This seems eerily similar to a fault I had on a previous amp, but somehow different.
This current amp is not producing equal PWM signal to the output stage, bridging pins 1 & 2 of U513 does make close to equal pulses but not quite equal. With pins 1 & 2 open, the voltage seen at the LM319 pin 4 is too high to allow proper oscillation at around 3.3v where I would expect it to be around 2.2 or so (it needs to be right in the middle of the triangle wave seen at pin 5 during idle conditions).
This board version doesn’t seem to have an offset pot it only has a clip pot, so I can’t do some of the testing shown in the attached thread. U503 and U513 are already replaced with no change, the amp showed up with a smoked pair of output filter caps which were also replaced (a pair of .22’s near one of the chokes, can’t see the designator anymore but they go from either output leg to ground). Question is, where is this extra voltage coming from?
This current amp is not producing equal PWM signal to the output stage, bridging pins 1 & 2 of U513 does make close to equal pulses but not quite equal. With pins 1 & 2 open, the voltage seen at the LM319 pin 4 is too high to allow proper oscillation at around 3.3v where I would expect it to be around 2.2 or so (it needs to be right in the middle of the triangle wave seen at pin 5 during idle conditions).
This board version doesn’t seem to have an offset pot it only has a clip pot, so I can’t do some of the testing shown in the attached thread. U503 and U513 are already replaced with no change, the amp showed up with a smoked pair of output filter caps which were also replaced (a pair of .22’s near one of the chokes, can’t see the designator anymore but they go from either output leg to ground). Question is, where is this extra voltage coming from?