Working on classic electromechanical (EM) pinball machines is always an adventure, but sometimes the biggest issue isn’t age—it’s previous “repairs.” This week, I took on a Bally Wizard repair that had a very strange bonus unit issue..

The bonus stepper unit was completely jammed up. It would start counting at 5,000 points, max out abruptly at 10,000, and refuse to reset to zero when the ball drained. When I took the mechanical unit apart, I discovered something unbelievable: the copper wiper blades (the rotating contacts) had been installed completely backwards by someone in the past! This meant the contacts were never reading the correct positions on the disc.

But that wasn’t the worst part. Digging deeper, I found a series of jumper wires that made absolutely no sense. These bypass wires led nowhere and, because they were wired backwards, were dangerously close to melting one of the main coils.

The Fix:

I had to undo the entire mess. I removed the dangerous hack wiring and restored the circuit to its factory state. Then, I rebuilt the stepper unit, installing the copper wipers on the correct side and at the right angle. After a good clean and lubrication, the unit now resets perfectly to zero and counts bonuses with the mechanical precision you expect from a classic Bally. Another machine saved from an electrical disaster!

This is the bonus stepper unit with the wipers in the correct position.

If your pinball machine needs a service, contact me here