Quoted from KokoNono:
Let me know if this will suffice...
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It's hard to tell with the flash, but the connectors in the brackets look discolored to me. All of them would have been in the line of fire of a leaking battery from the old board. Basically just look for any hint of crud in the metal connectors These are the two connectors to look closely at - the left one is the column drive for the switch matrix (coin door closed switch is wire 2), the right one is the row (coin door closed is wire 2). Where they intersect on the matrix is the switch in question.
These are press-fit connectors. The wires are just squeezed between two metal blades that cut the insulation when they're made. On top of the connectors, that thing is a cap. Try popping that off and looking at the area where the wires make contact with the two metal blades of the connector, too.
Also, when it happens, does it come on, then go away immediately, or does it stay on for a while?