designed to sense the depth of the water from
   the trapped pressure.  As above, these are not really serviceable but
   can be easily replaced by the same or a mercury type (2).

Most common problems are with switches that are no longer reliable or totally
broken.  Universal replacements are generally available since the switch is
not usually an integral part of the motor/pump unit.

  7.108) Toys

Since there are a semiinfinite number of variations on electrically powered
toys, the only comment I have is that these are almost always combinations
of small PM motors, switches, batteries, light bulbs - and totally impossible
to identify electronic components.  With small kids, physical destruction is
probably a much more common occurrence than a part failure!

  7.109) Garage door operators

Typical garage door operators use a 1/3 to 3/4 horsepower induction motor
with a belt drive chain or screw mechanism to move the 'trolley' that actually
grabs the door.  A switch or pair of switches activated at each end of travel
stops the motor and toggles the state (up or down) of the controller.  Door
blockage sensors detect obstructions and stop or reverse travel.  A light
turns on with motor start and stays on for 3-5 minutes thereafter, controlled
by a simple timer.

Parts of a typical garage door operator (chain drive).  Details may differ
on operators with worm screw or other drive schemes.

1. Motor - single phase induction motor of about 1/2 horsepower at 862 or 1725
   (or so) RPM.  It is electrically reversible with a large ratio V-belt drive
   (probably about 25:1 for a 1725 RPM motor between motor shaft and chain

2. Chain or screw drive - often needs lubrication.  Make sure grease will
   not harden at low temperatures if relevant (e.g., Lubriplate).

3. Limit switches - set top and bottom positions of door.

4. Safety stop - a means of sensing when excessive force is required to move
   the door.  Some types use a compliant motor mount such that excessive
   torque will result in a twist which closes a set of contacts to reverse
   or stop the door.

5. Logic controller - a some relays or a microcontroller.

6. Remote receiver - a radio receiver tuned to the frequency of the hand
   unit.  Logic here or in the controller checks the transmission to 
   determine if the codes match.  More sophisticated units employ a
   pseudo-random code changing scheme to reduce the chance of code theft.
   This is usually in a box on the wall connected to the motor unit by a
   pair of wires.

7. Light bulbs and timer - in many Sears as others, the timer is a bimetal
   strip heated to operate a set of contacts.  The on-time is determined by
   how long it takes for the bimetal strip to cool.  These fail after about
   10 years but replacements are readily available.

  7.110) General garage door operator problems

1. No response from remote or local buttons.  Test power to both the motor
   unit and control box (they may be separate) outlets.  The operator or
   some other device might have blown a fuse or tripped a circuit breaker.
   Verify that the connection between the wall box and the motor unit is in
   tact - check the screw terminals on the motor unit - a wire may have fallen
   off.  Check the circuit breaker (red button) on the motor unit - an overload
   or an undetected cycling condition (an obstruction causing the door to keep
   going up and down continuously) may have tripped it.  Warning: pressing
   this button may result in the door starting to move immediately.

2. Local (inside) buttons work but remote unit is dead.  Check and/or replace
   batteries in the remote unit, confirm that the the code settings have not
   accidentally changed (unit dropped, for example), go through the set up
   procedure outlined in your users manual.  Find a cooperative neighbor with
   the same model and try their remote unit (after writing down their settings
   and reprogramming it for your door).  If this works, your remote unit is
   bad.  If this does not work, you have a receiver problem.

3. Motor operates (you can hear it) but door does not move.  This can be caused
   by a broken or loose belt, snapped door counterbalance spring, locked door,
   disconnected or broken trolley, logic problems causing the motor be turning
   in the wrong direction, and other mechanical problems.  If the motor
   runs for about the normal time, then the trolley is probably moving but
   not attached to the door.  If it runs until forever or the overload pops,
   then a broken belt is likely.

4. Door opens or closes part way and reverses, stops, or twitches back and

   * The tracks may need lubrication, there may be an obstruction like a broom
     that fell over into the vertical rails.

   * The gear timing may be messed up.  The upper and lower limits may be
     determined by switches operated from a cam separate from the trolley that
     moves the door.  If you just reassembled the mechanism, this is a likely

   * The safety stop sensors may be set to be too sensitive.

   * In extremely cold weather, the grease may simply be too viscous or just
     gummed up.

5. Door opens and closes at random.  There can be several possible causes:

   * A neighbor has a similar model and has selected the same code (probably
     the factory default - did you actually ever pick your own code?).

   * Interference from nearby high power amateur, CB, or military or commercial
     radio transmitters may be  confusing the receiver.  Suggest to them that
     they relocate :-).

     Are there such things as IR remote controls for garage door openers
     instead of the usual radio frequency variety?

   * The push button switch on your one of your remotes or receiver module
     is defective - a weak or broken spring - and it is activating the door
     due to vibration or just because it feels like it.  Test the switches.
     On the hand units, you can just remove the batteries for a day and see
     if the door stops misbehaving.

  7.111) Garage door operator light does not work correctly

Assuming the unit otherwise operates normally and you have tried replacing
the light bulb(s):

For many types (Sears, Genie, etc.), there is a thermally operated
time delay consisting of a coil of resistance wire, a bimetal strip,
and a set of contacts.  When the operator is activated, power is applied
to the heater which causes the bimetal strip to bend and close the
contacts turning on the light.  Due to the mass of the bimetal strip,
it takes a couple of minutes to cool down and this keeps the light on.

The most common failure is for the fine wire in the heater to break at
some point.  If you can locate the break, it may be repairable at least
as a temporary solution.  You cannot solder it, however, so a tiny
nut and bolt or crimp will be needed.  However, sticking contacts resulting
in a light that does not always go off are also possible.  Cleaning the
contacts may help.

This part is very easily accessed once the sheetmetal cover is removed.
It is probably somewhere in the middle of the unit fastened with three
screws.  Just remember to unplug the operator first!

Depending on the manufacturer, the original part may be available.  I
know that it is for Sears models.

You could also use a time delay relay or a solid state circuit (RC delay
controlling a triac, for example) but an exact replacement should be just
a whole lot less hassle.

  7.112) Garage door operator loses track of where it is

You press the button to close the door and it works fine.  However, next
time you press the button to make the door go up and it tries to go down into
the ground.

When it gets to the end of the track - be it at the top or bottom, there
must be something that it trips to shut down the motor.  At the same time,
this is supposed to set things up so that the next activation will reverse
the door.

Does the door stop and shut off when it reaches the end or does it eventually
just give up and trip on the safety?

When it trips the switch to stop at the end of its travel, some mechanism
is toggled to change the 'state' of the door logic so that it knows to
go up the next time it is activated.  It is probably this device - be it a
latching relay, mechanical two position switch, or a logic flip flop - that
is not being properly toggled.

I would recommend attempting to determine what device that switch is actually
supposed to toggle - it probably is in the operator unit itself (not the
control box).

  7.113) Garage door remotes behave differently

"I've got 2 Genie garage door remotes.  One of them works from about 100 yards
 away; the other I almost have to be right next to receiver.  I suspect that
 the antenna is the problem; either too short, or blocked by something."

First compare the antennas on the two remotes.  If they are the same and
there are no broken connections, your problem lies elsewhere.  The chance
of the wire itself being bad is pretty slim.

It could also be that the receiver and transmitter frequencies are not quite
identical.  If the remote units have been abused, this is more likely.  I
don't know about Genie but my (old) Sears has trimmers and I was able to
adjust it *very* slightly to match that of the receiver and boost sensitivity.

