That's strange. Now voltage is about 36 on both outputs.

This may be my intermittent that's frying the finals.

 

So far so good.
Good output on both sides.
Current seems normal.

The hot-rodded side with the new drivers is a little ahead on gain.

Now I'm back to square one. Not knowing what caused the failure.

 

Original 2sc756 pair on right board .
New MJE15034 pair on left.

Cleaning costs extra.

 

Any chance the bias has drifted (vr802) or gain vr801?

 

I don't know proper adjustment.
I did adjust, while measuring center dc output voltage. No change.

Of course, that may have been when I was having problems???

 

That may be it. Now 802 changes the center (operating) voltage.

I'll hope it just needed cleaning by turning.

 

Back to the drawing board. Put current limit resistors back and powered up today. After sitting a few days.

Back to center voltage being pulled down and high standby current.

Jumper BE of tr803 cuts current.
VR802 no effect.

 

Matched transistor sets.

 

I should have a matched set. They are three originals.
I could try the different combinations.????

Can I find them with a simple dc beta tester?

So, maybe nothings wrong?

 

That is one way of doing it. Try it.

 

A matched pair of output transistors from Newark is $15.75. Think about it.

 

That would be no problem, if I had confidence in it working.
I don't want to spend good money after bad.

 

Same symptoms with the good side transistors in the bad side.

 

Driver transistors........Good trouble shooting.

Purchased transistors in the good side.

 

I have new drivers installed.
I'll pull and test them. (and match)Have extra.
It may be, the mismatched finals killed the drivers again. They really suck, beta wise. As do the good side ones.
Need a new battery for my beta tester. Hasn't seen the light of day for 10 years.

If driver died, this may be my final (pun) attempt.
This is really just silly! Friend said not to bother with difficult repair.
I'm just embarrassed, as it should have been simple!

 

I'm just embarrassed, as it should have been simple!

I'm sure we've all felt that and we've all spent far too much time to end up with nothing. Geeez it's hard to walk away.

 

I'm back another stage.

803, 805,806, 807, 808 replaced. 804 pnp seems fine.

Same problem.
Took out 802 with difficulty. I'm losing patience.
Checked great. Much better than other. 756s.
Put it back, and everything is fine again.

I must have another 756 somewhere, that was removed. Or another new replacement.
Next failure I'll go right there. (802)

 

This may go down as one of my more frustrating repairs.
Worked perfectly all day yesterday. Hot and cold spray.

New finals and drivers.
Tried new tx in the next stage back when not working. They tested fine so I put in originals.
Then I removed TR802 which tested fine.
Put it back and things worked fine all day.

Plugged in this am and I'm back to high standby current through finals.
Thanks to earlier suggestion, I have a more or less permanent 60 ohms in series, and monitor V drop continually.

I will now cool and heat TR802, and replace it either way. This is about my last chance at success.
I've been busy with other things. Don't have the will right now to make a step by step comparison to good side. It's shotgun or "the shotgun.

 

Aha, heat brought it back.
Not in the TR802 area though. Unless I wasn't patient enough. I move quite quickly to another error.
Now it should be just a matter of time to find the right resistor/part.
It may take a day between tests though.

 

D802
After seeing R814/33ohm follow the problem, swapping didn't help.

Now D801 seems likely. I can heat and cool to change symptoms.
I'll see what it does out of circuit. Could be the TR803, but I've swapped it before.