I came into possession of this beautiful old Pioneer SX-838 receiver a couple of years ago and I would like to fix this problem. After the unit has been playing for a half hour or so, irrespective of source, the left channel will drop out. When it drops out, it fades out over a period of a second or two. It does not cut out instantaneously.
To isolate the problem I switched the preamp-to-main amp connections in the back so that the left preamp channel feeds the right main amp channel and vice versa. The left channel continued to drop out. This tells me that the problem is in the main amp section (speakers are *not* the problem). I was hoping that the problem was in the volume pot, this behavior seems to rule that out and points to the left channel of the main amp section.
If I turn the volume up high enough the dropped channel can be heard faintly and if I turn it up even higher it will kick back in with a crackle and play okay for a while before dropping out again. To avoid blasting the volume out of the speakers when doing this I used the speaker button on the front to disconnect the speakers. This technique resurrects the channel as well as when I leave the speakers connected. This seems significant as turning the volume up past a certain point resurrects the channel whether or not current is flowing through the circuit. Apparently, the higher voltage applied to the circuit is enough to do the trick.
When the channel drops out, I can power down the unit for 10 or 15 seconds and when I turn it on again the channel is still out.
Can anyone suggest to me which type of component(s) might be causing this behavior, resistor, capacitor or semiconductor? I have the schematics and I don't see any coils. I don't suspect the power supply because both channels seem to be powered by the same circuitry and if one channel went out, both would go out.
I don't have a scope or a signal generator for probing the circuit, just an analog and a digital meter.
Any help appreciated. Thanks