Quote:

And why specifically the negative part of the waveform is distorted, but NOT the positive..?


Bipolar voltage running the opamps.

The negative side isn't up to snuff.

Suspect a bad opamp here, since the other outputs are still healthy.

This is a job for a competent electronics service technician, as there are other things that could cause this, associated components to the output opamp for that output such as resistors, possibly capacitor, but the first thing to suspect is the output opamp, likely has a bad internal junction on the negative-going side.


--Mac
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