Modifications to Radio Shack (Tandy) PRO-2004 Scanner
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These mods are extracts detailed in the following articles:
a) POPULAR COMMUNICATIONS AUG 87, PP 18-20
b) MONITORING TIMES OCT 87, P 53
c) MONITORING TIMES DEC 87, P 60
It is suggested that you obtain the back issues and read through the letters and articles. A subscription to the magazines is worthwhile as they supply a lot of interesting scanner information as well as useful frequency lists. Also Radio Shack sells a technical manual on all their electronic equipment, which contains maintenance and calibration procedures, as well as schematics.
Preliminaries:
First, treat the radio as if it were CMOS. That is make sure you take
precautions concerning static charges. Second, unplug the radio from the antenna and AC power. Remove batteries. Take the radio out of the case by removing the 4 screws on the back. Carefully invert the radio.
Locate a box-like sub-circuit. It's near the switch marked "restart".
The sub-circuit should be marked PC-3. Carefully pry off the cover of the metal box. Inside there will be a 64 pin dip IC. This is the radio CPU. Be careful not to touch or short out any leads on the chip.
1) Restoring 870MHz coverage.
   Near the chip there will be a row of diodes marked D502 to D515.
   If D513 is present, cut one lead, separate it so they will not         touch, and 870Mhz is restored. If D513 is not there and you still      do not have 870 coverage, then a little more work is in order.         Locate the 9 pin connector "CN501". Carefully remove it from the       sub-circuit.
   Remove the screws holding PC3 to the main chassis. Carefully invert
   the sub-circuit board (PC3). Locate the lone component on that side
   of the board. If it is a diode, as it should be, then cut one lead     and separate them as above. Reinstall the sub-circuit with the         screws on to the main chassis. Reconnect the 9 pin connector. Do       NOT put the cover back on just yet.
2) Increasing from 300 to 400 channels
   On the top of the sub-circuit board, locate the slot for D513.         Count backwards from there until you get to the space for D510.        Install a diode at D510 in the same polarity as the rest of the        diodes. You now have 400 channels instead of 300.
3) Increasing scanning speed to 20 channels per second
   Now install a diode at D514 and you have increased the scan speed      to 20 channels/sec from 16 ch/sec.
4) Improving squelch operation
   Carefully reassemble the metal box. Make sure everything else is as    it should  be. Invert the radio so it is right side up. Now, locate    a sub-circuit box  under the sloping front panel. It should have       many alignment holes in the top.  Pry the cover off very carefully.    Locate IC2 in the left side of the PC  board. It should be marked      IC10420. Locate R148, a 47K ohm resistor between pins 12 and 13.       Cut a lead of this resistor, But be sure to leave enough lead on       both sides of the cut to solder to. Patch in a 100K ohm resistor.      Make sure there are no solder balls or short  circuits. Now your       squelch will operate much better.

 Gene WA1UXA
 PS, install the metal cover and the radio back in the case.

Addresses:
Popular Communications
76 N Broadway
Hicksville, NY. 11801
Monitoring Times
140 Dog Branch Rd
P. O. Box 98
Brasstown, NC. 28902

PORTED AND REALIGNED FROM PC TO AMIGA FORMAT BY BOB G0LBQ - N6XDI.