Thanks for the rec. What's the best method to check power? Any video guide you could point me too?
The way to check power is to get a DMM, put it in DC volts mode. Power the cabinet on, put the red lead on any +5V test point on the game board, and the black lead on any GND test point on the game board.
You want the DMM to read 5.00V. If it's not exactly 5.00V, turn the pot on the AR board (the smaller 8" board with the huge heatsink on it) until the DMM reads 5.00V.
This may not fix the issue, but it's the first step in troubleshooting any game.
Do the above and report back here, namely what the voltage was before you adjusted it.
Also get yourself the following two things: A fiberglass pen, and a can of DeOxit. Links:
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Remove the game board, and scrub the edge connector fingers with the brush so they're shiny. (Do it outside, not on the kitchen table, as the fiberglass pen makes a mess.) Wipe the fingers clean with some acetone or isopropyl alcohol and Qtips until they are clean, then apply some DeOxit to them. Also DeOxit every connector in the cabinet, anything with plugs and pins. Then check and adjust the 5V on the game board again, and tweak it if needed.
These are basic things you should do to every game, to clean all of the connections that have 40 years of crap on them. Do it to any new-to-you game. If it doesn't fix immediate problems (which it can) it will prevent a lot of others.