William Sommerwerck wrote:
Transformer has stayed cool. The 3 amp fuses on the positive and
negative rails are not blowing at this point. I don't have a 'scope, but
have a line on a Philips PM3050 for $85. There is more going on here
than I can read at the moment. I have the output pair on the left channel
yanked at this point because they shorted out. Now the output pair on
the right channel are heating up when the power is on. The electro cap
that blew is on the right channel. Part of the 15 volt regulator circuitry
failed and I replaced some parts there. But that's it for tonight.

I think you have problems that go fary beyond a bad cap. I suspect the bad
cap is a effect more than a cause.

I would start by pulling the output pair on the right channel and trying to
get everything else working correctly.

Both output pairs are pulled.

I am reading 20 volts AC to ground on each of the stepped down leads from the
transformer and 40 volts between them.

The positive rail is reading 26.3 volts DC to ground and the negative rail is
reading 26.7 volts DC to ground after going through the bridge rectifier and the
filter caps. They are reading 53 volts between them. The replacement for the electro
cap that blew is reading 26.7 volts across its terminals. It connect the negative
rail to ground. Positive side is grounded. It is no longer heating up when power is on.

With power on and about to take some voltage readings across the empty output tranny
terminals on the CB, I noticed some tiny sparking going on at the edges of the trace
leading to the collector terminal of Q317, with occasional riny puffs of smoke (see
schematics):

http://www.davidreaton.com/PDFs/Adve..._schematic.pdf

I removed as much solder as possible from the traces around all output terminals
with a solder wick and cleaned up the board with switch cleaner. Sparking appears to
have stopped.

Began taking various voltage measurements at same points in right and left channels.
Discovered huge variation on voltage across C-E terminals with output transistors
removed. Right side had about 26 to 27 volts across the C-E terminals of each
output transistor. The left side had no voltage across C-E terminals of one output
transistor and about 52 to 54 volts across the C-E terminals of the other output
transistor.

Also had different readings across C-E terminals of the two pairs of differential
transistors at the input. Right side had about 26-27 volts across C-E terminals of
each transistor and the left side had about 7 volts across the same terminals.
Disconnecting the base of Q302 resulted in both differential transistors on the left
reading identical to the right side across the C-E terminals. I traced it down to
where D304 connects to the base of Q302 thru a 20K resistor, R336. I reconnected the
base of Q302 and disconnecting the cathode side of D304 and got the same results as
disconnecting the base of Q302. Now it's just a matter of going through the same
procedure until I find the faulty component.

Disconnecting the base of Q302 had no effect on the voltage measurements of the
output transistors in the left channel, but disconnecting D304 did. Reading across
the C-E terminals of one output tranny on the right channel with D304 disconnected,
the digital meter read about 27 volts and then began drifting steadily lower,
similar to reading a large cap with an ohmmeter. When I switched the meter to the
C-E terminals of the other output tranny on the right side, it read higher than 27
volts by as much as the first tranny's voltage diminished when it was read.

And that's where it stands. Sorry for not reading and replying to every post, but
when I got enough insight from what I did read to see where I needed to go, I
stopped reading and went to work. Will report all findings and methods used.

Thanks all

--
Einstein forgot to carry the two