CAUTION: If you try this (1) mark the exact position where it was originally
and (2) do it only on the transmitter that has the problem.  This will minimize
the possibility of shifting the frequency to where it might interfere with
other devices.  See the section: "Adjusting garage door operator remote unit"
for more information.

  7.114) Adjusting garage door operator remote unit

This situation may arise if one hand unit operates normally but the other
has a very short range.  If you have only one hand unit, it might also be
the problem though not likely to have just happened on its own - either
it was improperly set up at the factory (if new) or hand unit was dropped
once too often.

It should not work at all if the switches are set improperly.  In such a
case, first test and/or replace the battery.  If this does not help, check
the switch settings.

The tuning is done via a variable capacitor trimmer (probably).

There will probably be a trimmer inside the hand unit (don't touch the one
in the receiver).  Position yourself at a reasonable distance and use a
plastic tool to adjust it until the door operates while holding the button
down.  The door will respond at increasing distances as you approach the
optimal setting.

Note: mark the original position first in case this has no effect!

This assumes there is an adjustment - if there is none, you may have an
actual electronic failure, bad connections, etc.

  7.115) Improving sensitivity of garage door openers receivers

Where a garage is constructed with aluminum siding, the remote signal may
be significantly attenuated and of insufficient strength to activate the
receiver module (inside the garage) of the opener at any useful distance
or at all.  Assuming the system operates normally otherwise (i.e., activation
is normal with the door open), two approaches (either or both together) can
be taken to solve this problem:

1. Locate the receiver module (well, actually, its antenna) in an area of
   unsided wood, glass window, or other non-metallic area of the building.
   Note that construction insulation may use aluminum foil as part of its
   vapor barrier so there could be problems even in an area with no siding.

2. Extend the antenna on the receiver module.  This may not always work but
   is worth a try.  A 1 or 2 foot length of copper wire may help dramatically.

3. There are external antenna kits available for some door openers.  The
   antenna goes outside, and connects to the receiver through a hole in
   the wall using coaxial cable.  You will probably have to go directly
   to the manufacturer of your garage door opener or a garage door opener
   service company.

  7.116) Universal remote/receiver units for garage door operators

So you lost your garage door remote or it got run over by your 4x4 :-).  Or,
it just expired due to age.  There are alternatives other than an entire new
operator if the remote is no longer available:

(From: Kirk Kerekes (redgate@tulsa.oklahoma.net)).

Go to a home center, and wander over to the garage door openers. Nearby,
you will find GDO accessories, and among the accessories will be a universal
replacement remote kit that includes a receiver, a transmitter and possibly
a power supply. For about $40, you can by and install the receiver in place of
the existing receiver. If your home center carries Genie openers, you can even
get an Intellicode add-on unit that uses Genie's scanner-proof code-hopping

  7.117) Garage door operator doesn't work reliably in cold weather

First, check the lubrication.  The most common problem is likely to be
gummed up grease in the chain drive (if used) or the bearings of the
rollers.  Note: the track itself generally doesn't require lubrication.
Increasing the safety override force settings may help but are not a wise
solution as the door will then be more of a hazard to any legitimate
obstructions like people and pets.

Another possibility is that the motor start/run capacitor has weakened
and is not permitting the motor to provide the proper torque.  You can
test the capacitor if you have a DMM with a capacitance scale or LCR meter.
Better yet, just replace it.

  7.118) Chamberland garage door opener repair?

"My remote broke for my very old (defunct) chamberlain automatic garage
 door opener.

 Chamberlain tech support told me they suggest I buy a whole new unit. Is
 there any other way to make my door usable with a different remote, or
 some other arrangement?"

(From: Panayiotis Panayi (panikos@mishka.win-uk.net)).

Which Chamberlain operator is it, i.e. which model number. You can
buy the handsets for Chamberlain operators up to 5 years old. If it
is older you will have to buy a new Rx & Tx for it. Most operators
have three screw terminals  on the back for the attachment of Rxs.
The old Chamberlain operators conformed to this. The new ones have
the Rx built onto the main PCB inside the operator and have 4
screws externally for pushbuttons and infra red safety beams. If
yours has 4 screws you will have to provide a separate PSU for the
new Rx or solder two pieces of wire after the step down
transformer on the PCB. You must do it before the rectifiers.
Otherwise the current drain from the Rx will be too big for them.
Besides almost all modern separate Rxs take 24 VAC.

  7.119) Garage door operator security

While manufacturers of garage door operators make excellent claims of
security, this is of no value if you don't take advantage of whatever
features are included in your unit. 

If there is access to your house from the garage, this security is even more
critical.  Once inside the garage, a burglar can work in privacy at their
leisure - and a nice set of tools is probably there for their convenience
in getting through your inside door!  Filling up a good sized car or truck
with loot - again in complete privacy - drive out and close the door behind.
No one will be the wiser until you get back.

1. DIP switches.  Many garage door operators use a set of 8, 12, 16, or
   more little switches to set the codes of the remote and base unit.
   If you have never set these, then your are probably still using the
   manufacturer's default - and all instances of the same model probably
   have the same code!  Change it to something random - pick a number
   out of a random page in a telephone directory or something like that.
   Do not select something cute - others, perhaps with not totally honest
   intentions - will think the same way.  You don't have to remember it so
   an arbitrary totally random setting is fine.  However, even the types with
   24 switches - that is over 16 million possible codes - can be sniffed:
   a relatively simple device can monitor your transmission as you open the
   door and program a special remote unit to duplicate it.

2. More sophisticated units incorporate a scheme whereby the codes change
   each time the operator is used in a pseudo-random manner which is almost
   impossible to duplicate.  Even sniffing such a code is of no use as the
   next instance is not predictable.

3. Don't leave your remote unit prominently displayed in your car - it is
   an inviting target.  Theft is not necessary - just a moment to copy down
   the switch settings may be enough.  Lock your car!  Also, leave a bogus
   remote unit in plain view (from your previous operator).

4. Just because the codes are secure doesn't mean that you are safe.  The
   keylocks that are present on many operators to open the door from the
   outside are pretty pathetic.  They can be picked in about the same time
   it takes to use a key - with ordinary tools - or often with any key that
   will fit the keyhole.  My advice: replace with a high quality pick
   resistant keyswitch.  A well designed electronic lock may be best.  When
   going away for an extended period, use the physical lock on the garage
   door itself as added protection and unplug the garage door operator.

  7.120) Identifying unknown transformer ratings in garage door operator

In a garage door operator, the transformer likely powers the controller
and receiver.  If you can look at where its outputs go, you may be able to
infer something about the voltage even if the transformer is a charred mass.

* If there are AC relays in the box, they almost certainly run off the
  transformer and their coil voltage will be the same if it is the only

* Check the capacitors in the power supplies of the controller and/or
  receiver.  They will give an indication of the approximate secondary
  voltage of the transformer.  Their voltage rating will typically be
  1.5 to 2 times the RMS of the transformer.

* Many of these transformers include a thermal fuse under the outer wrappings
  of insulating material.  These may fail from old age or due to a fault.
  If the transformer works fine without overheating when replaced (or bypassed
  temporarily on a fused circuit), then it may be fine.  However, shorted
  windings can cause a thermal fuse to blow and there is then no electrical
  test that will reveal the proper output voltage.

* Disassemble the transformer and count the number of turns of the primary
  and secondary windings.  The ratio multiplied by 115 is the output voltage.

* Get a 24 V transformer (it is probably not more than this) and connect its
  primary to a Variac and its secondary to the opener.  Slowly increase the
  variac  until everything works. (check every volt or so from 5 to 24).
  Measure the output voltage of the transformer, add 10-20%, you've probably
  got the secondary rating.  If it is near a standard value like 12 or 24,
  this is most likely correct.

