GrahamH:
You didn't happen to leave on a tape monitor switch or a mute switch ?

The beautiful thing about repairing STEREO equipment is that you have
redundancy in the fact that there are 2 identical channels and
corresponding circuitry. It would be quite unlikely that there are
identical failures in both the left and right channels.... a good
suggestion is that you should look for things that will affect BOTH
channels, like switches, jumpers, special modes of operation, and the
power supply, etc.
Based on your last comment regarding the Main-In terminals the problem
is most likely in the Main Power Amp (not the Pre-Amp) since it does
not output any signal to the speakers when you applied a good line
level signal to the Main-Amp inputs. If both channels are affected
the place to start looking is the power output stages.... if just one
of the channels is bad, the speaker relay will not enegize thus both
channels will appear dead.
By the way, as you said... you checked the main B+ voltages of +/- 44
VDC, but what about the B+ that supplies the lower regulated voltages
to the preamp and drivers? A lot more investigation can be done
without a schematic just yet. You might want to go to the website for
this newsgroup and look over the weath of troubleshooting and repair
tips...
http://www.repairfaq.org/
plan to spend some search time there and dust off your test meter and
oscilloscope and perform some more troubleshooting.
electricitym
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