This is a broken amp, it didn't work when I got it, the transformer was missing. After a period of repair and destruction (I connected the power supply wrong, fried two capacitors). I installed the correct transformer and replaced the new STK043 amplifier. Since the circuit diagram was not very understandable to me, I chose the AUX input which seemed to be the easiest to repair. Finally I got the output after the AUX input. But there was a popping sound on the right channel at first, and there was a bigger popping sound when turning the volume potentiometer. I cleaned the potentiometer and the resistance value was all right. When I turned the potentiometer, the popping sound decreased, and if I didn't turn it, it almost didn't pop, but it still appeared occasionally, and I found that there was a significant bass background noise, which was not there on the other channel. I have a signal generator and an oscilloscope, just now I input a 3V sin wave, it seems that the voltage is too high? The heat sink of the chip became very hot and there was no output signal anymore. I thought I burned it, but after cooling it down, it seemed to be fine. It was a false alarm. What can I do now?
Schematic diagram in the attachment。
Schematic diagram in the attachment。