* Buy a new opener.

  7.121) Electromechanical doorbells and chimes

Most of these consist of a low voltage transformer powered directly from
the house wiring providing 10 to 20 VAC at its output, one or more switches
for the front door(s), one or more switches for the back door(s), and an
electromagnetic chimes unit.

All of the switches for a given location (i.e., inside and outside the storm
door) are wired in parallel.  There will be three terminals on the chimes
unit - Common (C), Front (F), and Back or Rear (B or R).  This notation may
differ slightly for your unit.  Typical wiring is shown below.  An optional
second chimes unit is shown (e.g., in the basement or master bedroom - more
can be added in parallel as long as the bell transformer had an adequate VA

             Bell Transformer                         Chimes
          H o----+                                     Unit
                  )||       X      _|_ Front door        F
                  )|| +-----+------- --------------------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B
   (Junction box) )||(      +------- --------------------o
                  )||(      Y                            C
                  )|| +----------------------------------o
          N o----+

* The primary side of the transformer is generally wired permanently inside
  a junction box.  This could be almost anywhere but the most common location
  is near the main electrical service panel.

* The common goes to terminal 1 of the transformer (the designation 1 and 2
  is arbitrary - it may not be marked).

* All the front door buttons are wired in parallel and this combination
  connects between terminal 2 of the transformer and the F terminal of the
  chimes unit.

* All the back door buttons are wired in parallel and this combination
  connects between terminal 2 of the transformer and the B or R terminal of
  the chimes unit.

Where the pushbuttons are lighted, a small incandescent bulb is wired across
the switch contacts and mounted inside the button unit.  It is unlikely that
this bulb will ever burn out since it is run at greatly reduced voltage.
However, if the button does not light but the bell works, this has happened.
Replace the pushbutton/light combination - locating a replacement bulb may
not worth the effort though Radio Shack is supposed to have something that
will work.

Most 'not-chiming' problems are due to the one or more of the following:

* Defective switches - these do go bad due to weather and use.  Test with
  a multimeter on the AC voltage range.  You should see the transformer voltage
  across the switch when it is not pressed and near 0 voltage across it
  when it is pressed.  If only one location does not work, a defective switch
  is likely.  Sometimes the wires just come loose or corrode at the terminals.
  These can be cleaned - with fine sandpaper if necessary - and reconnected.

  Note: where multiple switches operate the chimes from similar locations,
  multiple wires may be connected to each switch terminal.  Don' mix these up
  or lose them inside the wall!

* Bad connections.  These could be anywhere but unless you just did some
  renovation which may have damaged the wiring, the most likely locations
  are at the switches, transformer terminals, or chimes.  However, this
  sort of installation might have been done by just twisting wires together
  when extra length was needed and these can go bad.  They could be anywhere.
  Good luck finding the corroded twists!  Then, use Wire Nuts(tm) or solder
  them together to assure reliability in the future.

  If just a single location doesn't work, that should narrows down the problem.
  If only one switch does not work, first test the switch.  If disconnecting
  the wires from the switch does not result in full transformer voltage across
  the wires, then there is a bad connection between you and the transformer,
  the transformer has no power, is defective, or there is a short circuit

* Incorrect wiring at chimes unit.  This commonly happens when someone replaces
  the chimes unit and forgets to label the wires :-(.  It is often difficult
  to follow the wires since they pass through door jams, finished basement
  ceilings, and may not be color coded.  But checking it is easy to with a
  multimeter or the chimes themselves.  An assistant would be helpful - else
  you can just short across the front or back buttons as required below.

  1. Disconnect the wires from the chimes unit terminal block.

  2. Have your assistant press the front door button.

  3. Determine which pair of wires has full voltage - use the multimeter or
     touch them between C and F on the chimes unit.  Make a note of which ones
     they are.  One of these wires is will be C and the other is F.

     Note: due to coupling between the wires, there may be some voltage across
     all combinations.  The most will be across the relevant one (and this will
     be the only combination that will sound the chimes if you are using them
     as a voltage indicator).
  4. Have you assistant press the back door button.

  5. Determine which pair of wires now has voltage.

  6. Connect the wire that is the same as one of those in (3) to the C
     terminal, the other wire of the pair to B, and the remaining wire to F.

* Bad transformer or loss of power to transformer.  The transformer will
  often be located near the main service panel but not always.  Sometimes it
  is a challenge to locate!  To test, proceed as follows (this can be done
  with power on - the low voltage is safe but test first to make sure you
  have the correct transformer!):

  1. Disconnect one of the wires from its output terminals and then test across
     it with a multimeter on the AC voltage range.  There should be the full
     rated transformer voltage across these terminals (actually, it will
     probably be 10 to 20 percent greater).  The rated voltage of the
     transformer should be marked on it somewhere.

     - If there is voltage and it is approximately equal to the transformer's
       rated voltage, the transformer is probably good.

     - If there is none, check for a blown fuse, tripped breaker, or tripped
       GFCI; some other equipment may have overloaded the circuit.  Actual
       failure of the transformer blowing a fuse or tripping a breaker is

       A quick test to determine if the transformer is being powered is to
       feel it!  The transformer should be warm but not hot to the touch.  If
       it is stone cold, either there is no power or a bad connection in the
       input line) circuit.

     - If there is voltage and it is approximately equal to the transformer's

     - If the voltage is much lower than the rated voltage, the transformer
       may be bad.  In this case, it will likely be quite hot due to a short
       circuit inside.

  2. Assuming the voltage checks out, reconnect the wire your previously

  3. If it is now low or 0, there is a short circuit somewhere.  Note: a short
     on the secondary of this type of transformer will cause it to run quite
     hot but may not result in a blown fuse or tripped breaker or even any
     permanent damage to the transformer.

  4. If the chimes sound as you reconnect the wire, there is a short in or
     at one of the pushbutton switches or associated wiring.

  5. If the voltage remains the same, then the transformer is probably good
     and the problem lies elsewhere - bad switch, bad connection, defective

* Dirty or defective chimes.  Most common problems are not electrical but
  mechanical - the plungers that strike the actual chime or gong do not move
  freely due to dirt and grime (especially in a kitchen location) or corrosion.
  Usually, wiping them clean or some light sanding will restore perfect
  operation.  Do not lubricate as the oil will just collect crud and you will
  be doing this again in the near future.  If they move freely, then you have
  an electrical problem.  Also note that these chimes are designed to be
  mounted with the plungers moving vertically.  There is likely a 'this side
  up' indication on the unit - if you are experiencing problems with a new
  installation in particular, verify your mounting!

  Test for voltage between the Common and Front or Back terminals when the
  appropriate button is pressed.

  - If correct voltage is present, disconnect the non-common wire and check the
    resistance between the Common and the terminal for the chime that is not
    working - it should be reasonably low, under 100 ohms.  If the resistance
    is infinite, the coil is open.  Unless you can locate the broken wire, the
    chimes unit will need to be replaced.

  - If the voltage is missing, the problem is probably elsewhere.

  - If the voltage is low, there may be a partial short in the coil, the
    transformer may be underrated for your chimes (not all chimes take the
    same amount of power), or there may be a high resistance somewhere else
    in the wiring.

  7.122) Adding an additional set of chimes

There are at least two ways of doing this (though the first one is more
straightforward and intuitive and therefore generally preferred).

