3DS popping sound (not the usual fixes)

Hello. so before you tell me it is the speaker cable, the camera cable or the screen or anything else, i tried another motherboard on this setup and it worked perfectly, and i have a new ribbon cable and a new screen, and nothing worked for this board. so what i am asking, is what components should i check to see if there is a short somewhere that is not letting the upper screen backlight get its power and causing this problem?

thanks