(Topic ID: 312467)

Twilight Zone Electrical Anomalies

By Yakrobat

2 years ago



Topic Stats

  • 8 posts
  • 3 Pinsiders participating
  • Latest reply 1 year ago by Yakrobat
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#4 2 years ago

Here are a few items to look at:

The +5V voltage only being 4.8V seems low as when the game starts playing and drawing load, this voltage will drop further. There is a lot of information on this issue. Check out PinWiki: https://www.pinwiki.com/wiki/index.php?title=Williams_WPC

I suggest reflowing all of the connector header pins on the power driver board just to eliminate any potential cold solder joints. Look for any cold solder joints on the large filter capacitors and bridge rectifiers.

I had an opto issue on my TZ under the playfield and it ended up being a broken connector pin; it looked fine until I looked directly into the connector and saw that half the pin had broken off.

I've had problems with the ribbon cables on these older games getting flakey. I generally replace all of the ribbon cables on this vintage of games to eliminate these issues. Pinball Life sells replacement ribbon cables, just check the manual for part numbers.

Here is some music to motivate your repairs:

#7 2 years ago
Quoted from Yakrobat:

Eric_S
I am familiar with issues caused by low CPU voltage and ribbon cable problems, my Judge Dredd was a prime example. In this case, the issues present as something else entirely.
Also, while I suppose header pins are worth looking at, the game is essentially new and the pins have almost none of the stress cycles seen on a typical machine. Moreover, I suspect a header pin would more likely cause intermittent functionality, as opposed to the predictable and highly anomalous behavior seen to affect the 20V accessories.
If I were to guess, I’m going to focus on the fact that TP7 is 1.2V but jumps to 30V when flasher lamp #28 is plugged in. This circuit should be closer to 20V and the circuit has commonality with many (all?) of the non-functional components. I'm just not adroit enough to know what could cause this...

Try to isolate the 20V issue by unplugging all of the "output" connectors on the power driver board and then measure voltage. If the voltage is still low, it is probably an issue on the power driver board. If the voltage is good, then you can focus on external issues, such as items under the playfield. Most mechanisms have connectors that can be easily unplugged to further isolate and troubleshoot.

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