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Question from Jay: I was watching your JAMMA Wiring video and I have a question. Where does the ground wire at pins 28/56 usually go to/come from? I measured on the PCB in my machine and it was putting off +12V. I followed the wire coming from pin 56 to a distribution board, where it was on top of the ground wire going to pin 1 on the PCB. Matched up with these wires were the wire going from the common on the power supply and a wire coming from the lights on the coin door putting out +12V. I left the wire coming from the PS matched up with the wire going to pin 1 on the PCB, but I am not sure about the other wires. I just don’t know what to do with the ground wire coming from the PCB and the wire coming from the coin door lights.
Thank you for any advice, I have found your videos really useful.
Jay
1 answer
Response from Jonathan: Jay,
It sounds like they just added some additional ground wires to those lines so they could run them wherever they needed them. The coin door lights should have 2 wires going to them: one that’s ground and one that’s carrying +12 VDC. It needs both of these wires in order to light the bulb. If you are checking both wires with your multimeter when you’re testing the bulb then you should be getting the +12 VDC that you are describing.
The best way to check grounds is to use the continuity test on your multimeter to make sure they are all connected to the ground pin on your power supply. We talk a little about continuity in our post on Checking Fuses With A Multimeter. As long as all of your ground wires have continuity with the ground pin on your power supply you should be fine. If you want to make sure they are not carrying the +12 VDC then you can use the continuity test the same way by placing one probe on your +12 VDC pin on your power supply and the other on the wire you want to check.
Hope that helps. Thank you for your question and good luck with your repair.
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