On my LAH both the VUK and Knocker are locking on upon start up. These happened at separate times a few days apart (the knocker was disconnected for a few days prior to the VUK locking on).

The coils aren't melted, but I suspect the respective transistor(s) may have gone bad? I went through a good portion of the transistors looking for one or two that measured differently than the others, but was getting the same reading for the most part on all of them ( .5 on one side, 1.1 or so on the other).

The knocker didn't have a diode on it, I added one, but it continued to lock on. I have yet to check the diode on the VUK.

Looking for help on what the next step in the trouble shooting process is. If anyone knows which transistors drive these two coils that would be helpful as well.

Thanks!

Thanks! Does that make sense that it would be transistors that would be bad?

Cool - all the ones I tested last night were in the .4-.6 and around 1.1 range, hopefully I didn't test the correct ones

Will report back after checking q42 and q39 this evening.

Update - the transistor for the knocker is definitely shorted, I haven't replaced it yet, but that should solve that issue.

The transistor for the VUK is testing OK. Could the transistor still be the issue?

Both the diode on the VUK coil and VUK switch are testing OK.

Any help on next steps would be great!

Awesome - will cross my fingers that that is the issue. Appreciate the help!

I checked q4 and it too appears good. I may just shotgun replace all 3 of them and see if that helps.

Anything else I should be searching for? I'm not sure how to check the continuity on the VUK. Thanks!

Update -
Replaced both transistors and pre driver transistors for the coils.

Knocker is good!
VUK is a maybe... It isn't locking on, but when fired, will sometimes stay up. The coil isn't getting continuous power, and with a slight push the plunger goes back down. This leads me to believe something is binding, but I can't repeat it without it actually firing, and it isn't doing it consistently. I'm going to got deeper into the mech, and see if maybe the spring is the culprit? Any thoughts on what to look for?