I am more of a tube radio guy, but I am trying to figure out a low output channel on a friend's solid state amplifier. I have tracked down a number of symptoms and I am hoping that someone might be able to help me with a diagnosis. I would be very appreciative of any ideas you might provide. The schematic for the Front Amplifier board is shown, but I am not sure if it will be legible.
Thanks as always for any help/suggestions/insights/next steps you can provide.
Andrew
- There is very low output on the front left channel, regardless of the input source. (Yes, speakers have been switched - problem remains on the left side.)
- When the receiver is turned on, the left channel is too quiet to hear, but slowly increases in volume until it is about 25% of the right channel. The sound is intermittent until the volume is increased, when it becomes steady, though quiet.
- A number of component in the left channel are warmer than those on the right. For example, R521 (right channel) is 44 C, while its corresponding resistor on the left (R522) is 51 C. R523 is 31 C and R524 is 44 C. More interesting is that C525 (470 uF / 63 V) is 29 C and C526 about 36 C.
- Measuring the Voltage at the idle current measurement points, I found the right channel measurements at P501 to be 4.9 mV DC / 0.1 V AC, whereas the corresponding left channel measurements at P502 were 21.6 mV DC and 0.02 V AC. Cap leakage?
- The problem is unlikely to be in 10,000 uF filter caps (C561 and C562) as they feed both right and left channels.
Thanks as always for any help/suggestions/insights/next steps you can provide.
Andrew
Did you ever figure this out? I actually have both channels nearly no output, but I've narrowed it down to the multichannel board where it seems all the preamp IC"s are. I already recapped both amp boards to no avail, but it needed to be done anyways.