1. Locate the wires going to the first chimes unit.  There will be either 2
   or 3 (both front and back door).  Connect the new chimes unit to these
   same wires in parallel:

             Bell Transformer                         Chimes    Chimes
          H o----+                                    Unit 1    Unit 2
                  )||       X      _|_ Front door        F         F
                  )|| +-----+------- --------------------o---------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B         B
   (Junction box) )||(      +------- --------------------o---------o
                  )||(      Y                            C         C
                  )|| +----------------------------------o---------o
          N o----+

   The only concern is whether the existing transformer that operates the
   chimes has enough capacity - you may need to replace it with one with a
   higher 'VA' rating (the voltage rating should be the same).  These are
   readily available at hardware and electrical supply stores and home

   Some people might suggest just paralleling an additional transformer across
   the original one (which may be possible if the output phases match).  I
   would really recommend simply replacing it.  (This is probably easier
   mechanically in any case.)  Unless the transformers output voltages as
   designed are identical, there will be some current flowing around the
   secondaries at all the times.  At the very least, this will waste power
   ($$) though overheating is a possibility as well.

2. Each additional chimes unit or group of chimes units can use its own
   transformer but share the doorbell pushbuttons.  Just wire point 'X' of the
   transformers together and each point 'Y' separately to the C (common)
   terminal on its respective chimes unit(s):

             Bell Transformer                         Chimes    Chimes
          H o----+                                    Unit 1    Unit 2
                  )||       X      _|_ Front door        F         F
                  )|| +-----+------- --------------------o---------o
                  )||(      |  
       115 VAC    )||(      |      _|_ Back door         B         B
   (Junction box) )||(      +------- --------------------o---------o
                  )||(      Y                            C         C
                  )|| +----------------------------------o    +----o
                  )||                                         |
          N o----+        From output Y of identical o--------+
                           second bell transformer
                           (H, N, X, wired in parallel)

   However, since the 'Y' outputs of the transformers are connected at all
   times to the 'C' terminals of the of the chimes units AND the 'X' outputs
   are tied together, any voltage difference between the 'Y' outputs will
   result in current flow through the chimes coils even if no button is
   pressed.  Thus, the transformers must be phased such that there is no (or
   very little) voltage between 'Y' outputs.  Test between 'Y' outputs with a
   multimeter set on AC Volts after you have the transformers powered: if you
   measure about double the transformer voltage rating (e.g., 32 VAC), swap
   ONE set of transformer leads (input or output but not both) and test again.
   If it is still more than a couple volts, your transformers are not matched
   well enough and you should purchase identical transformers or use the
   approach in (1), above.
Note: For either of these schemes, beyond some number of chimes units, the
current rating of the pushbutton switches will be exceeded resulting in early
failure.  However, this should not happen unless your house is similar in size
to Bill Gates' mansion.

* Another alternative:  If you have an unused baby monitor type intercom (your
  kid is now in college), stick the transmitter next to the main chimes and put
  the receiver in your workshop or wherever you want it :-).

  7.123) How to add an addition button to a door bell

Refer to the diagram in the section: "Electromechanical doorbells and chimes",

Another button can be added in parallel with any of the existing ones (i.e.,
between points X and F or X and B in the diagram).  The only restriction is
that you may not be able to have more than one lighted button in each group
as the current passing through the lighted bulbs may be enough to sound the
chimes - at least weakly.

If you cannot trace the wiring (it is buried inside the wall or ceiling)
the only unknown is which side of the transformer to use.  If you pick the
wrong one, nothing will happen when you press the button.

  7.124) Wireless doorbells or chimes

The transmitter and receiver portion of these units are virtually identical
to those of garage door operators.  See the relevant sections on those units
for problems with activation.

The bell or chimes portion may be either an electromechanical type - a coil
forming an electromagnet which pulls in a plunger to strike a gong or bell.
See the section: "Electromechanical doorbells and chimes".

Others are fully electronic synthesizing an appropriate tone, series of tones,
or even a complete tune on demand.  Repair of the electronics is beyond the
scope of this document.  However, there are several simple things that can
be done:

* Check for dead batteries and dirty battery contacts in both the pushbutton
  and chimes unit.

* Confirm that the channel selection settings have not accidentally been
  changed on the pushbutton or chimes unit.  Flick each switch back and
  forth (where switches are used) just to make sure they are firmly seated.

* Check for improper programming or program loss due to a power failure (if
  AC operated) on units that are more sophisticated than a personal computer.

  7.125) Doorbell rings on its own

* For mechanical chimes, this is almost certainly an intermittent short
  circuit in the button wiring or a defective button.  First check or replace
  the outside pushbutton switches as this is the most likely location due to
  environment and small multilegged creatures.

* For electronics chimes, the problem could either be in the transmitter(s) or
  chimes unit or due to external interference.  Someone in your vicinity could
  have the model also set to the default code (which is probably what you
  have, correct?).

  First, remove the batteries or kill power to all transmitters and wait see if
  the problem still occurs.

  - If it does, either the chimes unit is defective or there is an external
    source of interference.

  - If it now behaves, try each one individually to identify the culprit.
    In some cases, a low battery could produce these symptoms as well.

  7.126) Old garage door operator guts for wireless chime

Don't toss the electronic remains of that old garage door operator.  It would
probably be possible to use it as the basis for a wireless doorbell.  Instead
of starting the motor, use its output to enable an electronic chime or buzzer.
The RF transmitter and receiver for a wireless chime is virtually identical
to that of a typical garage door operator.

  7.127) TV antenna rotators

These consist of a base unit with some sort of direction display and knob
and a motor unit to which the TV antenna is mounted.  Of course, the
troubleshooting of these installations is complicated, of course, by the
remote and somewhat inaccessible location of the motor unit :-(.  Before
climbing up on the third story roof, confirm that you haven't lost power
to the motor unit and/or base station and that the connections between
them are secure.

A common type of motor that may be used in these is a small AC split phase or
capacitor run induction motor.  The relative phase of the main and phase coils
determines the direction.  These probably run on 115 VAC.  A capacitor may
also be required in series with one of the windings.  If the antenna does not
turn, a bad capacitor or open winding on the motor is possible.  See the
chapter: "Motors 101" for more info on repair of these types of motors.

The base unit is linked to the motor unit in such a way that the motor
windings are powered with the appropriate phase relationship to turn the
antenna based on the position of the direction control knob.  This may
be mechanical - just a set of switch contacts - or electronic - IR detectors,
simple optical encoder, etc.

Chapter 8) Power Tools

  8.1) Types of motors found in power tools

A variety of motor types are used depending on the type of tool.  AC powered
portable tools usually use a universal motor due to it high power/weight
ratio and ease of electronic speed control.  Cordless tools usually use a
high performance permanent magnet DC motor.  Stationary power tools almost
always use some form of AC induction motor except where variable speed
is required.  

See the sections on these types of motors for more details than the following
summaries provide.

  8.2) Motors in AC line operated portable tools

Line operated portable (corded) power tools usually use a universal type
AC motor providing 3,000 to 30,000 RPM at the motor shaft.  For the same
power rating, these will be significantly lighter than an induction motor.

A single or multiple stage gear reducer drops the relatively high speed
at which these motors are most efficient to whatever the tool actually
requires, increasing the torque as well.

Universal motors can also be speed controlled relatively easily using a
variant of a simple light dimmer type circuit.  Excellent torque is
maintained over a very wide range extending to nearly 0 RPM.

  8.3) Motors in cordless power tools

These are usually high performance permanent magnet DC motors using advanced
high strength and exotic magnetic materials.  They are very compact and light
weight for their power output.  As with all DC (brush type) motors, brush
wear is a common problem.

