Hi Ozan,
Have narrowed it down to the level amps on Sheets 1-4. So yes, the levels on TP1402 etc are changing along with the trace drift.
From a cold switch-on, the level on pin 3 of U943, as an example, (the OFFSET1 signal) starts off high and slowly drops down to zero. The supplies are stable, so it seems the output from the multiplexer on Sheet 18 (U932) is causing the problem, which doesn't make a lot of sense really.
I know you said to check TP912, but this is a multiplexed signal so not easy to correlate with the level used to set OFFSET1.
Any ideas?
RJ