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.



Disclaimers: Be sure to have the proper permits for out of band operations.

And, do this mod at your own risk!  WA2ISE



73s

3100 Ocean Park Blvd.   (213) 450-9111, ext. 2973 +-------------------------+

Santa Monica, CA  90405 {csun,philabs,randvax,trwrb}!ttidca!ttidcb!sorgatz **




SOURCE: The QRZ Windows Ham Radio CDROM