On the attached schematic, can someone tell me what might be the cause for the voltage at C being too low?
There are two pictures of the schematic; at the lower right-hand corner of "New Image" you can see the point "C" coming out of the power supply. In "New Image b" you can see where point "C" connects into the FM tuner circuit (which is not working). Transistor voltages for Q4, Q5 and Q6, that should be 7.3 are down around 4.3.
So this is not an "independent" voltage; when I isolate that juncture of 100mf capacitor and 1800 ohm resistor at "C" by the power supply (disconnecting it from the tuner circuit), I get like 17 volts; when I connect the two "C"'s it drops to 4.5. I would have thought (being electronically naïve) that the voltage at "C" would be constant no matter what was connected to it, as it's a power supply source. But NO...
Transistors Q 4,5 and 6 test good. Could there be a bad transistor in the tuner circuit - or what?
I believe that the speaker leads were shorted at one point, which caused transistor Q106, one of the output transistors, to fry. But how could that have caused voltages at "C" to drop?
I'd appreciate any help. I just don't have the expertise or experience, and I'm baffled.
Thanks,
Bob H.