7in5_V2: Booster Soft Start: Driving strength of phase C1 no longer accepts strength higher than 4 (stuck in "e-Paper Busy")

[vaharoni]

I connected a recently purchased 7in5_V2 (075BN-T7 2023102404) to a Raspberry Pi 3 B+. It worked great for a day, then refused to turn on and show any images due to the issue:

DEBUG:waveshare_epd.epd2in7_V2:e-Paper busy

After debugging, I noticed that if I sent to the Booster (BTST) the sequence 0x27, 0x27, 0x18, 0x17 like in fast init, it no longer got stuck in busy mode. However, the images appeared "washed out". When I tried sending in the 3rd byte anything higher than 011b (strength 4) in BT_PHC1[5:3] (Driving strength of phase C1 per page 30 of the specs), it wouldn't start and show the "e-Paper busy" message forever (adding delay in the while loop like others reported did not work). So 0x17, 0x17, 0x20, 0x17 for example would get stuck at e-Paper busy (the normal init BTST sequence in the example code is 0x17, 0x17, 0x28, 0x17).

At some point after various attempts tweaking the BTST sequence, even when using 0x27, 0x27, 0x18, 0x17 the images started degrading, and white lines started appearing on the display. I am unable to make them go away anymore (see image attached).

Is the device damaged? Or is there an initialization sequence I can try to make it work?