Often people will contact me about reset issues with Williams pinball machines, primarily associated with the WPC era from the early 1990’s. I presume they do a little searching around the internet and come to the conclusion this is a real common problem, solved by replacing BR2 (bridge rectifier) and C5 (filter capacitor).
What happens is that many people will attempt to shotgun these parts (shotgun means to replace without knowing if they are in fact defective). Some of these people will have limited de-soldering experience, and end up damaging their Power/Driver board.
In my professional experience (30+ years), my opinion is that there is no common Williams reset problem. Reset issues can occur in all solid state pinball machines and all brands, and it can be caused by many different things, most of them related to the power chain. When the voltage drops below a threshold, the circuitry is designed to reset the pinball machine.
I’m all for people repairing their own machines, and I’m happy to help and teach them. But shotgunning parts on a printed circuit board is usually not good for the board. The heat and physical stress from de-soldering a part will usually lift the copper pads or traces from the fiberglass, or pull out the metal plating that is inside the hole that the component pin is going through.
If you have a reset problem, get the correct diagnosis before swapping out parts.
With my oscilloscope, I can check BR2/C5 in about 60 seconds. It’s immediately apparent when the bridge rectifier is defective; the pulsating DC will only have every other pulse showing.
Here are some reset issues I’ve worked on, and what the problem ended up being:
- Independence Day (Sega): This is one of the very few that ended up being the bridge rectifier. In the case of Sega, it’s called BRDG21.
- White Water (Williams): The owner was having a reset issue and had read about BR2 being the culprit. He wanted me to verify that BR2 was defective. It turned out that it had already been replaced, along with C5. While I was at his home, the basement lights dimmed when the furnace blower switched on. I suspected an issue with the house wiring (it was an old house). He turned on other appliances and the line voltage reading dipped down to about 105 volts. I suggested he try a uninterruptable power supply (UPS), normally used for computers, to handle these brownouts.
- Black Knight (Williams): The basement of this home was wired with ground fault interrupters (GFI) after a flood. Most pinball machines won’t work with a GFI.
- Star Trek: The Next Generation (Williams): Reset issues on this machine were only in the first few minutes of power being turned on. I replaced the inrush current limiter (varistor in the power switch box).
- Starship Troopers (Sega): Resets were pretty random, but grouped together. I traced the problem back to the F23 fuse. It was loose in the fuse clips and running very hot. I tightened the fuse clips and reinstalled the fuse.
- Twilight Zone (Bally/Williams): The reset problem was caused by the power connector, where the 5 VDC leaves the Power/Driver board at J114. The insulation displacement connectors (IDC) have metal forks which pierce the insulation of the wire to make a connection with the copper inside. These connectors are problematic due to the wire working loose due to vibration and movement. I re-seated the wires into the connector and the problem was solved.
- Doctor Who (Bally/Midway): same problem as Twilight Zone above, except at connector J101, where the low voltage AC power enters the power driver board before going to BR2.
This is just a sampling, but failures of BR2 are not as common as some people think. Also, I have yet to see a case where C5 was weak or needed to be replaced.