(Topic ID: 280994)

Williams EM Transformer Cut-off?

By schudel5

3 years ago

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Latest reply 3 years ago by schudel5
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Fun-Fest Williams, 1973

I have a Williams Fun-Fest with a 15-A-6771 transformer. I was playing a 4 player game when the power just died in the middle of a game. I thought it was a blown main fuse but it was fine. I put the fuse back in and turned the game on. The transformer does seem very warm...maybe even bordering on hot. I can only put my hand on the metal laminations for about 5 seconds. I put a clamp-on ammeter on the power into the transformer and it's only pulling 2-3A AC. It is NOT set on high tap either FWIW.

My question is this. Do these transformers have a thermal cut-off inside? I'm wondering if that's what caused the machine to shut off or if it was something else completely.

Did you check the fuse near the transformer? Transformer problems are pretty rare overall.

If it's a factory transformer, there is no thermal cut-off built into the transformer. It's normal for these transformers to run fairly hot. The current draw doesn't seem out of whack, although it does sound a bit higher than I would expect.

There is a more common reason for the problem you are seeing. If there is a fried coil in your game - such as a pop bumper coil or a score unit coil (maybe on some player other than player 1) then what can happen is that the game will start normally and will seem fine until that coil gets energized. The resulting short circuit in the 25 VAC circuit will cause the lock relay to release, and the game will shut off. This will happen fast enough to prevent the 25 VAC fuse from blowing, although it will eventually blow if you repeat this shorting process enough times.

As currieddog points out, the same symptom can happen if the 25 VAC fuse is loose in the fuse holder - as soon as the fuse loses contact, the lock relay drops open and the game shuts off.

- TimMe

Yes a factory transformer. I compared it to my Grand Prix and it does run hotter than that. The 2-3A was peak amperages when operating the game with flippers, swing motor and pops going off. At idle it's 1.2A.

So while checking fuses, fuse holders, lock relay and game over relay, I would unplug the game and plug it back in between doing the checks. Interestingly it would sometimes power up and other times it wouldn't. While it was powered on I went to touch the plug and it shut off. It seems I have a bad power cord! I plugged it in with the switch on and I could hear the transformer hum go on and off as I wiggled the cord at the plug.

That's all it was...bad cord. Easy fix. Thanks for the insight on the transformer.

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