I finally found the problem !
After cleaning the logic board, replacing the capacitors on both boards and two diodes on the analog board (as suggested by @bibilit on another thread), still nothing worked. My voltage was a little bit better, but still not enough.
So I changed the CNY75GB optocoupler, and now everything works perfectly fine !
Thank you all for your help
That's absolutely insane. I definitely would have given up fore sure.
You're an inspiration Potato.
All that hard work and what it looks like now, it might actually, possibly, hopefully, with some wood-touching, power on to maybe something on screen.