Its a bit hard to see from the photos, but the black stuff is normal for any pinball.

Just take care if poking around the display whilst its on.  Most operate on high voltage and will give you a nasty shock.

I would first look for dry solder joints on the connectors.

Disconnect power, wait for a bit then remove the board.  On the underside of the molex connectors, where they are soldered to the board.  The solder will be dull grey colour if its gone dry and if you wiggle the actual connector, you may see the solder where its broken away from the tracks.