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REPAIR TIPS: BEARCAT SCANNER RADIOS
Copyright 1993 - 2001 by Bob Parnass, AJ9S
[NOTE: This article may not be reproduced in whole or in
part on CDROMS, in bulletin boards, networks, or
publications which charge for service without permission of
the author. It is posted twice monthly on the USENET
groups rec.radio.scanner, alt.radio.scanner,
sci.electronics.repair, and rec.radio.info. It is also
available electronically from the rec.radio.scanner ftp
archive on the official USENET FAQ library
ftp://rtfm.mit.edu/pub/usenet-by-group/.
The author writes a monthly "Scanner Equipment" column for
Monitoring Times magazine, published by Grove Enterprises
http://www.grove-ent.com but views expressed in this
article are his own.]
Introduction
The original Bearcat scanner line was manufactured by
Electra Company, a division of Masco Corp of Indiana. In
the mid 1980s, Uniden, a Japanese company, bought out the
Bearcat scanner line and Uniden's first Bearcat scanner was
the BC800XLT model.
Most of the models discussed in this article are
base/mobile units made by Electra during the 1970s and
1980s although some of the capacitor failures occur in the
Uniden BC800XLT, too.
Electra stamped all of its scanners with a manufacturing
date code on the rear of the cabinet. The code is comprised
of a single character (C = Cumberland, Indiana, P = Puerto
Rico), followed by four digits denoting year and week the
radio was built. For example, "P8422" denotes the radio was
made in the Puerto Rico factory during the 22nd week of
1984.
One way to roughly estimate a radio's age is to examine the
4 digit date codes often stamped on the integrated
circuits. The radio must have been made after the most
recent date stamp.
Schematics, Owner's Manuals, and Parts Available
The re-incorporated Electra Corporation sells crystals,
antennas, power cords, owner's manuals ($11 ea) for some
older (pre-Uniden) Bearcat scanners. Electra Corporation
is located at 11915 E. Washington St., Cumberland, IN
46229. Phone 317-894-3229, email: electra@tcon.net,
I cannot furnish schematics, manuals or parts. To order a
user manual for an Electra/Bearcat scanner from Uniden,
call (800)235-3874 extension 2553. You can also download
an electronic copy of the user manual for recent Bearcat
models from the Uniden web site:
http://www.uniden.com/docs/service/support.htm
Some schematic diagrams may be obtained from Uniden's parts
department, (800)297-1023. Uniden currently charges a flat
rate of $54 for scanner repairs. They will repair and
return "out of warranty" items without an estimate unless
the repair charges exceed the flat rate charges.
The phone number for repair is (800)297-1023, too. I
recommend you call repair before sending the broken
scanner. Items for repair via UPS (include receipt if
still under warranty) are usually sent to:
Uniden America Corp.
4700 Amon Carter Blvd.
P.O. Box 95002
Fort Worth, TX 76155
If Uniden doesn't have a schematic, try obtaining a
Photophacts from Howard Sams Publishing division of
Prentice-Hall at (800)428-7267, http://www.samswebsite.com
G & G Communications (telephone (716)768-8151) is a family
owned company which repairs scanners and stocks parts for
several older models, especially Electra/Bearcat and
Regency brands, but they don't sell manuals or schematics.
They are located at 7825 Black Street Rd., LeRoy, NY 14482.
(http://www.iinc.com/ggcomm/ or email ggcomm@iinc.com or
ggcomm@aol.com)
Multec Communications repairs several model Uniden
scanners, but not Electra models. (http://www.rfwiz.com or
email multeccomm@rfwiz.com)
Common Construction
Most of the classic, metal-cased Bearcat base/mobile models
were built using two printed circuit boards:
1. a "radio board" containing the synthesizer, RF, IF,
and audio stages, and
2. a "feature board" containing the microprocessor
controller and memory circuitry which gave each model
its own personality.
