The input to pin 1 is likely causing the problem. Unfortunately, several circuits combine to drive that pin.
In the attached diagram (which should be vaguely similar to your amp), you can see R138 (you'll have to find the corresponding component in your amp) drives all circuits to pin 1. If removed, it would allow the amp to power up but would only be safe for a few seconds because you would lose regulation.
Removing the resistor corresponding to R168 would leave regulation active and disable some of the protection circuits.
These amps also have an over-current protection for the regulators. They parallel the base and emitter of a transistor across a 1 ohm resistor. Defective components in this circuit can make the regulated output malfunction. Checking the resistance from the positive supply of the op-amps to the non-bridging speaker terminals may show a low resistance short/leak.
In the attached diagram (which should be vaguely similar to your amp), you can see R138 (you'll have to find the corresponding component in your amp) drives all circuits to pin 1. If removed, it would allow the amp to power up but would only be safe for a few seconds because you would lose regulation.
Removing the resistor corresponding to R168 would leave regulation active and disable some of the protection circuits.
These amps also have an over-current protection for the regulators. They parallel the base and emitter of a transistor across a 1 ohm resistor. Defective components in this circuit can make the regulated output malfunction. Checking the resistance from the positive supply of the op-amps to the non-bridging speaker terminals may show a low resistance short/leak.
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Could the ceramic driver cards cause this problem ?
I'm only wondering since I removed one and now I get both positive and negative 15 volts on opamps
I'm only wondering since I removed one and now I get both positive and negative 15 volts on opamps
It's possible, especially if the card has a defect that's causing an over-current fault.
Don't solder anything on that ceramic board unless you have a very good reason to do so.
Don't solder anything on that ceramic board unless you have a very good reason to do so.
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