DWM3640 distortion at input

[NadaD]

Got amplifier which were repaired unsuccessfully before.
What is done:
* got +/- rails working
* no output fets installed
* output driver card is installed in header pins for easier troubleshoot
* no low side gate drive switching for outputs when signal is driven in
* +15 and +/-5V at output driver card are present


I checked signal when driver card is out of the board and got great looking signal.
But right after i put back output driver card, the same spot (driver card input pin) where signal was good, now looks like in picture.
Does someone have hint where to look, what cause this issue only when output card is installed?

 

[Perry Babin]

Does it improve if you connect a 10k resistor across pins 1 and 2 of the TL072 on the driver board?

With the 10k resistor in place, do you have a sinewave out of the TL072?

 

[NadaD]

Issue was that someone before was replaced R8 with 10K. Have no idea why. Before i didnt have square output at lm211
Replaced with 100k and all working fine.