Although there are various vintage radios boards, they all
have similar circuitry.
Bad Solder Joints Common
Before addressing specific symptoms, circuit boards in the
malfunctioning scanner should be inspected for poor solder
joints.
The Electra/Bearcat BC350, BC300, BC250, BC220, BC20/20,
BC211, BC210, and BC210XL models were hand assembled, and
every one I've serviced had several connections that were
either soldered poorly, or not soldered at all.
Resoldering joints on the ribbon cable connecting the RF
and keyboard logic circuit boards in a BC250 attenuated the
microprocessor/synthesizer hash noise noticeably.
A Bearcat 20/20 was experiencing periodic loss of memory on
some, but not all channels. When the problem occurred, the
frequencies on some channels would be completely changed.
On other channels, the frequency would still be intact, but
the channel would be locked out, and the delay toggled from
"on" to "off". Some channels were not affected.
The 2 "AA" memory backup batteries, and their holder,
tested good. Much time was spent tracing logic, heating
and cooling components, and making voltage measurements.
One of the secondary leads from the power transformer was
connected to the main circuit board through a hole drilled
through foil traces on both the top and bottom sides of the
board. A close examination revealed that this lead had
been soldered only on the top of the board - the bottom
side had never been soldered.
Soldering the lead on both sides of the board solved the
memory loss problem.
Matt Roberds fixed a BC220 which experienced memory loss if
power was removed by resoldering the positive wire to 2-AA
battery holder.
As built, the BC220 logic board is grounded only through
its mounting screws. In the BC220, Matt recommends adding
real wire ground jumpers from the main board to the feature
(logic) board to fix grounding problems.
Symptom: Blank Display
The BC300 scanner, and several other Bearcat models, employ
a switching type power supply stage to generate plus and
minus voltages in excess of 20 volts DC. When this
switcher fails to function, the display goes blank, but the
squelch control appears to work, and white noise can be
heard in the speaker.
In almost a dozen of the BC300 and BC800XLT scanners I've
fixed, C98, a capacitor in series with the primary of the
switching transformer failed, causing the output of the
supply to drop below the level needed to power the display.
The switching transformer is mounted on the RF circuit
board, and is much, much smaller than the main power
transformer, which is usually fastened to the metal
chassis. See March 1996 Monitoring Times magazine for
BC800XLT capacitor locations and repair information.
The 22uF/16V capacitor used for C98 in early BC300s was
marginal, and was replaced with a 47uF/25V capacitor in
later units.
Jim Craig and Karl Klein repaired their BC210XWs by
replacing the 22uF/35V C98 capacitor.
Paul Grohe replaced a failed C98 with a low ESR (equivalent
series resistance), high frequency, switching regulator
grade capacitor, e.g. a Panasonic HF series capacitor. He
also recommends adding a 0.1 ceramic capacitor in parallel
with C98.
I replaced the 22 uF capacitor in the switching power
supply stage of a BC210XL which caused the same symptom.
Other capacitors in the switcher stage have failed. C114,
a 4.7 uF/35V tantalum capacitor failed in at least one
BC250, causing the display to blank.
A more sinister problem affects the switcher in earlier
models. The switching supply stage in the BC250 and
original BC210 is driven by a clock signal derived from a
custom Exar NC57902 divider integrated circuit (designated
IC6 in the BC250 scanner). I've seen this divider IC fail
in several BC250s, causing a blank display (except for a
decimal point in the BC250's rightmost digit). This custom
IC is no longer available from Uniden.
Failure of IC9, the 9 volt NJM78M09A regulator in a
BC800XLT is another cause of a blank display.
Symptom: Invalid Frequency Displayed
A common Bearcat 250 malady is manifested by an invalid
frequency displayed on the readout. This display is
temporarily "cured" by unplugging the AC line cord from the
wall, then replugging it. This condition is symptomatic of
a power supply problem in which Q204, a Texas Instruments
TIP-29 located on the feature circuit board, fails.
