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World of Ham Radio 1997
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WOHR97_AmSoft_(1997-02-01).iso
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icu2at_6.doc
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1997-02-01
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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 (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 scrwdriver 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 athode 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.
Disclaimers: Be sure to have the proper permits for out of band
operations. And, do this mod at your own risk! WA2ISE