On this amp, there is a mix or right and wrong transistor layouts on the board. The square pad is always supposed to be pin 1 but that's not the case with this board. For this board, look at the face of the component with the text upright and the left pin is pin 1.
All of the readings for the points you measured seem to be OK. Reinstall the 6488 to see if it still powers up.
All of the readings for the points you measured seem to be OK. Reinstall the 6488 to see if it still powers up.
Amp worked perfectly for about 8 minutes then shut down. Monitored it for anything heating up. Nothing seemed to be getting hot. Warmest thing on the board was the Transformer at 102 degrees Fahrenheit.
Took the following readings after it shut down:
Opto:
Pin 1: +1.16
Pin 2: -0.00
Pin 3: -0.019 to +0.147 pulsing
Pin 4: +12.14
Pin 5: +12.32
Pin 6: +12.80
Small transistor (MPSA06 behind opto):
leg 1: +11.49
leg 2: +12.14
leg 3: +12.32
Thermostat:
+ 11.48 on both
494:
Pin 1: 0.00
Pin 2: +0.49
Pin 3: +0.49
Pin 4: +4.32
Pin 5: +1.48
Pin 6: +3.42
Pin 7: -0.00
Pin 8: +11.49
Pin 9: 0.00
Pin 10: 0.00
Pin 11: +11.49
Pin 12: +11.49
Pin 13: +4.92
Pin 14: +4.93
Pin 15: +0.49
Pin 16: 0.00
Just checked it again. Amp is intermittently powering up now.
Took the following readings after it shut down:
Opto:
Pin 1: +1.16
Pin 2: -0.00
Pin 3: -0.019 to +0.147 pulsing
Pin 4: +12.14
Pin 5: +12.32
Pin 6: +12.80
Small transistor (MPSA06 behind opto):
leg 1: +11.49
leg 2: +12.14
leg 3: +12.32
Thermostat:
+ 11.48 on both
494:
Pin 1: 0.00
Pin 2: +0.49
Pin 3: +0.49
Pin 4: +4.32
Pin 5: +1.48
Pin 6: +3.42
Pin 7: -0.00
Pin 8: +11.49
Pin 9: 0.00
Pin 10: 0.00
Pin 11: +11.49
Pin 12: +11.49
Pin 13: +4.92
Pin 14: +4.93
Pin 15: +0.49
Pin 16: 0.00
Just checked it again. Amp is intermittently powering up now.
Last edited:
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