A Philips ECG291 will work as a substitute for the TIP-29.
Don't try a Radio Shack substitute, it hasn't worked. See
Martin Toomajian's article, "Bearcat 250 Erratic Display
Cure", in January 1987 Monitoring Times.
A similar problem in the Bearcat 20/20 was discussed
previously in the section on bad solder joints.
Matt Roberds repaired the Montgomery Wards version of a
BC220 and contributed these insights:
"I did add some heat-sinks, but you have to be careful what
you do with the TIP29 on the logic board. I added a long,
flat heatsink to it and immediately created a whine in the
audio. I didn't use an insulator, as this was a temporary
first-try. As far as I can tell, the heatsink was
radiating noise from the logic board into the front end on
the radio board, which ended up being just below the
heatsink. Bypassing the TIP29 (a voltage regulator) with
disc ceramics didn't work; using a smaller heatsink and an
insulator fixed the problem."
"There is also a 220 ohm 1/4 watt resistor on the logic
board. It feeds the TIP29 from the main +16v supply. It
looked a little crispy. I pulled one end and measured the
current through it and it was about 30-35 mA. This works
out to right at 0.2-0.25 watt dissipation. I didn't have a
higher-wattage resistor, so I substituted 2 470-ohm
resistors in parallel."
Symptom: Squelch Won't Eliminate White Noise
Most Uniden/Bearcat base/mobile scanners feature an AUTO
squelch position, actuated by rotating the squelch knob
fully counter clockwise. The BC350 used a separate
pushbutton switch for this purpose. These scanners use a
flimsy potentiometer (designated R81 in BC300s) internally
mounted on the RF circuit board, to set the level of signal
required to open the squelch when in the AUTO position.
This pot also has an effect on the squelch action in the
non-AUTO mode, and determines at which point the squelch
knob must be positioned in order to silence the radio.
Although the potentiometer is adjusted at the factory,
changes in component values due to aging often necessitate
readjustment of this internal pot. Misadjustment of this
pot has been the cause of "no squelch" complaints in two
BC300s and a BC250 I fixed.
Another squelch failure is due to a blown transistor that
acts as the electronic switch in the squelch circuit. I
replaced this transistor in only one BC300, so I don't know
if this is a common problem.
Symptom: Scanner Completely Dead
In Bearcat scanners using an internal power supply (e.g.,
BC350, BC250, etc.), the main power transformer is
connected directly to the AC line. Since the on/off switch
is on the secondary side of the transformer, current flows
in the primary as long as the AC line cord is plugged into
an active AC outlet. These transformers contain an
internal circuit breaker, not visible without unwinding
(destroying) the transformer. The internal breaker is
known to fail prematurely in a batch of Bearcat power
transformers.
If your scanner is completely dead, check the primary of
this transformer for an open circuit condition.
Symptom: Keyboard Bounce
After much use, the Chromerics keyboards in Bearcat
scanners start to wear out. The first sign of trouble is
usually keyboard bounce on the most frequently used key,
e.g., the MANUAL key. Replacement keyboards are usually
available from UNIDEN, but replacement requires dexterity,
as one must take care not to tear the flat, flexible strip
connecting the keyboard to the logic board.
Symptom: Keyboard Completely Unresponsive
The keyboard matrix is "scanned" by the microprocessor.
Another problem is when none of the keys seems to function;
the receiver just keeps scanning in spite of key
depressions. I found this condition in a BC210XL scanner
owned by a heavy smoker. Perhaps nicotine smoke was to
blame, as the resistance between two input port pins on the
microprocessor was down to about 1000 ohms, fooling the
microprocessor into believing that a key was stuck in the
"down" position. Scraping the circuit board between the
two pins with an X-Acto knife fixed the problem.
