Here is the setup:

Only one set of the three sets of white flasher bulbs was working on my High Speed, so I figured that it was a wiring issue. Then I learned that those bulbs are actually in series, so I replaced the bulbs, and they're all working. Yay!

I play a few games to enjoy the working bulbs, and then suddenly the upper right flipper is super weak - as though only the low power part of the coil works. I check the EOS, but it looks fine (though the upper right flipper only has one switch, while the lower flippers have two).

Based on another flipper issue I had with a different game recently, I'm thinking this might be a diode (but, I haven't done a ton of repair yet, so it's just a guess). The diode seems to measure differently than the ones on other coils, so I replace it. Still weak. Also, I should note this is a flipper that I rebuilt a few weeks ago (didn't replace the coil or the bushing though).

I do some googling and see a picture of the upper right flipper wiring. Then I look at mine more carefully. Sure enough, the wires coming from the EOS switch are reversed - attached to the wrong lugs on the coil. I switch them to the correct position and fire up the game. The flipper is still weak for the first couple of flips, but then suddenly comes to life - flipping hard as expected.

Can someone explain what happened exactly? How could it have ever worked if the wires were backwards? Did changing the bulbs have an impact? Just trying to learn - thanks!

Thanks. I did check that during all this.

It's not actually that I need help, everything works great...I was just hoping someone could explain why this all happened. How could the flipper have been working fine for months with the coil wired incorrectly? And suddenly stop working?

Just to follow up...

Someone more experienced than me diagnosed this correctly in person - the EOS was occasionally arcing. Another clue was that when entering high score initials, the right flipper button was *really* inconsistent...like only advanced the letter 20% of the time.

Mine are crusty and pitted also...maybe I'll replace them. Since they work now, will it end up being any different? I never sense any unreliability (now that the upper flipper is no longer arcing).