Speed control is easily accomplished by low cost electronic circuits which
chop the power (pulse width modulation) rather than simply using a rheostat.
This is much more efficient - extremely important with any battery operated

  8.4) Motors in stationary power tools

Stationary power tools which do not require continuous speed control will
generally use some type of AC induction motor - split phase or capacitor
start/run.  The motors generally operate at a fixed speed of around either
1725 or 3450 RPM (U.S., 60 Hz power).  Stepped pulleys or continuous mechanical
speed/torque changers are used to obtain (usually) lower work piece speeds.

For example, a typical drill press may have one or two sets of stepped
pulleys providing 3 to 15 or more speeds by changing belt positions.  A
continuously variable cone drive is also available as an option on some
models.  This is extremely convenient but does add cost and is usually not
found on less expensive models.

An internal thermal overload protector may be incorporated into larger
motors.  WARNING: this may be self resetting.  If the tool stops on its own,
switch off and unplug it before attempting to determine the cause.

Generally, these induction motors are virtually maintenance-free though
cleaning, tensioning, and lubrication may be required of the drive system.

However, electronic speed control of induction motors, while possible,
is relatively complex and expensive requiring a variable frequency
variable voltage power supply.  Therefore, universal motors may be used
on stationary tools like scroll saws with continuously variable electronic
speed control.

  8.5) About horsepower ratings

One horsepower is equal to 746 watts of electrical power (100% efficiency).
Therefore, the most you can get continuously from a normal 115 V 15 A outlet
is about 2 HP.  Any claims (for air compressors, for example) of higher
ratings on a normal outlet are totally bogus.  Companies such as Sears
(Craftsman) like to specify 'Reserve Power' for their power tools which
as best as I can determine refers to the power available for a short time
and may relate to the mass - and inertia - of the rotating parts but not
the continuous power available.  This may be useful to help saw through
a tough knot in a piece of hardwood but may not be terribly meaningful for
a wet/dry vacuum!  Therefore, pay most attention to the continuous power
ratings if they can be found anywhere.  A good indication is probably the
maximum amps required for the electrical service.

As with over-the-counter drugs, extra strength does not necessarily translate
into faster relief, higher current does not always mean better performance,
and horsepower ratings much above what you would compute from V x A may be
more of a marketing gimmick than anything really beneficial.

  8.6) Cords for AC line operated portable power tools

Really old power tools had two wire cord plugs and no safety ground yet were
of all metal (solid and heavy!) construction.  I would recommend that as
a matter of policy, these be retrofitted with a 3 wire grounded cordset.

Newer ones have the grounded cordset while the newest 'double insulated
tools' are of mostly plastic construction and are back to a 2 wire ungrounded

As with any electrical appliances, inspect cords regularly and repair or
replace any that are seriously damaged - if the inner wiring is showing,
nicked, or cut; if the plug is broken or gets hot during use, or where
the cord is pulled from or broken at the strain relief.

  8.7) Portable drills

The portable electric drill (now the rage is cordless) is probably one of
the two first tools that any handyman should own (the other being a saber
saw).  It is used for many things in addition to drilling little holes -
drilling large holes, sanding, polishing, driving screws, etc.  Therefore,
these tools get a lot of use - and abuse.

  8.8) AC line powered drills

An AC line powered electric drill is just a universal motor with a two stage
(typical) gear reduced powering a chuck to hold the drill bit or attachment.
A continuous range speed control with a reversing switch is now standard
on most AC line powered drills.

Typical problems include:

* Worn bearings.  These may be replaceable.  Also see the section: "Upgrading the bearings on a Craftsman drill".

* Worn motor brushes.  Replacements should be available. from the manufacturer
  or a motor/appliance repair shop.

* Broken or chipped gears.  This is rare under normal conditions but
  if the drill was abused, then failure is possible.

* Bad cord or plug.  Repair or replace for safety reasons.

* Bad speed controller/reversing switch.  Replacement trigger assemblies
  are available but may cost half as much as an entire new drill.  One
  common wear item is the linear potentiometer operated by the trigger
  and this is not likely to be a standard component.  The drill may work
  fine as a single speed model if this control fails.  You could always
  use an inexpensive external motor speed controller in this case.

* Bad motor.  Failures are possible but unless abused, not nearly as common
  as other simple problems like bad brushes or bearings.  It may not be cost
  effective to replace a bad armature or stator unless this is an expensive
  high quality drill or you have a similar model available for parts.

* Rusted or gummed up chuck. (Or, lost chuck key!).  The chuck is replaceable.
  Depending on type, it may mount with a right or left hand screw thread and
  possibly a right or left hand retaining screw through the center.  See the
  owner's manual to determine what your drill uses as you could be attempting
  to tighten rather than loosen the chuck if you turn the wrong way.  If by
  some slight chance you do not have the owner's manual :-), a reversible drill
  will usually have a left hand (reversed) thread on the chuck and a
  retaining screw with a right hand (normal) thread.  A non-reversible drill
  will only have a right hand thread on the chuck and probably no retaining
  screw.  There may be a hole to insert a locking rod to prevent the shaft
  from turning as you attempt to loosen the chuck.  Inserting the chuck key
  or a suitable substitute and gently tapping it with a hammer in the proper
  direction may be useful as well to free the chuck.

  A gummed up but not too badly rusted chuck can be rescued with penetrating
  oil like WD40 or Liquid Wrench: spray it into the chuck, let it sit for few
  minutes, then use the chuck key to start working it back and forth.  Pretty
  soon it should be free - rotate through its entire range back and forth.
  Spray and spin a couple more times and it should be fine for another 20.000

  8.9) Upgrading the bearings on a Craftsman drill

Very inexpensive models (like the $30 Father's day specials) may use sleeve
bearings in various locations instead of better quality longer lived ball or
roller bearings.  One particular bearing tends to deteriorate rapidly,
especially if the drill is used for sanding or in dusty work environments
(as opposed to clean rooms :-) ).  This is the motor bearing at the handle
end.  The lubrication dries out or is absorbed by dust particles, the bearing
runs dry, wears, and fails with an ear shattering squeal.  Even if you use ear
plugs, the speed and power are not adequate as the motor is laboring and
overloaded and motor failure would result from prolonged operation.

I have upgraded a couple of these drills to ball bearings.  The substitution
is straightforward requiring disassembly of the drill - removing of the
front gear reducer and then one side of the case.  At this point, the old
sleeve bearing is easily freed from its mounting (just the plastic of the
case) and pulled from the shaft.  The shaft is likely undamaged unless you
attempted to continue running the drill even after going deaf.

The drills I upgraded had bearings that were 7/8" OD, 5/16" thick, and with
a 5/16" ID center hole.  The old ones were worn by almost 1/32" oversize
for the center hole but the motor shaft was undamaged.  I found suitable
replacement double sealed ball bearings in my junk box but I would assume
that they are fairly standard - possibly even available from Sears Parts as
I bet they are used in the next model up.

If the gear reducer needs to come apart to access the motor, take note of
any spacer washers or other small parts so you can get them back in exactly
the correct locations.  Work in a clean area to avoid contaminating the
grease packing.

The bearing should be a press fit onto the shaft.  Very light sanding of
the shaft with 600 grit sandpaper may be needed - just enough so that the
new bearing can be pressed on.  Or, gently tap the center race with hammer
(protected with a block of wood).  Make sure that the bearing is snug when
mounted so that the outer race cannot rotate - use layers of thin heat
resistant plastic if needed to assure a tight fit (the old sleeve bearing
was keyed but your new ball bearing probably won't have this feature).

These drills now run as smoothly as Sears' much more expensive models.

