I picked up a Frontier about two weeks ago, and I've gotten to the point in the repair process where the only problems left are the tiny little things that drive me insane. Case in point: The C rollover at the top of the playfield was registering twice. I tried adjusting the switch, but no luck. I did a bit of research and it sounded like a bad diode, so I replaced the diode on that switch. No change. Then I checked the switch matrix and replaced every single diode in the same row and column (including all three tilt diodes). Now the switch started either registering three or four times on a single hit, or more often, not registering at all on a hit. I texted a buddy of mine who knows more about pinball than I do, and he suggested a bad capacitor on the rollover. I checked under the playfield, and none of the three rollover switches had caps. Aha! I ordered a bunch of caps from Great Plains Electronics today, but I'm impatient, so I pulled the cap off the grizzly target standup and soldered it to the the C rollover switch. I fired up the game... and now the switch consistently registers, but it's back to registering twice. My theories are as follows:

1. The cap on the grizzly target that I pulled is bad, but this seems unlikely.
2. The rollover switch itself is bad, but I can't find a replacement at any of my usual suppliers (suggestions requested!)

Any advice would be greatly appreciated. I've dropped a solid five hours into this issue and I'm tearing my hair out. Thanks in advance!

I've adjusted it to the best of my abilities, which is part of why I'm leaning toward the "bad switch" hypothesis.

Thanks for the suggestions, everyone! This gives me a good starting point. I'll post an update when I crack this one.

I'm thinking this might be the problem. I fiddled with adjusting the switch some more last night, and I got it to a point where it works reliably about 90 percent of the time. I'm going to check out the wire form. Thanks!