This amp is mostly working. All 4 channels are operating, except Channel 3 is much louder than the other 3 channels. Pre-amp signal amplitude is the same for all 4x channels, but output at terminals for CH3 is about twice as loud as CH1/2/4. Otherwise the amp reaches clipping points and has passed most tests other than CH3 being increased beyond CH1/2/4. All 4 channels clip at the same amplitude, just CH3 clips much sooner than the others - IE with lower input signal.
I think there is something going on with the feedback section of this amp, but not really sure where to look exactly?
I think there is something going on with the feedback section of this amp, but not really sure where to look exactly?
There is typically a voltage divider that goes from the speaker output (near the output transistors) to ground via an electrolytic capacitor. The center-tap of the resistors goes to the inverting input of the differential amplifier. I'd suspect that one of the resistors is out of tolerance.