  8.10) Cordless drills

Cordless drills use a permanent magnet DC motor operating off of a NiCd
(usually) battery pack.  Manufacturers make a big deal out of the voltage
of the pack - 6, 7.2, 9.6, 12, 14, 18, etc. - but this really isn't a sure
measure of power and time between charges as a motor can be designed for any
reasonable voltage.  A gear reducer follows the motor driving a chuck for
holding the drill or screwdriver bit, or attachment.  These are most often
have a single or two speeds with reverse.

In addition to the problems listed in the section: "AC line powered drills",
these are also subject to all the maladies of battery operated appliances.
Cordless tools are particularly vulnerable to battery failure since they
are often use rapid charge (high current) techniques.

* Bad NiCd batteries - reduced capacity or shorted cells.  In most cases,
  a new pack will be required.

* Bad power/speed selection/reversing switch.  Replace.

* Bad motor.  These are usually permanent magnet brushed type motors.
  Worn brushes and bearings are common problems.  In addition, a partially
  shorted motor due to commutator contamination is also possible - see the
  sections on PM DC motors.  Disassembly, cleaning, and lubrication may be

  8.11) Other direct drive tools

* Rotary (Moto) tools - high speed compact universal or PM motors with a
  variety of chucks and adapters for holding tiny bits, grinding stones,
  cutters, etc.

* Routers, biscuit cutters - high speed (30,000 RPM typical) universal
  motor with a 1/4" (fixed size, router) chuck for common router bits.

  Ball bearings are used which have long life but are probably replaceable
  if they fail (noisy, excessive runout, etc.).

  The plug, cord, trigger, and interlock switches are prone to problems and
  should be checked if the tool doesn't run at all.

* String trimmers - universal motor on long handle with trigger control.
  Check for a bad cord, switch, and dirt in the motor if the unit appears
  dead.  The motor brushes could also be worn or not seating properly.

  8.12) Saber saws, reciprocating saws

These use a universal motor which drives a gear reducer and reciprocating
mechanism.  Better models have a variable speed control so that the sawing
rate can be optimized to the work.  All but the most inexpensive allow the
head to be rotated or rotate automatically based on feed direction adding
a bit of complexity.

A reciprocating saw is very similar but uses a much larger motor and beefier

In addition to motor problems, there can be problems with damage, dirt, or
need for lubrication of the reciprocating mechanism.

  8.13) Electric chain saws

WARNING: Read and follow all safety instructions using any type of chain saw.

These have a high power universal motor and gear reducer.  Most have the
motor mounted transversely with normal pinion type gears driving the
chain sprocket.  A few models have the motor mounted along the axis of
the saw - I consider this less desirable as the gyroscopic character of
the rotating motor armature may tend to twist the saw as it is tilted
into the work.

Inexpensive designs suffer from worn (plain) bearings, particularly at the
end of the motor opposite the chain since this is exposed to the elements.
Normal maintenance should probably include cleaning and oiling of this
bearing.  A loud chattering or squealing with loss of speed and power is an
indication of a worn and/or dry bearing  Replacement with a suitable ball
bearing is also a possibility (see the section: "Upgrading the bearings on a Craftsman drill" since the approach is identical.

Keep the chain sharp.  This is both for cutting efficiency and safety.  A
dull chain will force you to exert more pressure than necessary increasing
the chance of accidents.  Chains can be sharpened by hand using a special
round file and guide or an electric drill attachment.  Alternatively, shops
dealing in chain saws will usually have an inexpensive chain sharpening
service which is well worth the cost if you are not equipped or not inclined
to do it yourself.

One key to long blade and bar life is the liberal use of the recommended
chain oil.  Inexpensive models may have a manual oiler requiring constant
attention but automatic oilers are common.  These are probably better - if
they work.  Make sure the oil passages are clear.

The chain tension should be checked regularly - the chain should be free to
move but not so loose that it can be pulled out of its track on the bar.  This
will need to snugged up from time-to-time by loosening the bar fastening nuts,
turning the adjustment screw, then retightening the nuts securely.

There may be a slip clutch on the drive sprocket to protect the motor if the
chain gets stuck in a log.  After a while, this may loosen resulting in
excessive slippage or the chain stopping even under normal conditions.  The
slip clutch can generally be tightened with a screwdriver or wrench.

  8.14) Circular saws, miter, and cutoff saws

These have a high power universal motor either directly driving the blade
or driving a gear reducer (high torque/large blade variety).

Miter and cutoff saws are similar but are mounted on a tilting mechanism
with accurate alignment guides (laser lights in the most expensive!).

  8.15) Grinding wheels

A dual shaft induction motor drives rotating grinding stones (or other tools
like wire brushes).  Most common are fixed speed - usually around 3450 RPM
but variable speed operation is highly desirable to avoid overheating of
tempered metal during sharpening.  All but the most inexpensive use sealed
ball bearings requiring no routine maintenance.

Small light duty grinders may be 1/4 HP or less.  However, this is adequate
for many home uses.

Wet wheels may run at much slower speeds to keep heat to a minimum.  Being
in close proximity to water may in itself create problems.

  8.16) Polishers, rotary sanders

A gear reduced universal motor drives a rubber (usually) mounting plate
to which a sanding disk or polishing pad is attached.

Due to the nature of their use, sanders in particular may accumulate a lot
of dust and require frequent cleaning and lubrication.

  8.17) Orbital sanders and polishers

In addition to the usual universal motor and its bearings, the orbital
mechanism may require cleaning and greasing periodically.

  8.18) Belt sanders, power planers

A typical portable belt sander uses a gear or belt reduced universal motor
driving one of the rollers that the sanding belt rotates on under tension.
In decent quality tools, these should use ball or roller bearings which require
little attention.

A power planer is similar in many ways but the motor drives a set of cutters
rather than a sanding belt.

  8.19) Air compressors

A direct or belt drive induction motor (probably capacitor start)
powers a single or multiple cylinder piston type compressor.  Typical
continuous motor ratings are between 1/4 and 2 HP (for a 115 VAC line).
Over and under pressure switches are used to maintain the pressure in
an attached storage tank within useful - and safe - limits.  Most will
include an unloading valve to remove pressure on the pistons when the
compressor stops so that it can be easily restarted without damage to
the motor and without blowing fuses or tripping circuit breakers.

I much prefer a belt driven compressor to a direct drive unit.  One
reason is that a motor failure does not render the entire compressor
useless as any standard motor can be substituted.  The direct drive
motor may be a custom unit and locating a replacement cheaply may be

Drain the water that collects in the tank after each use.

Inspect the tank regularly for serious rust or corrosion which could result
in an explosion hazard.as well.

  8.20) Paint sprayers

Traditional air powered paint sprayers may simply be an attachment to an
air compressor or may be a self contained unit with the compressor built in.
Since the active material is paint which dries into a hard mass (what a
concept!), cleaning immediately after use is essential.  Otherwise, strong
solvents will be needed to resurrect a congealed mess - check your user's
manual for acceptable deadly chemicals.

Portable airless paint sprayers use a solenoid-piston mechanism inside the
spray head itself.  There is little to go wrong electrically other than the
trigger switch as long as it is cleaned after use.

Professional airless paint sprayers use a hydraulic pump to force the
paint through a narrow orifice at extremely high pressure like 1000 psi.

With all types, follow the manufacturer's recommendations as to type and
thickness of paint as well as the care and maintenance before and after use
and for storage.

Warning: high performance paint sprayers in particular may be a safety
hazard should you put your finger close to the output orifice accidentally.
The pressures involved could be sufficient to inject paint - and anything
else in the stream - through the skin resulting in serious infection or worse.

  8.21) Heat guns

These are similar to high performance hair dryers and subject to the same
problems - bad cord or switch, open heating element, defective thermostats,
universal motor problems, and just plain dirt and dust buildup.

