I am finishing up my Cactus Jack system 3 and want to make sure I'm getting 5 volts to the cpu board. The sound has been wonky ... Works most of the time but occasionally some individual switch sounds are missing. Sometimes it starts with a terrible scrambled "screeching" - see video below that I shot of that event!

Can some share a picture of EXACTLY where to connect my DMM on A1P1? Both positive and ground leads please ... I don't want to screw up a working game!

These are the instructions I don't quite understand . I see A1P1 but not sure which pin is which

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Check for Proper +5 volts at the CPU board.
Because the Gottlieb System3 power supply has a 500 ohm adjustable trim pot for the +5 volts, it can get out of adjustment. It is best to test for proper +5 volts at the CPU board. Note there are no test points. Use the A1P1 connector (pin1=+5, pin4=ground). The voltage should be 4.95 to 5.15 volts DC. If it is outside of that range, adjust the A2 power supply trim pot. Note this trim pot is notorious for being worn out. Replacing it with a new quality trim pot is often a good idea. If +5 volts varies a lot on a game from time to time, suspect this trim pot as the problem.

Youtube link that shows my sound issue pretty clearly. Sounds terrible until I plunge the ball

Morning bump

Mid day bump

Thanks I was able to do that and measured 5.15 volts and dial that back using the pot adjustment to 5.02 volts

Thx again