Uniden/Bearcat BC200XLT Portable
Loss of Audio and Dial Lamp
If you can program frequencies into your BC200XLT but there
is no audio and the green backlight no longer functions, a
tiny transistor may have failed.
Check for a defective PNP surface mount transistor, Q201
(2SB815B6-YDY). Q201 is used as a switch to furnish 8 VDC
to several stages of the BC200XLT. Its main purpose is to
switch off power hungry stages of the BC200XLT when the CPU
thinks the NiCd voltage has fallen below a threshhold.
That's an attempt to limit the current drain on weak NiCds
to avoid permanent damage.
Q201 is located on the foil side of the "Micom" board,
adjacent to the black multi-pin connector which mates the
Micom and main boards together.
Q201 can be destroyed by a few different causes, primarily,
by something in the scanner drawing too much current
through it. In one case, capacitor C36 shorted. It's a 220
uF 10v electrolytic, located on the component side of the
main board, connected from pin 8 of the audio IC (IC2
NJM386SL) to ground. Capacitor C55 shorted in another
BC200XLT. Gary Bean reports he substituted a 2SA1298 for
Q201 and it worked fine. In a pinch you bypass Q201 by
soldering a short piece of bare wire between the collector
and emitter, but you must first fix the component which
caused Q201 to fail.
BC9000XLT: Loss of Sensitivity
John Ward has fixed two BC9000XLTs which suffered from "low
sensitivity." He fixed the solder joint where the antenna
jack connects to the circuit board. In both cases the tab
from the board was on the opposite side of the jack from
where the little blob of solder applied at the factory was
located.
It was an intermittent problem that depended upon the
position of the antenna cable - if the weight of the cable
placed tension on the jack in one direction contact was
made and the radio worked fine. If the cable placed
tension on the jack in the opposite direction contact was
lost and so was reception. The gap was barely noticeable.
Other Problems
Complaints of low audio output and occasional microphonics
in three Uniden/Bearcat 800XLTs were caused by a bad 47 ufd
electrolytic capacitor in series between the external
speaker jack and audio amplifier.
Andy Domonkos reports he often uses a tape recorder
connected to a Uniden/Bearcat BC890XLT. RL-1, the carrier
activated relay inside the BC890XLT wore out. Andy found
the identical relay sold at Radio Shack (part #275-232) and
says the BC9000XLT uses the same relay, too.
Replacement Bulbs for BC760XLT
The Uniden BC760XLT's SCAN, MAN, PRI, and HOLD buttons are
illuminated by "grain of wheat" type incandescent bulbs.
Gary Saffer reports that the bulbs and buttons are located
on a small printed circuit board which sits behind the
radio's face plate. Gary unsoldered the burned out bulbs
in his radio and replaced them with 12 volt Radio Shack
bulbs (#272-1092c). They should last a long time when
powered by the 8 VDC supplied by the BC760XLT.
Open Resistor in BC140
Robert Casey fixed his deaf, 16 channel Bearcat BC140
scanner. A 10 ohm resistor had opened that fed a circuit
that generates 22V for the varactor diode tuner circuits.
Without the 22V, there was no tuning of the local
oscillator and front end, and no reception. What he did
was compare voltages to a second working BC140.
Sources for Replacement NiCd Battery Packs
Replacement NiCd battery packs and inserts for the
BC100XLT, BC200XLT, BC2500XLT, BC3000XLT, and other
scanners are available from Uniden. I've purchased them at
lower cost from:
1. Mr. NiCd - E. H. Yost and Company, 2211-D Parview
Rd., Middleton, WI 53562. tel. (608)831-3443. email
ehyost@midplains.net
2. Battery-Tech Central, 2818 Southland Street SW, Cedar
Rapids, IA 52404-4141. tel. (800)267-3087 or
(319)364-0855.
Batteries Plus has stores across they country and some have
rebuilt Uniden NiCd packs for under $20.
--
==============================================================================
Bob Parnass, AJ9S parnass@bell-labs.com
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