  8.22) Paint strippers

These are just a high power heating element attached to a cord.  If there
is no heat, check for a bad plug, cord, or open element with your multimeter.

  8.23) Soldering irons

Simple pencil irons use an enclosed heating element is attached to the
'business' end in some manner - screw thread, set screw, clamping ring,
etc.  Failure to heat may be due to a bad plug, cord, bad connections,
or defective element.

Some types package the heating element and replaceable tip in a separate
screw-in assembly.  These are easily interchangeable to select the
appropriate wattage for the job.  Damage is possible to their ceramic
insulator should one be dropped or just from constant use.

High quality temperature controlled soldering stations incorporate some
type of thermostatic control - possibly even with a digital readout.

  8.24) Soldering guns

The common Weller Dual Heat soldering gun is a simple transformer with the
tapped primary winding in the bulk of the case and a single turn secondary
capable of 100 or more amps at around 1.5 V.  The soldering element is simply
a piece of copper (possible with a shaped tip) which is heated due to the high
current passing through it even though it is made mostly of copper.  The
'headlight(s)' (flashlight bulbs) operate off of a winding on the transformer
as well.

Possible problems include:

* No response to trigger - bad cord, bad switch, open transformer primary.

* Low or high (dual heat models) does not work - bad switch, bad transformer

* Lack of sufficient heat - bad connections where soldering element mounts.
  clean and/or tighten.  Tin the tip if needed (not permanently tinned).
  Use the high setting (dual heat models).

* Tip too hot - use the lower setting (if dual heat).  Do not keep the trigger
  depressed for more than 30 seconds or so at a time.  Manually pulse width
  modulate the power level.

* Entire unit overheats - this could be a shorted winding in the transformer
  but more likely is that you are simply not giving it a chance to cool.  It
  is not designed for continuous operation - something like 2 minutes on, 5
  minutes off, is usually recommended.

* No light - bad bulbs, bad connections, bad winding (unlikely).

Note: a soldering gun is not a precision instrument and should not be used
for fine electronics work - you will ruin ICs and printed circuit boards.
(However, I have heard of someone replacing an MC68000 microprocessor (64 pin
DIP) successfully with a large Weller soldering gun!)

  8.25) Wet-dry vacs, yard blowers/vacs

A powerful universal motor driving a centrifugal blower is all there is
in this equipment.  Unfortunately, many common models use cheaply made
motors which may fail simply due to use or from the dust and proximity
to liquids.  The blower sucks air and whatever else into the holding tank.
A filter is supposed to prevent anything from getting through.  The motor
itself should be sealed against direct contact with the dust/liquid section
of the machine.

Problems occur with bad cords, switch, motor brushes, bearings, or a
burnt out motor from excessive use under adverse conditions.

As with inexpensive electric drills, sleeve bearings (usually, the top
bearing which is exposed somewhat) in the motor can become worn or dry.
Replacing with a ball bearing is a worthwhile - but rather involved -
undertaking if this happens.  See the section: "Upgrading the bearings on a Craftsman drill" as the technique is similar (once you gain access -
not usually a 10 minute job).

  8.26) Hedge trimmers

A gear reduced universal motor drives a reciprocating mechanism not too
dissimilar to a saber saw.  In addition to the usual motor/electrical
problems, lubrication may be needed periodically.  Should you accidentally
try to trim a steel fence instead of a bush, damage to one or more teeth
may occur.  In this case, light filing may be needed to remove nicks and

Of course, you probably will not get away without cutting the power cord
a couple of times as well!  See the sections on power cords.  One way to
avoid the humiliation (other than being half awake) is to wrap a cord
protector around the first 2 or 3 feet of cord at the tool.  This will
make the cord larger in diameter than the inter-tooth spacing preventing
accidental 'chewups'.

  8.27) Electric lawn mowers

A large universal or permanent magnet DC motor drives one or two sets of
rotating blades.  A load or dead short may be thrown across the motor to
act as a dynamic brake when stopping.  As usual, when the mower does not
operate, check for bad plug, cord, switch, brushes, dirt, etc.  See the
sections on motors.

Chapter 9) AC Adapters and Transformers

  9.1) AC adapter basics

It seems that the world now revolves around AC Adapters or 'Wall Warts'
as they tend to be called.  There are several basic types.  Despite the
fact that the plugs to the equipment may be identical THESE CAN GENERALLY
NOT BE INTERCHANGED.  The type (AC or DC), voltage, current capacity, and
polarity are all critical to proper operation of the equipment. Use of an 
improper adapter or even just reverse polarity can permanently damage or
destroy the device.  Most equipment is protected against stupidity to a
greater or lessor degree but don't count on it.

The most common problems are due to failure of the output cable due to
flexing at either the adapter or output plug end.  See section below on
repair procedure.

1. AC Transformer.  All wall warts are often called transformers.  However,
   only if the output is stated to be 'AC' is the device simply a transformer.
   These typically put out anywhere from 3 to 20 VAC or more at 50 mA to
   3 A or more.  The most common range from 6-15 VAC at less than an Amp.
   Typically, the regulation is very poor so that an adapter rated at 12 VAC
   will typically put out 14 VAC with no load and drop to less than 12 VAC
   at rated load.  To gain agency approval, these need to be protected 
   internally so that there is no fire hazard even if the output is shorted.
   There may be a fuse or thermal fuse internally located (and inaccessible).

   If the output tested inside the adapter (assuming that you can get it
   open without total destruction - it is secured with screws and is
   not glued or you are skilled with a hacksaw - measures 0 or very low with no
   load but plugged into a live outlet, either the transformer has failed or
   the internal fuse had blown.  In either case, it is probably easier to
   just buy a new adapter but sometimes these can be repaired.  Occasionally,
   it will be as simple as a bad connection inside the adapter.  Check the
   fine wires connected to the AC plug as well as the output connections.
   There may be a thermal fuse buried under the outer layers of the
   transformer which may have blown.  These can be replaced but locating
   one may prove quite a challenge.

2. DC Power Pack. In addition to a step down transformer, these include at
   the very least a rectifier and filter capacitor.  There may be additional
   regulation but most often there is none.  Thus, while the output is DC,
   the powered equipment will almost always include an electronic regulation.

   As above, you may find bad connections or a blown fuse or thermal fuse
   inside the adapter but the most common problems are with the cable.

3. Switching Power Supply.  These are complete low power AC-DC converters
   using a high frequency inverter.  Most common applications are laptop
   computers and camcorders.  The output(s) will be fairly well regulated
   and these will often accept universal power - 90-250 V AC or DC.

   Again, cable problems predominate but failures of the switching power
   supply components are also possible.  If the output is dead and you have
   eliminated the cable as a possible problem or the output is cycling on
   and off at approximately a 1 second rate, then some part of the switching
   power supply may be bad.  In the first case, it could be a blown fuse,
   bad startup resistor, shorted/open semiconductors, bad controller,
   or other components.  If the output is cycling, it could be a shorted
   diode or capacitor, or a bad controller.  See the "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies" for more
   info, especially on safety while servicing these units.

  9.2) AC adapter testing

AC adapters that are not the switching type (1 and 2 above) can easily
be tested with a VOM or DMM.  The voltage you measure (AC or DC) will
probably be 10-25% higher than the label specification.  If you get no
reading, wiggle, squeeze, squish, and otherwise abuse the cord both at
the wall wart end and at the device end.  You may be able to get it to
make momentary contact and confirm that the adapter itself is functioning.

The most common problem is one or both conductors breaking internally
at one of the ends due to continuous bending and stretching.

