From: gettys@yacht.enet.dec.com (Bob Gettys)
Subject: Icom IC-4SAT  xtnded transmit mod - how to
Date: 22 Jul 91 20:37:58 GMT
Organization: Digital Equipment Corporation
Lines: 71


	Ok, I recently asked the net for mods to expand the transmit
	frequency coverage of the Icom IC-4SAT so that I could access
	the rest (or at least more ) of the 440 ham band below 440mhz.
	Well, the net didn't come through but a local ham made a
	suggestion to me that I followed up on. I mentioned that I had
a mod (see attached message below) for the IC2SAT to expand its
transmit range. He suggested that I look at doing the same mod (I know
- it sounds crazy). Since I have the tech manual for both units







oked at the 2S manual to see what the mod was doing. I then looked at
the 4S manual to see if things were similiar. To my suprise (although
in retrospect I'm not suprised, just suprised that I didn't think of
it) the microprocessor section is IDENTICAL wi th only the
initialization matrix of diodes being different between the 2S and the
4S. Even the part numbers of the micro were the same (led me to believe
that the code is the same in both). So I tried the mod explained
below.

	Bottom line - it worked!!  I get about 30 mhz of lock range
	from about 435mhz to 465mhz. My next step will be to look at
	retuning the vco to move it down in the ham band more.

	/s/	Bob Gettys N1BRM

Thanks to David Thomas whose 2SAT mod is attached below for posting it last fall.

------------------------------------------------

From: dt@yenta.alb.nm.us (David B. Thomas)

=====
I have just discovered a way to turn off the policeman in the 2sat that stops
the transmitter from operating outside of 140-150 Mhz.  The only limitation is
now transmit VCO lock range, which, out of the box, is about 137 to 162 mc.
I'm sure by tuning a slug one could raise or lower this coverage "window".

To do the mod, you'll need a soldering iron with a VERY fine tip, some fine
solder, some small screwdrivers, a 1N914 diode (or other small silicon diode),
some fine (wire wrap) wire, and (probably) a magnifying glass!

Follow the directions on page 34 of the instruction booklet to take the unit
apart.  This allows the front panel to be removed from the radio.  No further
disassembly is required, or recommended.  Watch out for the little springy-
dingy that locks the battery in place on the radio (the book so cautions).

Looking at the inside of the front panel, you should easily spot the CPU chip.
(it is even shown as a square symbol in the picture on page 34.)  Just to the
right of the bottom right portion of the CPU is a teeny three legged device,
exactly to the right of which are three solder terminals where another such
device could fit.  Here's some ascii art:


  ||||||||||||||||||||
 |--------------------|
=|                    |=	vacant diode chip pads
=|                    |=                    |
=|                    |=		    |
=|     C P U          |=                    /
=|                    |=   ---XX---     XX
=|                    |=   |      |
=|                    |=   -XX--XX-   XX  XX  <=== point A
=|                    |=
 |--------------------|      /		 ---XX---  <=== point K
  ||||||||||||||||||||	     |		 |      |
			     |		 -XX--XX-
			     |
			diode chips-----/


The scaling is pretty bad, but it's pretty easy to find the three unused pads,
then look left for one diode chip, then down and to the right for the other,
as shown.

To implement the mod, it is necessary to install a diode of your own from
point A (anode) to point K (cathode) in the diagram above.  These points are
EXTREMELY close together, and the board is delicate, so I recommend the
following:

Take a 1N914 diode and cut the leads to 1/8 inch or less, then solder fine
(26 ga. or thinner) wires of different colors to the leads, noting which is
the cathode and which is the anode.  Now put a piece of heat shrink or tape
over the diode so that only the little wires escape.  This assembly can now
be safely soldered into the circuit, and the unit carefully reassembled.

Reset the CPU (see inside font cover of manual) and you're on the air!

						little david

 
Copied from the QRZ! Windows Ham Radio CDROM