TK, photos from user calibration are very strange. I'm wonder, why it's not return fail immediately. Did you resolder connectors? If scope is working well, problem probably is in signal generator used for calibration. Check U33, U47 and stuff around it including PWM5V supply rail from U30. It's wired that it is in both channels... So check also 2 components on top side of main PCB, on the right from CH1 front end (capacitor and inductor). They are connecting both channels with BLT PCB. entry point of this connection in analog frontend it's via 390ohm resistor, A7 (sot23) double diode, 47X resistor to pin 1 of U34/U39. Maybe some capacitor on the way fail to open, and PWM signal is visible instead of DC. If here is everything okej I think that problem is in BLT board - bad solder points under BGA or damage inside IC's. Unfortunately my logic analyzer is too slow to capture digital communication while user calibration. I don't have more ideas to solve it.