On any pin, always best to start off with nothing connected. Verify your Secondary winding outputs first, then check out the power supply physically. Inspect caps for leakage and age, test diodes and rectifiers, look for cold/bad solder joints. Then fuse by fuse/section by section plug in connectors and go through the psu until all of your voltages are squared away. At that point, do the same with the rst of the boards (diodes, cap, physical inspection and solder joints) and start connecting power to boards, starting with the mpu. If you can get the mpu to boot, then you can inspect the playfield itself for missing diodes, resistors, caps, loose wires, damage. Connect the playfield last once you have verified all the boards are reading proper voltages and don'r blow fuses. Reason being that you want to isolate playfield issues from board issues. Hope that helps.