Amp protects at mid volume

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Hello!

I have a mono amplifier 850 watts rms with an issue. This amp protects at mid volume. Capacitors are new but have some repair in driver board and some external circuit.

I wondered why i'm measuring -38V on Pin 3 or Pin 4 of the driver board terminal. I don't know if this related on this issue.

This amp is generic or china made amp, pls see attach image.

Please help...

Thanks,
 

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'Mid volume' doesn't tell us much. Does the shutdown occur at precisely the same output voltage regardless the load (no load or toughest rated load, shutdown at same output voltage?


First I thought it protects due to lower supply voltage but it doesn't. I've tried 10Volts supply and the amp still good at lower volume.
I think the amp protects at the same amount of output voltage.
 
I think I know basically what this is. The DB Drive amps use something similar but use a different modulator board.

If you adjust the potentiometer on the modulator board, does that adjust the DC offset at the speaker terminals? yes the dc offset changes if you adjust the potentiometer.

Does the amp go into protect with no load?

The amp didn't go to protect mode if no load.

The optocoupler supply comes from one 7805 regulator.
 
There are 3 over-current shunt resistor circuits from what I can tell, I'd jump each shunt resistor to see which one is causing the shutdown and then trace the circuit back from it to see if you can find the fault.

May I know what is the size of this resistor? Are these resistors place series with the rail supplies? I've seen 3, 2watts resistors connected to rail supply and goes to driver board.

Thank you...
 
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