Subject: cellular (870-890 MHz) and low band (51-88 MHz) restoration for PRO-43

From: (A. Ray Miller)
Summary: cellular (870-890 MHz) and low band (51-88 MHz) restoration for PRO-43

A few people have mentioned the cellular mod for the PRO-43; it turns out
you should not remove but MOVE the diode.  Doing so allows cellular coverage as
well as low band (up to 88 MHz) coverage.

Acknowledgments to Grove Enterprises; this information came from them.
They are selling the PRO-43 for $300 which is $50 less than Radio Shack.
I have no connection with them other than as a satisfied customer.

	Cellular Frequency Restoration and Low Band Expansion

Note: It is not lawful to monitor cellular or conventional mobile telephone

The following procedure requires familiarity with microcircuit soldering and
will violate your warranty.  Grove Enterprises assumes no liability resulting
from its attempt, nor will accept the modified scanner for return under any

TOOLS NEEDED: Fine point, low power soldering pencil; solder wick or a
desoldering tool; pointed awl, hemostats or pointed tweezers; small Philips
screwdriver; solder.

1) Remove the battery, antenna and back cover (held in place by four screws).

2) Remove the six screws holding the top circuit board in place.  Carefully
unsolder the two antenna connections from the board.  Bend the antenna ground
tab fully up from the board.  Carefully lift the board, unplugging the black
connector at its base, and lay the board out of the way on its bundle of
colored wires.

3) Remove the two screws from the next board and lift it, carefully unplugging
the white connector at the bottom of the board.  Lift it up and lay it aside on
its brown wire (which can be unplugged if necessary).

4) Unsolder and remove the metal shield from the final board, revealing the
microprocessor; note the row of diodes labeled D1-D5 above it.  Only diodes
D1, D2, and D4 are present.  NOTE THE DIRECTION OF THE DIODE.
Assisted by a pointed tool, unsolder and remove D4, the lone diode (this 
restores cellular frequencies which will be searched in 30 kHz steps).

5) Resolder the removed diode carefully into position D3 to extend low band
coverage to 88 MHz.

6) Reassemble the boards, paying particular attention to the alignment of the
plugs.  Test the radio by entering any frequency between 870 and 890 MHz
(cellular) and 51-88 MHz (low band).  Performace above 50 MHz drops off rapidly 
as the tuned circuits are optimized for 30-50 MHz.
A. Ray Miller |


Subject: Improved audio for the PRO-43 portable scanner
From: (Bob Parnass, AJ9S)
Date: Wed, 2 Dec 1992 01:15:35 GMT


		      by Bob Parnass, AJ9S

     The Radio Shack PRO-43 scanner audio is too bassy.1 The
     lack of treble makes it difficult to hear the PRO-43 in
     noisy situations, especially while	listening in  a	 car
     or	 truck.	  Louis	Shirley	sent me	a schematic and	sug-
     gested I remove C341, a tiny 0.015	 ufd  surface  mount

     I'm glad to report	that  removing	C341  made  a  great
     improvement.   The	 audio	is  now	much "crisper,"	more
     like the Uniden 200xlt, although  still  not  quite  as
     loud.   Turning  the  volume control up still overloads
     the PRO-43's small, internal speaker, but there's	less
     need to do	that once C341 is removed.

     The PRO-43	contains 3 printed circuit boards,  and	 the
     middle  (second)  board  contains	the audio circuitry.
     Finding C341 is difficult,	as it is neither marked	with
     a	value nor a component designation.  It is located on
     the foil side of the  middle  board,  under  IC304,  an
     LM386 amplifier IC.  C341 is in parallel with, and	phy-
     sically next to, R350 (33,000 ohm).  R350	is  slightly
     larger than C341 and is marked 333.  Both R350 and	C341
     are connected between pin 2 of the	LM386 and ground.

		A Note About 50-88 MHz Reception

     Now that I	have a schematic, I see	 that  the  European
     version  of  the PRO-43 has different coils and capaci-
     tors in the low (mid)  band  front	 end  filter.	That
     explains why the 75 MHz sensitivity isn't stellar after
     adding diode D3 to	enable 30-88 MHz coverage.

 1. See	"PRO-43	Product	Review," by Bob	Parnass, AJ9S, in
    the	November 1992 RCMA Journal.
Bob Parnass, AJ9S  -  AT&T Bell Labs  - - (708)979-5414