A common probem with both pinball and video games is the situation with battery backup.
What happens is your battery (that is hiding somewhere in the game) gives up the ghost, and unfortunatly, as it dies, leaks out an alkaline: Potassium Hydroxide. This is a corrosive base, much like lye. The way to neutralize the leakage, after removing the battery, is to wash the affected area with a solution containing a 50/50 mixture of (white) vinegar and pure water. Scrub carefully with a good toothbrush (teethbrush?), and then rinse with pure water and force dry with a hairdryer.

You should consider replacing any IC sockets that were near the battery or that you see any signs of corrosion-usually a white residue near or under the IC socket. Also the components that are near the battery must be examined for signs of corrosion on the leads. The corrosion can etch into the interior of the plastic body of the electronic components and hence cause destruction, months or years later.

Now, if you have saved your game board you will want to replace the battery and we recommend one of two solutions.

If the game is actively used, then the original Ni-Cad battery will work fine, as it will be kept charged.

If the game is to be used on a more casual basis, then get a battery holder that will equal the original voltage when stocked with AA batteries, and extend the wires so the batteries can sit on the base of the area where the board is. Then seal the battery assembly in a "Zip-Lock" style bag so if the batteries leak the vapours and liquid will be confined to the bag!

You will need to isolate the battery assembly from the origianl charging circuit by the use of an isolation diode (1N4002). The ground wire of the battery assembly goes to the original ground for the battery and the positive wire will first be connected to the non-banded end of the isolation diode, then the banded end of the diode can be soldered to the original positive point for the battery.