Had time to look at this boy more closely today.

I've washed the board completely over again, and now it's really shiny clean - unfortunately no luck with the problem.

So I've decided to do a few measures - I don't know anything about how this thing works or what are the best places to look for voltages, but I tried anyway.

The AC power supply is giving out a nice 23,6V stable as a rock. I've analyzed the group of 7 capacitors near the battery connector: the top two and the two on the left have voltages rising and falling between 6V and 10V, the two on the right between 5,5V and 6,5V, and the one on the bottom between 7V and 11V.

I also noticed that the two capacitors ranging between 5,5V and 6,5V seems to get a lot hotter to touch than the others.

Where should I look for the voltage rails? Or the resistance to ground? Is there some known schematics for this board?

Thanks!