My nephew bought a BC142XLT at a tag sale to try out scanning. It
worked for a less than 15 minutes, but then the display went dead and
there is just barely a hiss from the speaker no matter where the
squelch is set. He brought it to me to try to fix it. I'd like to show
him that you can still work on your electronics since this is all
through hole construction.

My first question is there a schematic out there I can get for free?

My next question is does the following troubleshooting information
make any sense to anyone?

I have opened up the unit and probed around a bit. The 8V regulator is
putting out 7.95V which looks good. The electrolytics don't look
tired. It looks like the receive section works because I get what
sounds like receive audio hiss from the audio noise output pin of the
MC3359 FM demodulator chip. It also looks like the audio secion works
because when I put my fingers on the input lines and around the
circuit I get some feedback and noise from the speaker.

I assume the UC1116 is some kind of controller. It looks pretty dead.
I probed the keyboard inputs and the ones that are not ground stay at
3.5V. There is no pulsing as I would expect if the controller was
scanning the keyboard. The diplay lines are mostly at 6.5V levels with
no pulsing I would expect if the display was being scanned. Not a
single segment comes on. There is a 390 ohm resistor that looks like
it got hot. This drops the input power to about 5.2V. This voltage is
present as long as the power is plugged in even if the switch is off.
There is a sine wave of 383khz at UC1116 pin 16.

There is an interesting circuit that is generating 20V and apparently
driven by an LM386 audio amplifier through a multiplier. I thought
this might be for the display, but the signal runs to a Harris chip on
the RF side of the board.

Any help would be greatly appreciated.

Thanks,
Ted

There is some info in the Scanner Repair & Modification Manual. Just happens
to be one at Ebay, item number 5728429712.

Ted, I tried to reach you of list but your email is no good. I have a 142
XL here I can meter out any segment you want me to. Write back direct.

Ronny K4RJJ


"Ted Busky" wrote in message
om...
My nephew bought a BC142XLT at a tag sale to try out scanning. It
worked for a less than 15 minutes, but then the display went dead and
there is just barely a hiss from the speaker no matter where the
squelch is set. He brought it to me to try to fix it. I'd like to show
him that you can still work on your electronics since this is all
through hole construction.

My first question is there a schematic out there I can get for free?

My next question is does the following troubleshooting information
make any sense to anyone?

I have opened up the unit and probed around a bit. The 8V regulator is
putting out 7.95V which looks good. The electrolytics don't look
tired. It looks like the receive section works because I get what
sounds like receive audio hiss from the audio noise output pin of the
MC3359 FM demodulator chip. It also looks like the audio secion works
because when I put my fingers on the input lines and around the
circuit I get some feedback and noise from the speaker.

I assume the UC1116 is some kind of controller. It looks pretty dead.
I probed the keyboard inputs and the ones that are not ground stay at
3.5V. There is no pulsing as I would expect if the controller was
scanning the keyboard. The diplay lines are mostly at 6.5V levels with
no pulsing I would expect if the display was being scanned. Not a
single segment comes on. There is a 390 ohm resistor that looks like
it got hot. This drops the input power to about 5.2V. This voltage is
present as long as the power is plugged in even if the switch is off.
There is a sine wave of 383khz at UC1116 pin 16.

There is an interesting circuit that is generating 20V and apparently
driven by an LM386 audio amplifier through a multiplier. I thought
this might be for the display, but the signal runs to a Harris chip on
the RF side of the board.

Any help would be greatly appreciated.

Thanks,
Ted

I also tried to e-mail him to no avail. I also repaired one at some point.
If memory serves me correct, it was an Electrolytic cap and a zener went bad
in the power supply section. In his initial post (as included below) he said
"the electrolytics don't look tired." I'm guessing he meant he was looking
for them bulging out at the bottom as is "a" sign. Though you may not see
the bottom bulging, it isn't the only sign a cap is bad. You have to remove
them for testing - if in doubt. They can be leaky or open and you wouldn't
know it to "look" at it. If you can't "''test" the cap, then replace it if
possible to eliminate it as a cause. Also your method of checking a IC isn't
good either. Unless it looks cracked, bubbled - to show actual damage or
possible damage - it can be bad with no outward appearance. OR it could be
good! You have to check voltages and see what is what. You can't just assume
it is bad. An IC needs the "supply" voltage and a ground to start. From
there, it needs all the necessary input voltages to work. IF the supply
isn't there, the ground or an input and ultimately an output voltage, then
something is wrong. NO input voltage chip, no output. No supply voltage, it
won't work. Same with ground. IF input but no output, then you can say that
part of the chip is shot. Never just assume the chip is bad. That is bad
because some of those parts are no longer available. You could end up
tossing an otherwise repairable scanner with that assumption. It sounds like
"A" section of the power supply was checked, but not all. IF any of the
others are bad, could be why the pulses are missing. When I do repairs like
that, pulses are not what I look for. I look for what brings the display
back and audio. The keyboard pulses will be later when I can see any actions
on the display and hear any results. I think you're looking in the wrong
area. Concentrate on the "Display" and Audio issues which most likely will
be a power supply defect. Does no good to play with the keyboard when it
won't show up on the screen!

Of the many manuals I have, I thought I had the repair manual here for that
unit, but I don't. I've repaired enough radios to be able to have some idea
as to condition. I hate working on radios with no schematics, but I've done
it and succeeded. It is all in a matter of going about it in an organized
manner. Not "assuming". Checking to see what works and doesn't and get an
idea as to HOW things are supposed to work. The power supply is a good start
in any failure where two or more symptoms appear.

Not having the schematic myself, I can't be of more help without the unit.
But going on past repairs, I've offered my results.

Lou

"Ronny Julian" wrote in message
...
Ted, I tried to reach you of list but your email is no good. I have a
142 XL here I can meter out any segment you want me to. Write back
direct.

Ronny K4RJJ


"Ted Busky" wrote in message
om...
My nephew bought a BC142XLT at a tag sale to try out scanning. It
worked for a less than 15 minutes, but then the display went dead and
there is just barely a hiss from the speaker no matter where the
squelch is set. He brought it to me to try to fix it. I'd like to show
him that you can still work on your electronics since this is all
through hole construction.

My first question is there a schematic out there I can get for free?

My next question is does the following troubleshooting information
make any sense to anyone?

I have opened up the unit and probed around a bit. The 8V regulator is
putting out 7.95V which looks good. The electrolytics don't look
tired. It looks like the receive section works because I get what
sounds like receive audio hiss from the audio noise output pin of the
MC3359 FM demodulator chip. It also looks like the audio secion works
because when I put my fingers on the input lines and around the
circuit I get some feedback and noise from the speaker.

I assume the UC1116 is some kind of controller. It looks pretty dead.
I probed the keyboard inputs and the ones that are not ground stay at
3.5V. There is no pulsing as I would expect if the controller was
scanning the keyboard. The diplay lines are mostly at 6.5V levels with
no pulsing I would expect if the display was being scanned. Not a
single segment comes on. There is a 390 ohm resistor that looks like
it got hot. This drops the input power to about 5.2V. This voltage is
present as long as the power is plugged in even if the switch is off.
There is a sine wave of 383khz at UC1116 pin 16.

There is an interesting circuit that is generating 20V and apparently
driven by an LM386 audio amplifier through a multiplier. I thought
this might be for the display, but the signal runs to a Harris chip on
the RF side of the board.

Any help would be greatly appreciated.

Thanks,
Ted