Have you tried messing with your +5 adjustment?
You should *never* just "mess" with the +5V adjustment. Get a multimeter. Set it to measure DC voltage. First check the voltage @ the power supply. It should be in the 5V range. Then measure the voltage at the JAMMA harness, WITHOUT THE GAME BOARD PLUGGED INTO IT. It should be ~5.18V.
Clean the edge connector on the JAMMA connector with an pink (not white) eraser, or 99% alcohol with a cotton swab.
Reseat the socketed chips on the board by *gently* pulling them - just a hair - and pressing them back into their sockets. If you want to go the super extra mile, you can pull them altogether and clean the legs VERY CAREFULLY.
After verifying these voltages, and cleaning the board in the manner described above, THEN plug your board in, and measure the voltage. Measure on a chip if you can (diaganol pins to each other, make sure you don't bridge other pins!) and adjust the voltage as necessary. If there is a socket without a chip in it, this is a perfect place to verify the voltage.