From: parnass@cbnewse.cb.att.com (Bob Parnass, AJ9S)
Subject: Re: Bearcat 300 problem, help please
Organization: AT&T Bell Laboratories, Naperville, IL
Date: Mon, 12 Oct 1992 04:16:41 GMT
Followup-To: alt.radio.scanner
Summary: fixes for Beacat BC-300

In article <1992Oct11.150130.3809@vax.muskingum.edu>,
re_sims@vax.muskingum.edu writes:
 
> I have a Bearcat 300, and it has a problem, the display does not
> come on right away, after a few minutes it comes on dim and then gets
> to half brightness....  

The Bearcat BC-300 scanner has been  around  for  12  years.
Here  is a reprint of an article I published in my column in
the August 1989 issue of the RCMA Journal.


                    DON'T JUNK THAT OLD BEARCAT BC-300

       Although the Bearcat BC-300 scanner is no longer  available,
       it  occupies a fond place in my collection.  I exercise lit-
       tle self control when I see a used BC-300  for  sale  cheap,
       and  have  adopted  two broken units.  They make fine radios
       after repair.

       The BC-300 was the forerunner of today's 760XLT.  It  was  a
       50  channel  feature  laden scanner, introduced around 1979,
       back when Bearcat was part of Electra.  Retail sales of  the
       BC-300  continued  until  1987,  when it was discontinued by
       Uniden.

       Although Electra offered the pricey BC-350 as a  step  above
       the   BC-300,  firmware  bugs  and  a  batch  of  bad  power
       transformers doomed the 350, and the 300 remained the  jewel
       of Bearcat line.

       It's easy to see  why  the  BC-300  model  was  offered  for
       several  years.  It boasted premium features like a clock, a
       carrier operated solid state relay for tape recorder activa-
       tion, a transmission counter, and a Service Search of 11 ROM
       banks of preprogrammed channels.   For  memory,  the  BC-300
       used  EAROM  (electronically alterable read only memory), so
       backup batteries were not necessary.  The Dog House, a radio
       shop  in Fairfax, Virginia, at one time offered the DH 1000,
       a 1,000 channel adapter for the BC-300!   Unfortunately  for
       federal  band  listeners,  the BC-300 lacked coverage of the
       138-144 and 406-420 MHz bands.

       While outwardly impressive, internal construction was  typi-
       cal  of Electra hand wiring in that era -- a bit messy.  BC-
       300 schematics show at least 100 components changed  between
       earliest  and  later  units.   The scanner went through many
       circuit design changes, but rather than changing the printed
       circuit board, new components were tack soldered on the foil
       side in different positions.

       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, "P2284" denotes the radio was
       made  in  the  Puerto  Rico  factory during the 22nd week of
       1984.

       Switching power supply failure was common in early units due
       to  insufficient capacitance.  Electra responded by increas-
       ing the value of capacitor C98 from 22 ufd/16 v to 47 ufd/25
       v,  but I recommend 47 ufd/35 v.  If your display is getting
       abnormally dim, C98 is probably the culprit, as  it  was  in
       five Bearcat scanners I fixed.

       Squelch preset potentiometer R81, mounted on the radio  cir-
       cuit  board,  was  misadjusted in new units, requiring read-
       justment after the components aged.

       In one radio, I replaced Q9, a small signal PNP  transistor.
       Its  failure caused the BC-300 to become deaf on all but the
       UHF band.  Failure of squelch gate transistor Q15 caused the
       squelch to remain open at all times.

       Cold solder joints, especially on the wires and ribbon cable
       connecting  the  radio  board  to the logic board, have been
       responsible for other failures.

       I have seen serious  IC  failures  in  three  BC-300s  built
       around  1984.   These  include  CPU  chip IC201, memory chip
       IC202, and IC203, not in stock  at  your  your  local  Radio
       ShackO.

       The BC-300 circuitry, especially on the radio board, is very
       similar  to  the  circuitry  in  the  the  BC-220, BC-20/20,
       BC210XL, and BC-350, so some of the previous remarks may  be
       applicable to these models as well.

       I can neither furnish schematics nor repair your radio.   If
       you  come  across  a  broken BC-300, obtain a schematic from
       Uniden and spend some time troubleshooting.  If you give up,
       your  BC-300  can  be  fixed by Electronic Repair Centers in
       Franklin Park, Illinois, (708)455-5105.  I'm  told  they  do
       good  work.   The  BC-300 is a classic scanner and worthy of
       your efforts.

-- 
==============================================================================
Bob Parnass, AJ9S  -  AT&T Bell Labs  -  parnass@ihlpm.att.com - (708)979-5414