This section of Pinwiki suggests there is probably a pre-driver transistor you should check: https://www.pinwiki.com/wiki/index.php/Williams_System_9_-_11#Special_solenoid_problems

I was helping try to diagnose this one with Dan, last week.

I tested the predriver and it reads just as all the other working ones around it. Getting the .4 - .7 reading.
Diode on the switch stack is testing good, as well. Cap does not read shorted, either.
The game killed 2 tip102s that I swapped in that night.
I'm thinking PIA, but didn't have any on hand to swap out.

Are the pops in the “special solenoid” section of the board?
If so they can take out the chips that are in that section.

Yes, the pops and slings are in the special solenoid section on this game.

I must be missing something obvious because if the machine is off and the plunger is still pulled in the solenoid, this suggests you have a mechanical problem.