From: horak@convex.com (David Horak)
Subject: Here are the PRO-34 MODS
Organization: CONVEX Computer Corporation, Richardson, Tx., USA
Date: Thu, 10 Sep 1992 13:20:50 GMT
X-Disclaimer: This message was written by a user at CONVEX Computer
              Corp. The opinions expressed are those of the user and
              not necessarily those of CONVEX.


I've had numerous requests for Pro34 mods, so here's my version.

Note: In the Pro37, the cell mod is essentially the same, but the part
you need to clip is D13.

*************************   Pro34 Mods   ******************************

Remove the four screws from the back of the unit, then remove the
batteries.  Gently remove the back cover from the unit.  You will need
to de-solder the antenna from the top board.  Then remove the nuts
holding the squelch and volume pots.  There may be a wire at the other
end of the top board to de-solder, which I think is mainly for
grounding purposes.  Then, there are four hex screws holding the top
board on. Remove these and carefully wiggle the top board loose from
the bottom.  I say wiggle because there is a multi pin connector to
unhook.  Once unplugged, slide it out horizontally so that the volume
and squelch pots slide out with the board. Then there are three screws
to remove to lift the metal shielding from the bottom board.  Once you
have the bottom board in plain view, you should see D9, D10, D11 and
D12 on one side of the board. Cut one lead of D11 and seperate the
leads so they dont touch. This removes D11 from the circuit and adds
the 800 mhz cellular phone bands to your scanner. It is a hassle to get
to D11, but the added frequencies are worth it in my opinion. Of
course, LISTENING TO CELLULAR PHONE CALLS IS ILLEGAL! There are other
mods that do various things to the diodes but these mods are of little
value. One, for instance, adds the 66-88 Mhz band but it also removes
the 30-54 Mhz band at the same time.  In addition, many units won't
even pick up anything in the 66-88 band without major realignment. I
know mine won't! There is one other mod that's worth doing. I can't
remember the part designation, but there is a ceramic 2 Mhz crystal on
the logic board (probably blue in color), near the main CPU  You can
replace it with a 3.4, 3.55 or similar value for increased scanning
speed. If you go over 4 Mhz, your CPU *may* not be able to maintain its
integrity. If you use a normal crystal, you'll have to bend the leads
over and lay the crystal flat over a nearby chip. It will fit though
and it works! Make sure the crystal leads and the crystal body are
insulated from touching any other circuits. If you use the two second
delay, it will be affected by the crystal. The delay time will be
reduced by increasing the crystal frequency. When you put the unit back
together, make sure the key lock switch is intact. Mine fell out and I
didn't notice it was missing until I had everything back together.
Also, don't get the antenna connection too awful hot. There is a
surface mount cap near the underside that will fall off if you apply
too much heat. This is the input cap from the antenna. You'll notice
decreased signal strength after you put it all together again. It can 
be a real bear trying to put surface mounted parts back on the board!!
Trust me ;-)

Have fun. If you really screw up your radio, it's NOT MY FAULT !!!!!!
David Horak N5OFQ
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