"Dave" wrote in
et:


"Mark D. Zacharias" wrote in message
. net...
Arfa Daily wrote:
"Mark D. Zacharias" wrote in message
. net...
Arfa Daily wrote:
"Dave" wrote in message
. net...
I have an old Yamaha CR-820 receiver/amplifier that no longer
has any sound output. The meters still show signal strenght when
a tune across the AM/FM bands but I get no audio from the
speakers or the phone jack. No hiss. hum, carckle or pops. JUst
solid dead silence.

It isn't worth sending out for a shop base repair.

Has anyone has a similar problem? Does anyone know where I can
obtain a schematic or service manual?




If it's nothing straightforward like a failed ( rather than blown
) fuse, then it's most likely that the speaker protection circuit
is operating because of a blown output stage. I've a vague
recollection that this one uses an output hybrid ( big black "IC"
bolted to the heatsink with type STK-xxx ) and if so, it is likely
that this is your problem. Some of these can be very expensive,
and many of the older ones are now obsolete and hard to obtain. If
it is one of the models that uses discrete output stages, then you
might struggle to get to the bottom of its problems, particularly
without a set of schematics, which again, might be difficult to
find for an item this old.
Arfa

The CR-820 uses discrete transistors, but the repair isn't for
newbies - there's fusible resistors inside asbestos tubing which go
bad, usually without any visible clue, and the layout is hardly
service-friendly. Mark Z.

OK, much like the modern Yammy AV amps then ...

Arfa

Well, they aren't flat packs - they're TO-3's - 2SB557 and 2SD427
IIRC.

Four-gang (once again, IIRC) tuner, all analog, silver face, wood
cabinet, rectangular metal knobs, and lots of 14 volts lead-lamps
which burn out...

mark Z.


. If I run the amp with both left channel transistors out of the
circuit the right channel works fine.
I replaced a bad outout transistor after checking it. Now when I turn
the receiver on the main power fuse blows.

My guess is that the original failure took out the power transistor
before the fuse blew.




Your best bet is to replace all output transistors (left and right
chanel), check all the smaller transistors in the area, and check the
emitter resistors for the outputs (usually 2 small value {~.47 ohms or
less} resistors in one 3 pin package with a common leg in the middle)

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