Peavey Prosys 112 - Has hum and low signal output - Need Advise

[Enzo]

Yep, that lack of power supplies to the IC is why it isn't doing anything.

Remember, the two voltage regulators are ONLY for the preamp supplies. They are wired directly to the cable pins to the preamp. The ICs on the power amp have their own 15v supplies from the power amp circuit, CR4 CR5. WHich makes me ask, are the +/-45v rails present? Those 15v supplies derive from the 45v supplies.

Do check resistance to ground from pins 4 and 8, but also check resistance from pin 4 to pin 8 directly. A shorted IC might not even have a ground connection.

[CoopDaKill]

Resistance of U1 is
Pin 4 / 2.8M
Pin 8 / 2.9M
Pin 4 to pin 8 / 1M to 3k

I rechecked the power amp voltages and all are good. So, I injected audio signal directly into the poweramp board, hooked up the speaker of the unit, and got good clear sound. So, this leads me back to the preamp board. ???

[The Dude]

Something is funky here. First you said no supply to IC1. Then, the power amp works. This can't be. Did you do something to restore supply voltage to the IC? Or maybe did you inject signal after the IC? Can you clarify? Do you now have supply voltages on pins 4 & 8 of the IC?

[CoopDaKill]

Tell me about it! I have 15v on pins 4 and 8. And the power amp passed good signal. Thinking about taking the shotgun to it! Lol