"Bob E." wrote in message
...
Pressing the power button gets relay click and power LED flash (on volume
control) but all shuts down immediately.

Looked for infamous "pink cap" on "sub power supply" (there is one) and
replaced but no change in symptoms.

Jumpered the relay contacts and using a Variac ran voltage up full (while
watching main transformer secondary voltages): all seems normal but still
no
signs of life. Transformer voltages are as expected (2 pairs of windings;
each pair share a common center tap, total: 4 windings, all voltages
increase
linearly with increase of primary V). Still no display or control
functionality at all.

Pressing the power button (with jumpered relay and full mains voltage
applied) gets same symptoms.

So far I think I can rule out a shorted output device.

How best to proceed with the troubleshooting?

Ideas?

I have the service manual.

Thanks.



If that's one of the ones with the little sub PSU, there's also a 4013 chip
on there that is a good place to monitor the supply volts. Those volts feed
another little circuit on the board that generates the reset pulse for the
system control micro. Unless that pulse is sharp and of sufficient
amplitude, the micro never boots. When you checked for the bad cap that's
notorious in those models, are you absolutely definitely sure that you
picked the right cap ? I only say that because there are several slightly
different versions of that sub board, and on more than one occasion, I've
just gone for the obvious looking one without checking, and it has in fact
been another one entirely that has been the bad one. You can usually be
pretty sure that it is the cap, if you check the supply volts to the IC. Use
its pin 7 as the ground, and then check pin 14. Should be about 8 volts.

I've just had a squint at the schems for a couple of models from the same
series, and the cap is called C4 on one of them, and C405 on another. I also
have a note on the diagram saying that it's called C3015 on yet another
version.

A long time ago, I did have a few of these big Yammy AV amps that had faulty
5 volt regs in them. They are located on a heatsink running across the front
of the amp, and facing the back as I recall. They are 'oddballs' I seem to
remember, with 4 or 5 pins on them, and the faulty ones I had, produced low
output, rather than none at all. I'm sure Mark Z will be able to confirm all
of this, as he has worked on them a lot.

Arfa