Cause of Bearcat Scanner Shutdown Help!
 

On Wed, 24 Sep 2003 21:17:48 +0000, Nick wrote:

My mothers friend wants me to try and fix a older Bearcat scanner
model 250 that shuts down after being on about 20 minutes. After the
cool down it seems fine. Everything works well otherwise. What to look
and change for myself help is appreciated. Nick

If the circuit breaker inside the power transformer was bad,
the scanner would be dead and stay dead.

Based on your description, I would first replace Q204, a TIP29
transistor located on the Feature board. When you install
a new one, install some type of heat sink to the tab to prevent
the replacement from overheating. I sometimes homebrew a
small heat sink from 2 solder lugs and fastening them
to the tab using a screw, lockwasher, and nut.
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Bob Parnass, AJ9S GNU/Linux User http://parnass.com

Nick,

Stepping back a bit, I should have suggested you
try powering the BC-250 from a good, external 12 - 13 VDC
power supply instead of from the AC wall outlet.

If the BC-250 works consistently well for a long time when run from an
external battery or 12 - 13 VDC power supply, then I would
suspect a defective component in your BC-250's power supply stage.

I'm not sure I understand which transistor you removed.
If it is under the main power transformer, then that's
not the transistor I mean.

Transistor Q204 is on the smaller circuit board.
Turn the BC250 upside down, with the case off.
Notice the smaller (approx 3" by 5") circuit board,
called the Feature board. It is located towards
the front edge of the scanner and has a flat ribbon
cable soldered to it. There are 2 huge ICs in sockets
on it, as well. The feature board contains the CPU and
digital logic for the BC-250.

Transistor Q204 (Texas Instruments TIP-29)
is located near the upper right hand corner
of the Feature board. The TIP-29 has a metal tab with
a single hole drilled through it and runs too hot.


On Fri, 26 Sep 2003 23:40:55 +0000, Nick wrote:

On Wed, 24 Sep 2003 21:17:48 GMT, Nick wrote:

My mothers friend wants me to try and fix a older Bearcat scanner
model 250 that shuts down after being on about 20 minutes. After the
cool down it seems fine. Everything works well otherwise. What to look
and change for myself help is appreciated. Nick


Bob; I took out the power transistor with the 3 leads soldered and
can't find one now. Rat Shack does not have them and still looking on
net. It was real hot if that was proble, Allaround it seemed
blackened from heat but not blown. Hope that is what it is. Not even
sure of name. Would sit under the soldered side under the power
transformer and from the underside near the largest can capacitor and
has a tri axial lead near the squelch wire solder point. It has a
hole on top but no heat sink of any kind to disapapte that kind of
heat. Says from what is readable Texas Instruments and some number
but no rating etc. Any more help here. Is this the tip 29 power
transformer that usually is the culprit. Nick

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================================================== =======================
Bob Parnass, AJ9S GNU/Linux User http://parnass.com