Make sure the outlet is live - try a lamp.

Make sure any voltage selector switch is set to the correct position.
Move it back and forth a couple of times to make sure the contacts are clean.

If the voltage readings check out for now, then wiggle the cord as above in
any case to make sure the internal wiring is intact - it may be intermittent.

Although it is possible for the adapter to fail in peculiar ways, a
satisfactory voltage test should indicate that the adapter is functioning

  9.3) Pocket wall adapter tester/polarity checker

This handy low cost device can be built into an old ball point pen case or
something similar to provide a convenient indication of wall adapter type,
operation, and polarity:

            Probe(+) o-----/\/\-----+----|>|----+---o Probe(-)
                         1K, 1/2 W  | Green LED |
                                       Red LED

* The green LED will light up if the polarity of an adapter with a DC output
  agrees with the probe markings.

* The red LED will light up if the polarity of an adapter with a DC output is
  opposite of the probe markings.

* Both LEDs will light up if your adapter puts out AC rather than DC.

* The LED brightness can provide a rough indication of the output voltage.

The operating range is about 3 to 20 V AC or DC.

  9.4) AC adapter repair

Although the cost of a new adapter is usually modest, repair is often
so easy that it makes sense in any case.

The most common problem (and the only one we will deal with here) is the
case of a broken wire internal to the cable at either the wall wart or
device end due to excessive flexing of the cable.

Usually, the point of the break is just at the end of the rubber cable
guard.  If you flex the cable, you will probably see that it bends more easily
here than elsewhere due to the broken inner conductor.  If you are reasonably
dextrous, you can cut the cable at this point, strip the wires back far
enough to get to the good copper, and solder the ends together.  Insulate
completely with several layers of electrical tape.  Make sure you do not
interchange the two wires for DC output adapters!  (They are usually marked
somehow either with a stripe on the insulator, a thread inside with one
of the conductors, or copper and silver colored conductors.  Before you
cut, make a note of the proper hookup just to be sure.  Verify polarity
after the repair with a voltmeter.

The same procedure can be followed if the break is at the device plug end
but you may be able to buy a replacement plug which has solder or screw
terminals rather than attempting to salvage the old one.

Once the repair is complete, test for correct voltage and polarity before
connecting the powered equipment.

This repair may not be pretty, but it will work fine, is safe, and will
last a long time if done carefully.

If the adapter can be opened - it is assembled with screws rather than
being glued together - then you can run the good part of the cable inside
and solder directly to the internal terminals.  Again, verify the polarity
before you plug in your expensive equipment.

Warning:  If this is a switching power supply type of adapter, there are
dangerous voltages present inside in addition to the actual line connections.
Do not touch any parts of the internal circuitry when plugged in and make
sure the large filter capacitor is discharged (test with a voltmeter)
before touching or doing any work on the circuit board.  For more info on
switching power supply repair, refer to the document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies".

If it is a normal adapter, then the only danger when open are direct
connections to the AC plug.  Stay clear when it is plugged in.

  9.5) AC adapter substitution and equipment damage

Those voltage and current ratings are there for a reason.  You may get
away with a lower voltage or current adapter without permanent damage but
using a higher voltage adapter is playing Russian Roulette.  Even using
an adapter from a different device - even with similar ratings, may
be risky because there is no real standard.  A 12 V adapter from one
manufacturer may put out 12 V at all times whereas one from another
manufacturer may put out 20 V or more when unloaded.

A variety of types of protection are often incorporated into adapter
powered equipment.  Sometimes these actually will save the day.
Unfortunately, designers cannot anticipate all the creative techniques
people use to prove they really do not have a clue of what they are doing.

The worst seems to be where an attempt is made to operate portable devices
off of an automotive electrical system.  Fireworks are often the result,
see below and the section on: "Automotive power".

If you tried an incorrect adapter and the device now does not work there
are several possibilities (assuming the adapter survived and this is not
the problem):

1. An internal fuse blew.  This would be the easiest to repair.

2. A protection diode sacrificed itself.  This is usually reverse biased
   across the input and is supposed to short out the adapter if the
   polarity is reversed.  However, it may have failed shorted particularly
   if you used a high current adapter (or automotive power).

3. Some really expensive hard to obtain parts blew up.  Unfortunately,
   this outcome is all too common.

Some devices are designed in such a way that they will survive almost anything.
A series diode would protect against reverse polarity.  Alternatively, a large
parallel diode with upstream current limiting resistor or PTC thermistor, and
fuses, fusable resistors, or IC protectors would cut off current before the
parallel diode or circuit board traces have time to vaporize.  A crowbar
circuit (zener to trigger an SCR) could be used to protect against reasonable

I inherited a Sony Discman from a guy who thought he would save a few bucks and
make an adapter cord to use it in his car.  Not only was the 12-15 volts
from the car battery too high but he got it backwards!  Blew the DC-DC
converter transistor in two despite the built in reverse voltage protection
and fried the microcontroller.  Needless to say, the player was a loss but the
cigarette lighter fuse was happy as a clam!

Moral: those voltage, current, and polarity ratings marked on portable
equipment are there for a reason.  Voltage rating should not be exceeded,
though using a slightly lower voltage adapter will probably cause no harm
though performance may suffer.  The current rating of the adapter should
be at least equal to the printed rating.  The polarity, of course, must be
correct.  If connected backwards with a current limited adapter, there may be
no immediate damage depending on the design of the protective circuits.  But
don't take chances - double check that the polarities match - with a voltmeter
if necessary - before you plug it in!  Note that even some identically marked
adapters put out widely different open circuit voltages.  If the unloaded
voltage reading is more than 25-30% higher than the marked value, I would
be cautious about using the adapter without confirmation that it is acceptable
for your equipment.  Needless to say, if you experience any strange or
unexpected behavior with a new adapter, if any part gets unusually warm, or if
there is any unusual odor, unplug it immediately and attempt to identify the
cause of the problem.

  9.6) Replacing batteries with an AC adapter

While most appliances that run off of internal batteries also include a socket
for an wall adapter, this is not always the case.  Just because there is no
hole to plug one in doesn't necessarily mean that you cannot use one.

The type we are considering in this discussion are plug-in wall adapter that
output a DC voltage (not AC transformers).  This would be stated on the

The first major consideration is voltage.  This needs to be matched to the
needs of the equipment.  However, what you provide may also need to be well
regulated for several reasons as the manufacturer may have saved on the cost
of the circuitry by assuming the use of batteries:

* The maximum voltage supplied by a battery is well defined.  For example,
  4 AA cells provide just over 6 V when new.  The design of the device may
  assume that this voltage is never exceeded and include no internal regulator.
  Overheating or failure may result immediately or down the road with a wall
  adapter which supplies more voltage than its nameplate rating (as most do
  especially when lightly loaded).

* Most wall adapters do not include much filtering.  With audio equipment,
  this may mean that there will be unacceptable levels of hum if used direct.
  There are exceptions.  However, there is no way of telling without actually
  testing the adapter under load.

* The load on the power source (batteries or adapter) may vary quite a bit
  depending on what the device is doing.  Fresh batteries can provide quite
  a bit of current without their voltage drooping that much.  This is not
  always the case with wall adapters and the performance of the equipment
  may suffer.

Thus, the typical universal adapter found at Radio Shack and others may not
work satisfactorily.  No-load voltage can be much higher than the voltage at
full load - which in itself may be greater than the marked voltage.  Adding
an external regulator to a somewhat higher voltage wall adapter is best.  See
the section: "Adding an IC regulator to a wall adapter or battery".

The other major consideration is current.  The rating of the was adapter must
be at least equal to the *maximum