Hi. My old FM stereo receiver SA-360 (same as SA-460)has stopped
producing a stereo signal when in FM mode. When I push the auto/mono
FM mode button, nothing changes now. Everything is monaural. This just
started happening. Every other mode works fine in stereo. I do not
have a schematic for this unit nor can I find one. Is there a cap
which controls this circuit perhaps? Anyone have any ideas how to fix
this? Antenna, signal strength etc all OK. Thanks....
Jim

This type of fault can be complex for you to fix yourself. The FM multiplex
decoder IC or circuits involved may have a component that failed. If the
tech is not familiar with the receiver design, a service manual will be a
must to have.

Did you check to see that your set does not have the FM muting turned off,
if your set has this option. Some receivers have an FM muting mode. When
turned off, the FM will be in mono. This is to suppress background noise in
the FM reception of present, due to low signal conditions.

The main things to check are that the MPX circuits are getting proper
voltages from the supply, and that the reference carrier from the received
stations are reaching the decoder.

In some of the older receivers, there was a small incandescent light used
for indicating the presence of FM stereo. If this light is burned out, the
decoder would stop working. It was used as part of the bias supply for the
decoder circuits. If your set uses this type of incandescent type lamp for
this, check that the lamp is good, in case your set is of this type of
design. This is really the only check you can do at home without all the
necessary test equipment, training, and service manual.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"Butcher" wrote in message
m...
Hi. My old FM stereo receiver SA-360 (same as SA-460)has stopped
producing a stereo signal when in FM mode. When I push the auto/mono
FM mode button, nothing changes now. Everything is monaural. This just
started happening. Every other mode works fine in stereo. I do not
have a schematic for this unit nor can I find one. Is there a cap
which controls this circuit perhaps? Anyone have any ideas how to fix
this? Antenna, signal strength etc all OK. Thanks....
Jim

Butcher:
Does your receiver have this problem with ALL stations that you can tune
in?..... or just a few? ? ?
Fixing this stuff just ain't this simple...... probably NOT a "cap which
controls this circuit"...... and without the proper test equipment and
tools, electronics knowledge, repair experience, etc...... a schematic will
not be much help...... there are no step by step troubleshooting
directions..... a schematic will only be most useful to a trained
technician that knows how to use it.
The fault you described could be caused by a lot of things..... shorted or
open diode or other semiconductor, faulty solder connection, faulty chip,
and yes a bad cap !
You might want to TAKE your nice vintage receiver to a service shop for at
the very least a repair cost estimate so you can make an intelligent repair
decision with facts instead of internet or telephone guesses. The worst
thing you can do is to get in there and start adjusting coils and pots......
the repair price will certainly be higher if you do.
--
Best Regards,
Daniel Sofie
Electronics Supply & Repair
-------------------------


"Butcher" wrote in message
m...
Hi. My old FM stereo receiver SA-360 (same as SA-460)has stopped
producing a stereo signal when in FM mode. When I push the auto/mono
FM mode button, nothing changes now. Everything is monaural. This just
started happening. Every other mode works fine in stereo. I do not
have a schematic for this unit nor can I find one. Is there a cap
which controls this circuit perhaps? Anyone have any ideas how to fix
this? Antenna, signal strength etc all OK. Thanks....
Jim

I guess I was more fortunate with a similar situation. I've got a big portable
zenith phono/radio combination with swing-out, detachable speakers. The thing
weights about 50 pounds. Removing the back revealed several schematics, one in
particular for the FM multiplex section which labled about six transistors and
their functions. It was easy for me to pinpoint the problem.

Bobby Basham
Tucson, AZ

wrote in message
om...
Hi. My old FM stereo receiver SA-360 (same as SA-460)has stopped
producing a stereo signal when in FM mode.