Hi "Max" , as Skywatcher mentioned, welcome to the party! I've been very conservative chasing this issue since it began. Just to quickly recap:
> Receiver was playing loud, not cranked, about 85-90 db on my decibel meter from 10 feet from the speakers, about "10 o'clock" on the volume knob.
> I went over to investigate and could hear a very faint tinny sound out of the right channel. Left channel was dead
> Put the receiver in mono to see if i could get anything out of the left side, no go.
> Popped the cover and found both F1 and F2 open, F3,4 and 5 were OK. There is no smell of burining or overheating inside.
> Removed the driver board and looked for obvious physical signs of component failure, none found.
> Put a meter across both big filter caps, both act the same, voltage climbs to about a volt and then drops to 0 volts. Ohmed out , the resistance bounces around then stabilizes at 2K ohms on both big caps.
> Did the same test ground to positive side of big caps, similar result.
> I have not ohmed out thedriver transistors; I could do a quick check in the morning and compare readings from all 4 transistors in circuit to see if there is an indication of a short. At a minimum I can compare the reading from the left and right pairs.
The plan is to try three steps suggested by Skywatcher to isolate power supply issues from driver / output stage: install fuses, power up with F4 and F5 out, F4 and F5 in, and Driver board in, nothing attached, volume minimum, switch in aux.
If, between the two of you the consensus is I should pull the output transistors and do a diode bias test on them first is the correct sequence, I can do that. I am assuming that the case is the collector and the two pins are emitter and base.
One last thought I have is based on what I discovered when I opened the unit up. As noted, the workmanship on the driver board was pretty piss poor and the dirt and surface corrosion should have been taken care of when the unit was refurbed IMO. The four pots at the top of the driver board were not replaced and they look 40 years old.
Is there any logic to reaching out to the community and seeing who might have the time and expertise to rebuild these two boards? I have the technical ability to remove and replace them, set up biases, etc, and test and check the output transistors, install replacements, silicon the metal contact, etc.
It's just a thought. I don't have a thousand dollars to redo a recap, rebuild of the whole unit, but these two boards in particular look ratty and may be the rot cause for this issue. I'm getting ahead of myself but just thought i would put it out there. Thanks a bunch for the support! Skywalker, I will hold off on power up until I hear back from you tomorrow. In the meantime I am going to poke around the unit and take some further resistance readings from the driver board connector. Hopefully I can figure out the pinout between the board and the schematic, I don't see any pin number references on the board itself. Here are some updated, and hopefully better pictures of the driver board.