I picked this Scorpion up a bit ago and have been going through it getting it ready to play. After doing the usual sockets, interconnect, header pins, etc. on the boards it was mostly working pretty quick. As I shopped it out I discovered issues here and there and this is one of them...

All of the drop target solenoids will fire, both in game play and test modes. After cleaning the horseshoe contacts and boards and fixing a few broken connections, all of the switches register as well. However, the 3-bank in the upper left of the playfield will not pop up when the playfield is in its down position. I can see it try, but it doesn't make it all the way, like the coil isn't strong enough, or isn't being pulsed long enough, to reset the mechanism. If the playfield is raised this one resets fine though. I also noticed that all three drop banks have the same not-quite-enough-oomph behavior in test mode only, even though the 5-bank and the other 3-bank are fine during gameplay.

I noticed this towards the end of my work session so the only troubleshooting I've done so far is to hand actuate the mechanism and verify it's free of obstruction or excessive resistance, and to swap the coil since I had a brand new one handy. Neither was effective. My next thought is to test the wiring from the boards to the mechanism to make sure there's no indication of a bad connection somewhere in that chain, and then next I'll test the transistor pair for this coil on the driver board. Think I'm on the right track? Anyone else seen this behavior from their machine?

Yeah I bought repro horseshoes and boards since I'd heard this design is awful but the stuff installed was clean enough I kept the originals for now. Bent the horseshoe tensioners out a bit and polished the contacts, and polished the board side contacts as well. The switches all register in test and gameplay, so I don't believe they're the problem (for now). Biggest problem with that area was several of the ground piggy back connections for the boards on the back set of drops were broken.

Tried some more stuff...

-Swapped power supplies since I haven't rebuilt the original from Scorpion yet, no change there, hanging around ~34V DC solenoid B+ measured at the power supply and at the coil.

-Checked wiring for both power and return from the backbox to the coil, no resistance. Reseated connectors too just to be sure. Inspected the power supply daisy chain for fatigued wires as well.

-I also had the driver board out to swap a transistor pair for a jet bumper so I did the pair for the 3-bank as well.

Also found another thread with a similar though wider spread issue: https://pinside.com/pinball/forum/topic/black-knight-solenoid-targets-not-popping-back-up/page/2

Well, I apologize for the somewhat boring conclusion. This seems to have been a mechanical issue. Having exhausted the possibilities for it to be a board or wiring problem I took another look at the mechanism itself and carefully checked each drop target. I noticed one target had slightly more drag than the others, and that went away when I pulled the switch PCB off the back. So I bent the horseshoe contact back a bit to take off some of the tension and put everything back together, tested that the friction each target had was pretty even, and now the thing works perfectly. What an obnoxiously finnicky design...

I did notice another symptom while I was testing the coil manually by jumping the drive transistor tab to ground. With power applied for a bit longer than the driver would pulse for it would raise the targets, but there was an audible hum as though it was working a lot harder than it should be needing to. Recording that just for the benefit of whoever comes upon this thread trying to chase down something similar.