"Arfa Daily" wrote in message
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"John Keiser" wrote in message
news:48qdnVyu_aVeyq7TnZ2dnUVZ_qadnZ2d@powerusenet. com...
I've owned this receiver/amp for 30 years. Used infrequently but
functioned fine. Today, while playing a CD, suddenly stopped after 5
minutes on low setting. Toggled to mute, loudness, no joy. Using FM
input, controls seem to work and I can hear music when I reach very high
settings. Sometimes crackles to very loud but only momentary. I think
pre-amp is OK.
I'm thinking some sort of protective output circuit has activated but I
have no schematic. Before I tear in blindly, does anyone have access to
a schematic for this [I found a source on rapidshare but file no longer
there].
Thank you.


The service manual is available for free here

http://www.hifi-manuals.com/Pioneer

You need to create an account, but it costs nothing. Your problem sounds
possibly power supply related to me. Mr Cook quesried the fact that you do
not appear to be recording any low negative rails, and that would also be
a concern to me. If you look on the first schematic towards the top left
of the enclosed area marked "POWER SUPPLY CIRCUIT", you will see a pair of
low rails (+ / - 15 v ) marked

"( EQ.AMP TONE CONT. VCA IC) " The +15 v reg is a 3 terminal 78 series,
but the negative regulator is discrete, constructed around a pair of
transistors. I would suggest that it might be a good idea to check that
those rails are both present, and finding their way to the indicated bits
of circuitry. Now comes the tricky bit. The schematic, although a
perfectly complete and valid looking one, sadly has no component refs on
it, which is going to make finding those devices a bit more of a hunting
trip, than would otherwise be necessary. Strangely, however, the PCB
overlay diagrams are fully annotated ...

Arfa

Sorry about top/bottom posting thing. Maybe this is on the bottom? I just
use OE to read, rarely post.

The schematic is complex but a big leg up.

Thank you all.

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