Controller isn't turning on, but does try to charge, but doesn't

Hi, so I got this non-working PS4 V2 controller, because I had another PS4 V2 controller with some issues and and wanted to try to make one working controller.

I need the board from the non-working one, so I hope maybe some of you might give me some ideas at what to try.

Things I noticed about it: most likely, it's a botched repair. As a screw insert was broken, the charging board wasn't right for the controller board and there was a bunch of flux.

Luckily, I had a new charging board that is the same model - JDM-055 (I think?). I put that in, a new battery and no luck. Connecting it to the PS4 itself, it doesn't even detect it. Trying to charge it with a charging brick, orange light doesn't come up, but the usb tester does show that it tries to take 0.04-0.14A and then goes back to zero and jumps around like that. I gave the controller board a good cleaning with rubbing alcohol, tries using the restart button, but no luck.

Maybe you have any ideas?