One of the most common problems on pinball machines is people forgetting to replace their batteries (located on one of the boards in the backbox of the machine).
The batteries then leak over time and eat away at the board and components, causing all sorts of nasty issues.
The best way to overcome this problem is to install a remotely mounted battery pack. This is a quite easy procedure if you have basic soldering skills. I will put a video up soon showing how to complete this essential modification.