Diagnosing and repairing a Williams WPC Pinball Opto Board: Junk Yard

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Repairing and refurbishing pinball machines is our specialty, but we also buy, sell, and trade pins. Need a part? If we don't have it, we can probably get it. We are a veteran-owned, fully licensed and fully insured Tennessee Small Business.
East Tennessee Pinball
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Knoxville, TN 37922

[@Jesselovespinball]

Those problems can really drive you crazy ! You didn’t give in and order the replacement board which is commendable . Especially because it was only 100 bucks for the replacement. I had a similar problem on Twilight Zone awhile back with optos. I ended up looking up the chip breakdown and using logic probe to see if I was getting all the outputs and inputs . The chip tested okay just like yours but when I checked each output I found the smoking gun . Good job on not giving up on it That’s what makes us better troubleshooters !

[@ETPinball]

Thanks. If I had had the game at my shop I probably would have swapped out the chip much earlier, even with the good test. Note to self, (bring more stuff with you onsite!...LOL)

[@michaelkatz2289]

Lots of work to get that one solved. Frustrating when the testing device gives a false positive In hindsight, was there a test you could have done to know this was the bad chip? . Nice video

[@ETPinball]

Maybe if I had a better chip tester?? But I don't believe I have ever had a false positive from this one before. It did cause me some headaches...LOL!

[@mrfuzzcat]

Thanks for the thorough follow up and documentation of solving this problem. The LM339’s seem to be a common failure point on this generation of opto boards.