Hey! I finally opened up Mario Bros. Inside was relatively clean. I pulled the PCB out of it’s cage, and this is what I found:

By the look of those batteries, I’d guess they were the ones that came with the game back in ‘83. You can see the corrosion all around the components to the right of the batteries. I believe that dark stuff on the edge of the board is also corrosion underneath the coating they covered the ground trace with.

Checkout the corrosion on the back side:

I got lucky that the corrosion didn’t seem to spread beyond what you see in those pics.

The batteries are only used to save bookeeping info for operators. Seeing as this Mario Bros. is not likely to be put in a real arcade anytime soon I figured it would be best to just remove them. I removed the batteries and holder and cleaned up the area with a small wire brush. Then I went over it with a 50/50 solution of white vinegar and water to neutralize the acid and keep the corrosion from coming back. After that, I went over it with some 91% rubbing alcohol. Here it is after all that was done:

Along that bottom edge, I had to sand it to get rid of the corrosion that was underneath the coating. I also had to replace a capacitor – C1. The corrosion ate right through one of it’s legs.

I put it all back together and it still worked (phew!). Here are a few pics showing it in its new location in our game room.