On some electromechanicals, usually Williams, the credit unit can cause a
blown fuse or cause the game to reset in the middle of a game. This
can happen when the credit wheel over rotates past zero or past the maximum
credits. This forces the zero-position switches to short against
each other or against the maximum credit switch as shown in the figure
This problem usually doesn't happen, but sometimes does because somebody
messes with the credit unit, incorrectly trying to set it for free play.
The solution to this is to make sure the limit pegs/screws on the credit
unit are in their proper positions, and if needed put something between the
switches, such as electrical tape or fishpaper insulator.