When I open it up and toy with the contacts I can get all the buttons to work at the same time, and indefinitely, by bridging the start button contact with a single piece of metal. The 3 lights will go on and stay on, and the game will keep receiving start repeatedly. I have tested this with Virtua Racing, it will start the game, go through all menus and then when the race starts it will pause and continue repeatedly. When I touch both sides of the start button contact with a multimeter it does nothing.
I don't know much about electronics, but I would like to repair this controller.
Here are pictures of the inside of the controllers.
The no continuity is expected. You would only get a beep if the button is pressed (the press happens when both sides are connected by a conductor, which in the case here is the carbon on the button membranes). It could be the contacts are just dirty and cleaning them with a q-tip and ipa is good enough. I would also lightly clean the membranes as well to make sure there is no dust or residue on them (the carbon on the button will always come off on the qtip, so just lightly clean that part).
I have already cleaned the contacts and the membranes. How would I go about tracing where the problem lies? I know there's no continuity when the button isn't pressed, but nothing happens when I bridge any of the buttons, either with the membrane or otherwise, with the exception of the start button, which then seems to trigger all the buttons continuously (judging by the leds).