Did it get wet?
If so, did you pull it out of the sink to see how bad the bottom of the board was corroded?
If so, did you pull it out of the sink to see how bad the bottom of the board was corroded?
Is the red jumper that you added?
I need a high quality photo (in focus, good lighting.. ) of that area of the board.
I need a high quality photo (in focus, good lighting.. ) of that area of the board.
Could it be that they installed an op-amp in place of a comparator and that's causing part (all) of the problem?
Is the circuit for that IC in your amp the same as the circuit for the 393 in the diagram?
Is the circuit for that IC in your amp the same as the circuit for the 393 in the diagram?
The 393 was installed backwards.I install it the right way and removed the jumper that was on the op-amp.Vcc voltage is not reaching the 3525. pin 1 an 7 of the 393 has 12v.I see no voltage on the base of Q24 in the schematic
The IC with the jumper was a 4558. Was it the same location that's the LM393 in the diagram?
If so, did you replace the 4558 with a 393?
If so, did you replace the 4558 with a 393?
Both was in the right location but the 393 was installed in the opposite direction.
I now install a new 393 and it power up and has good audio.
I now install a new 393 and it power up and has good audio.
This amplifier was either designed by Robert Zeff (Zapco, ARC...) or is a clone of one of his amps.
Yes. They rectify the drain voltage/waveform and use that to supply the IC, via a voltage regulator. It ensures that the drive voltage doesn't go low when B+ goes low.