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From: sseeger@stellartec.com (Steven Seeger)
To: "'webmaster@qrz.com'" 
Subject: ICOM T81A Mod
Date: Wed, 23 Jun 1999 10:35:26 -0700

I'm not sure I'm sending this to the right person, but it'd be great to see 
it listed in the RADIO MODS section.

I've noticed you don't have any mods for the T81A quad bander from ICOM. I 
just wanted to say that after reading the other mods for various radios 
I've figured out the receive mod for this one. It seems to be a touch 
trickier. The radio must be powered off in VFO mode so that when you turn 
it on, it isn't in the memory channels. Hold down SQL and the MULTI button 
(you must hold down the button as you would confirming choices in the 
radio, ie not in any one diretion but all of them) and then viola, there's 
all the receive. Just wanted to share it with everyone. :)

-Steven
KF6WJH


Rob Neff (N7ORY) writes:


Removing the battery pack and two screws at the bottom. Remove the antenna and ring-nut, also remove knob. Lift the circuit out carefully.

Below LCD, right side of pcb, there will be 5 or 6 places for diodes. 1st and 5th diode installed from factory. To the right of small diodes, another set of larger diodes parallel to the row of smaller ones.. The layout looks like this..

[-]
[ ] ( )
[ ] ( )
[ ] ( )
[-]

They are labled (from top to bottom for the small diodes)
d55,d54,d57,d66,d61.. The larger ones are labled (top to bottom) d53,d52,d51.. 

To open TX, remove the diode from the 5th spot down in the row of small diodes (d61), and also remove the first of the larger diodes (the one at the top, d53). This mod does not require resetting the cpu.

New TX freq limits:
50.000 to 54.000 MHz
136.000 to 173.995 MHz
400.000 to 469.000 MHz
1.2 same

To open TX farther, remove the first smaller diode, d55. This appears to TX on 220. It does open up 5 meters however. It will TX above 54 Mhz. The first mod does NOT open 5 meters.

50.000 to 75.000 MHz
136.000 to 229.000 MHz 
400.000 to 599.995 MHz
1.2 same.

From: "Rob Neff" 
To: 
Subject: IC-T81A MARS/CAP MOD
Date: Wed, 18 Aug 1999 10:04:56 -0700

This is the complete mod. Please read completely.

Open the radio by removing the battery pack and the two screws at the
bottom, inside the back. Then remove the antenna and the ring-nut that
holds that in place, also remove the knob. Lift the circuit out of the
case carefully.

Looking at the front of the unit, cover off of course, just below the
LCD on the right side of the PCB there will be a series of 5 or 6 places
for diodes. On my unit, only the first and 5th diode are installed from
the factory. Just to the right of those diodes is another set of larger
diodes, three of them, in a row parallel to the row of smaller ones..
The larger diodes have 3 legs. The layout looks like this..

[-]
[ ]   (    )
[ ]   (    )
[ ]   (    )
[-]

They are labeled (from top to bottom for the small diodes)
d55,d54,d57,d66,d61..
The larger ones are labeled (top to bottom) d53,d52,d51..
The 6 legged diode to the right of the larger ones does not get messed
with! Its d58 BTW

Ok, now for the meat. To open TX on the T81, remove the diode from the
5th spot down in the row of small diodes (d61), and also remove the
first of the larger diodes (the one at the top, d53). This mod does not
require resetting the CPU.

New TX freq limits:
50.000 to 54.000 MHz TX
136.000 to 173.995 MHz TX FM
400.000 to 469.000 MHz TX
1240.000 to 1300.000 MHz TX

To open up TX farther, remove the first smaller diode, d55. This appears
to TX on 220. It also opens up 5 meters. It will TX above 54
MHz. The first mod does NOT open 5 meters. On my unit it will only go up to
63 MHz  before it unlocks though.

50.000 to 76.995 MHz TX
136.000 to 229.000 MHz TX
400.000 to 599.995 MHz TX
1.2 GHz stays the same.

Operate responsibly and never transmit out of band unless you are
licensed and the radio is type accepted for that frequency.

These diodes are VERY small and its very easy to accidentally bridge pads
with solder that shouldn't be. If you perform this mod you do so of your
own accord and with out warranty to its success. If you perform the mod
and your receive is very weak, or non existent, one of the lower solder
pads on the row of small diodes may be bridged. I had this happen to me
and I about died till I figured it out. USE A LOW WATTAGE, FINE TIPPED
SOLDERING IRON. !!!SAVE THE PARTS!!!


Date: Wed, 17 Jul 2002 16:06:46 -0500
From: George 
Subject: New Mod - Icom IC-T81A deviation adjustment

Hello.

I would like to submit a useful mod for the IC-T81A handheld.  This mod 
has text and a image to accompany it.  I will paste my text below, 
include it in an attached text file, and attach the image.  Enjoy.

Thanks!

George
KG4OZL
--------------


I've owned and handled several IC-T81A HTs and they were all WAY too 
loud - loud enough to knock me out of contact with repeaters and earn me 
numerous complaints of over-deviation.  Deviation on each was measured 
at over 6KHz.  Chances are, your IC-T81A does the same thing.

After receiving a service manual from Icom for the T81A, I was able to 
successfully adjust my radios to the manual-specified maximum of 4.5KHz. 
  Now, they sound great!

  Here is a page detailing the adjustments ( see ict81a.jpg ) - one 
  potentiometer for each band, plus one for DTMF / tone call.  Deviation 
  is lowered by turning the pots counterclockwise.  WARNING: Attempt this 
  mod at your own risk, and ONLY with the proper service gear to measure 
  deviation.

  To disassemble the radio, remove antenna, battery and knob.  Remove the 
  SMA jack nut, remove the two screws on the back of the radio, carefully 
  pull radio out of plastic shell.

  Enjoy

  George
  KG4OZL

  kg4ozl@mindstate.com

 

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