Audio amplifier - DC on output


Joined Jun 4, 2014
C103 and C106 voltages?
What's the history? One day it was working then next day it had this fault?
Working correctly, then stored for a long while, then it has this fault?


Joined Nov 13, 2015
Yes, I have power on pin 4.
U101 Pin 2 detects an excess offset. It has a negative threshold of -0.12 volts and a positive threshold of 0.54 volts. And there are dividers from each channel into that pin, so that -25 mV should not trigger a fault. What voltage do you measure directly on U101 pin 2?

Now pin 4.... What voltage do you measure at U101 pin 4? Pin 4 should be no less that +0.9 volts, and no more than +10 volts.

Thread Starter


Joined Feb 3, 2021
I think problem is with different grounds from two symetric power supplies. I found that uPC is connected to Vcc, but ground from (V). So voltage on pin 2 is -45V.


Joined Nov 13, 2015
The uPC should be connected to system ground. It is powered by it's own diode and filter cap from the power transformer secondary. How have you got the power supply configured? I wasn't able to find anything on this online other than the schematic you posted - are you working from any kind of instructions?