I have a Mappy board where player 1 start doesn't work, but 2 plater start does work. If I short ground to the start 1 pin on the edge connector nothing happens. Is there anything trivial I should try before tracing the signal through the board?
If its not working when you short the P2 edge connector pin then its a board problem. It probably runs through a resistor pack or a resistor and then capacitor on board. Check those for physical damage first. Check the schematics and see which IC handles the inputs.