Yes it ties to a 6.8K resistor. The voltage on the driver side seems more stable, if that makes any sense. If I try to apply a full 12VDC to B+ the amp starts to draw excessive current. I only have one output fet per bank populated.
I removed the output fets and now unable to reproduce the negative voltage on that pin.
Changing the op-amp should not have done that. If the op-amp was not defective, you should have seen the same problem, not a completely new problem. Are you sure that you don't have a bad solder connection or a solder bridge?
Back to the original question, voltage on the 6.8K. Reads 0.00 towards the driver board and .25Vdc on the opposite end.
I swapped the driver board with another amp I have here. With protection disabled I see the lower part of the sine clip before the upper. I also noticed U16 (TL072) pin1 has the signal riding on +5Vdc.