ICU2AT.3

Date: 9 Oct 89 13:37:06 GMT
Subject: Extended xmit mod for the Icom IC-u2AT handheld

Extended TX mod for the Icom IC-u2AT

This mod will extend the transmit range of the u2AT from 139 Mhz to
about 161 Mhz (maybe further if you adjust the PLL).  You'll be working
with a surface mount PCB, so you will need a fine point soldering iron
and a very steady hand.  And you will need one diode, like a 1N914, or
a tinyier one if you can get it.

You must have the service manual to help you identify where the new diode is
to go.  Review all the below with the manual before you reach for your
screwdriver and soldering iron!

>remove the battery pack.
>remove 4 screws that hold the sliding guide that the battery pack mounts on.
This is the piece of metal that frames the PL tone switches.
>remove the sliding guide. Be careful that you don't lose the battery release
button.
>there's a screw on the left side of the HT just below the light switch.
Remove it.
>CAREFULLY pry the front panel up.  There's speaker wires AND a flexable lead
that goes to the front panel.
>There's a shielded PCB that these leads run to.  Carefully pry this up.  It
will then fold down.  There's several flexable leads at the bottom.
>You should see the CPU now.
With the manual, locate where D113, D119, Q131 are.
>Where the new diode goes is not marked in the diagram of the CPU PCB.  Locate
the anodes of D119.  This land connects to pin 27 of the CPU chip ic101.
Locate the cathode of D113.  This land connects to pin 20 of the CPU chip.
These diodes are SMDs, and do not look like what you'd expect diodes to look
like.
>In the area between Q131, D119, D113, and the CPU chip, you should see
a set of 3 solder pads that form a trianglular pattern that would accept a 3
legged SMD, like the neighboring diodes and transistors.  One of these pads
connects to the anodes of D119.  The new diode's anode goes to this pad.
Another pad connects to the cathode of D113.  The cathode of the new diode
goes here.  This means that the new diode cathode will connect to pin 20 of
the CPU, and that the anode will connect to  pin 27 of the CPU.
>Carefully prepare the diode leads to line up with the proper pads, and take
care that when you solder it on, you don't short to something.  Also, take
anti-static precautions.  I used a bit of double-sticky-foam tape to hold the
diode in place when I soldered it.  And I left the tape to help keep it in
place after I was done.  Be sure that you will be able to replace the PCB you
pried up, without it touching the diode.
>Reassemble the rig.
>Do a CPU reset.  That is: Turn the power on while holding the light switch
down.
>You should be able to xmit between 139 to about 160 Mhz.  You could tweak the
PLL to extend it further, but I didn't do this.  The xmit power will be lower
on the higher freqs.