Did you replace the correct transistors for that solenoid as shown in the schematic for your game? If you replaced the driver and pre-diver transistors for the solenoid and it still locks on during start up, you need to look 'upstream' and test the buffer chip that controls the transistors (going by memory here). That could be checked by a logic probe. If you decide to just replace it without testing, it is a relatively cheap chip. But the damage may go even further upstream to the PIA chip, so again a logic probe would help. Circuit board soldering skills will most probably be needed.

I assume you checked for short circuits to wiring when looking over the solenoid and the boards.

This kind of repair has been covered many many times here, just search on "locked on solenoid" or similar to get the background. Pinwiki does not have anything yet on solenoids for Williams System 3-7, so Clay's guide would help (costs money).

Varistor is a two leg little lolipop shaped component in the silver power box in the cabinet where the service outlet is. It is probably not your problem unless the whole game is now dead.

Good luck, let us know how it goes and what the final answer was.

Don C.

For $30, a logic probe is a great tool. Easy to use and it's like being able to see inside the chips and circuits!

Don C.

My logic probe is an old one I used to use a a former job- but if you search Pinside, there will undoubtedly be some recommendations. I just looked in Amazon and saw basic ones in the $30 range. Some have batteries, some are powered off the board via alligator clips. Looks like Pinsider TerryB has done a nice write up: https://pinside.com/pinball/forum/topic/terrybs-guide-to-logic-probes

Clay Harrell produced a set of repair guides that are very useful. Some, like the one you need, are not free, he would like a donation. Contact Clay thru his site: http://pinrepair.com/

Sounds like you have done a good job on the diagnosis so far, eliminating the transistors. Next most likely thing to go is the buffer or the PIA or both. Other passive components like resistors or diodes could be part of the problem, but that is less likely.

Get the logic probe, see what's up with your chips and then see if you need to buy the guide. If you look carefully at the schematics you should be able to determine which chips the signals pass through. If there is only one solenoid acting up, it's likely that it is one section in the chip related to one leg on the buffer chip (first one upstream from the pre-driver transistor.

So do some reading on Pinside and get up to speed on the theory of solenoid control, and order up a probe, you should be able to make some progress.

Don C.