"Mr. Land" wrote in message
ups.com...
On Aug 1, 6:06 pm, "David Farber" wrote:
This Sony STR-AV970X powers up ok, relay clicks on, but there's no audio
at
the speaker outputs. I don't have a schematic so the only information
I've
been able to figure out is that the output transistors have no bias
voltage
on them and consequently there is no bias current across the emitter
resistors. There are just the supply voltages coming into the collectors
which are +/- 51 volts. The low voltage supply is putting out +/-12
volts
and +5 volts at the regulator sources. Sitting in the middle of all this
is
a dual voltage amplifier, an STK3102III, which I suspect may be faulty
but I
was wondering if somebody could tell me where the low voltage supply
enters
the mix in the power amplifier section.

Thanks for your reply.
--
David Farber
David Farber's Service Center
L.A., CA

I think I may have worked on one or two STR-AV*'s in a former life...

Seems like 100% of the cases where the outputs were NOT bad, it was
the STK* that was bad.

Not sure what you mean by "enters the mix" but the STK's typically use
op amps, and I've seen cases
where they go bad, and output a DC voltage which drives the outputs
hard off.



I wish there were some kind of DC voltage. The offset is zero. The driver
and output transistors have no base-emitter voltage on either channel. It
would seem to me that the STK-3102III would not want to output any DC to the
amplifier input. I recently repaired a newer Sony receiver that had some bad
digital muting transistors. That prevented the low voltage from reaching the
driver stage. I was thinking something similar was going on here but without
a schematic, it's tough to figure out.

Thanks for your reply.
--
David Farber
David Farber's Service Center
L.A., CA