Machine: Williams Twilight Zone (1993) Location: South Bristol (On-site Service) Issue: Random Game Resets / Rebooting during play
It is arguably the most common issue on 90s Williams/Bally (WPC) pinball machines, but it is also the most frustrating. Today, I traveled down to South of Bristol for a service call on a Twilight Zone that was suffering from “random resets.”
For those unfamiliar with the problem: you are in the middle of a great ball, you hit both flippers at the same time, and suddenly the game goes dark and reboots as if you just turned it on. This is caused by the 5V logic power rail dipping below the threshold required for the CPU to stay active.
The Diagnosis Since this was an on-site repair at the client’s home, accurate diagnosis is key to avoiding taking boards back to the workshop. When a WPC game resets, many technicians immediately rush to replace the Bridge Rectifiers (BR2) or the large filter capacitors. While those are often the cause, they are not the only cause.
In this specific case, I dug a little deeper into the Power Driver Board.
The Fix: The C4 Capacitor Upon inspection, I found that the bridge rectifiers were actually functioning well. However, there is a small component that often gets overlooked in these repair scenarios: the C4 Capacitor.
The C4 cap sits on the 5V regulator circuit. If this small component fails or dries out (which is common after 30 years), the voltage regulator becomes unstable, leading to those annoying resets.
Work Performed:
- Replaced C4 Capacitor: Swapped the failing component for a high-quality modern replacement right there on site.
- Replaced C2 Capacitor: I also replaced C2 as a preventative measure, as this can also contribute to power filtering issues.
- Connector Inspection: I checked the usual suspects (J101 and J114 connectors), which are notorious for burning out on Twilight Zone. Surprisingly, in this machine, they were in excellent condition and required no re-pinning.
The Result After swapping the capacitors, the 5V line is now rock solid. I play-tested the game extensively (see the video below), hitting both flippers repeatedly during multiball modes. The game held steady with zero resets.
Another Twilight Zone saved from the dreaded “reset loop”—and the client didn’t even have to move the machine from their games room.
Is your Williams pinball machine resetting in the middle of a game? Contact Lyon Pinball. We provide on-site repair services across the UK, including Bristol, Cardiff, and surrounding areas.