Ran into this gremlin and haven't been able to solve it on my own. Lower Pop on Space Shuttle is currently not working, and it's my favorite of all the pops. The game is really boring without it. Everything else is currently working.

Here's the current rundown. This is a Special Solenoid, which means it has it's own special uniqueness. Bottom switch is fine (switch 27, shows up in the Matrix and all that) but the top switch does not fire the pop.

I've tested a lot of stuff. Here's the most notable items.
Grounded Q81 - Pop Fires
Grounded 1J18 pin 4 - Does Not Fire
Grounded single lug under playfield - Pop fires

So that leads me to believe the problem is at U7. So, I grabbed the ol' Logic Probe and just ended up confusing myself. I tested all the pins on the working switches on U6 and came to the same conclusion: one pin high and output high, other side goes high when the switch is depressed and output goes low. Jet or kicker fires, rinse and repeat.

U7 was socketed and I tried another one I had lying around and came up with the same results twice.
Q77 - Right Kicker works however: one pin high (6) and output high (4), other side stays low (5) when switch is depressed, output stays high but Kicker fires.
Q81 - Non-working pop: one pin high (11) and output high (13), other side goes high (12) when switch is depressed but output (beep) goes away.

So, where do I go from here?

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Help? If grounding 1J18 pin 4 does not fire the coil, where do I look? I've search through other thread on Special Solenoid switches and haven't seen the resolution of that issue.

Well, I guess I fixed this. Missing continuity from one leg of Q80 to one leg of Q81. Still doesn't fire like the other pops when manually engaging in switch test mode but works in game. I'll take the win.