I'm guessing you mean U3 not Q3?
Yes, they can and do fail in sections. This chip is really only 7 separate transistors blobbed into one package.
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I'm guessing you mean U3 not Q3?
Yes, they can and do fail in sections. This chip is really only 7 separate transistors blobbed into one package.
The diode could cause issues as could anything in that chain.
If you remove the diode the solenoid should stay OFF because R26 will bias the driver transistor OFF. That would then prove your U3 is cactus.
175v DC - some suggest even lower but one thing is for sure, the factory suggested 190V is WAY too high.
The trimmer should be 25K measured across the two outside terminals OUT OF CIRCUIT!
You likely have other problems with the regulator circuit - very common. I suggest you head over to PinWiki and have a good read - it has EVERYTHING you need to know to fix this regulator part of the board.
The centre of a pot is the wiper. As you turn it, it transitions from one outside leg to the other. Not much point measuring from the centre leg.
Yes, the transistors are likely toast.
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