Quote from: mandu on June 19, 2022, 10:23:46 AMI would suggest you experiment with those old electrolytic capacitors before throwing out to learn something and acquire some knowledge out of it. Regards.

Yes this is a good idea.  And running the charger with a limiter lamp will avoid the overheating that you experienced, and sometimes bring them back to life if you are patient.

Quote from: BenGunn on June 03, 2022, 06:22:21 AMMaybe I'll wait for an answer from other members of the topic?

I sent a PM to bajaman for you.  Hopefully he will respond in this thread.

So it seems the problem is on the -48V rail.  I'm not sure why it didn't show up when you measured the AC volts there before.

Check that the solder is good and there are no broken pads at C48.  Sometimes the pads break near the cap and you can't see it because the cap is glued down.  Measure resistance from the (-)lead of the cap to Q2 collector just to be sure.
If no solder or pad/trace issues, replace C48.

So there is excess 100Hz hum in both the preamp and the power amp.  That pretty much narrows it down to the power supply.
Recheck again the DC and AC volts on the power supply rails.

That is a substantial difference.
I searched for "100Hz squarewave" on youtube and it sounds pretty much the same as your soundfile in post #41.
Are you on 50Hz 240V power?

Can you run the 'preamp out' to another amp and see if it has the same sound?

Quote from: FenderDeluxe112Plus on May 30, 2022, 07:31:21 AMWith a jumper to ground at cr3 anode the buzz is there but quieter.

Better if we can put some numbers on it.  Measure AC volts across the speaker terminals with and without the jumper.

So that sounds like oscillation to me.
Try jumpering CR3 anode (or CR4 cathode) to ground and check if the oscillation sound is still there.

Quote from: FenderDeluxe112Plus on May 29, 2022, 03:18:32 AMCr13 and 14 have a forward voltage of 0.5 which seems ok.

Reversed they read 1.9020 and 1.8064
Does that check out ok?

Yes that seems right.
In post #41 sound file, is that the sound it makes with no signal, or is that with a tone at the input?

Quote from: FenderDeluxe112Plus on May 28, 2022, 04:53:24 PMQ9
Pos to collector com to emitter .8232

That seems a bit suspect.  Have Q8 and Q9 been replaced?
I would remove them and re-check them out of circuit.

Also, have CR5 thru CR12 and CR39 thru CR42 been checked in circuit?  Just looking for proper .4 to .7V readings forward biased, and no shorts.

That is really strange.  There is no where for that extra couple volts on Q8 collector to come from. 
If it were a solder bridge, it's unlikely the same exact thing would show up on the negative side (Q9).
So I would guess it's either an oscillation that the meter is interpreting as DC, or it's just a ghost reading and irrelevant.

Do Q8 and Q9 check out ok with diode check in circuit?

That's good.  Now measure DC voltage at CR39 anode and cathode.

Quote from: FenderDeluxe112Plus on May 28, 2022, 02:07:53 PMContinuity between cr39 anode and Q1 base.
Continuity between Q8 collector and cr39 cathode.

Please specify reading in ohms.  Continuity is a somewhat vague term that changes depending on model of meter.  If relying on a meter beep for continuity, it can range anywhere from zero to 200 ohms.

According to the schematic, that is impossible.
So something funny, or we don't have a schematic match.

Check resistance from CR39 anode to Q1 base.  And resistance from CR39 cathode to Q8 collector.
Same for CR40 to Q2 and Q9.

You cannot view this attachment.

Double check those collector voltages for Q8 and Q9.
Where could they be getting a voltage higher than the base voltages of the outputs?
(ex. Q1 base is 1.2V, Q8 collector gets voltage from that line)

Good so far. 
How about DC voltages for E,B,&C of Q1,Q10,Q2,Q11
Also Q8 and Q9