pin 6 and 7 on the game board or check it at the connector there on the game board
that picture shows a problem with the fuse holder there and all those wires could be gathered up and a few wire ties to neaten up the area
is that a burned out fuse holder under the fuse holder floating there in space or no
negative/black lead of the multimeter on ground and the red poking in the connector pin 6 and 7 with the multimeter set on DC (not ac with the wavy line)
follow pin 6/7 wire back to the power supply to test it there.
the point of testing the output of the power supply both on the game board and at the PS itself is to detect any voltage drops along the way there.
sometimes a weak pin inside the connector can inhibit electron flow and cause all kinds of wonky problems
if this were my project, I would replace that big blue capacitor IMMEDIATELY
you can get them from bob Roberts. that could be your problem right there. those big blue capacitors filter the +5 volts and as they dry up can leak ac and cause all kinds of trouble including your problem