I have had my Stern AC\DC Pro for about a month now, and over the last week and a half or so I have noticed the right flipper beginning to stick in the up position. Up until last night it was more of a nuisance than anything--it would get stuck for a split-second, then with a tap of the flipper button it would drop. No big deal, it didn't hurt my game much at all. However, last night, it began sticking up permanently. No amount of button pressing or smacking or shaking the cabinet would fix it.

I am still a bit of a newbie when it comes to working on machines, so I am looking for advice on this issue (from others I hear it's common). In the last ten months since I purchased my first machine, I have only had to solder a wire back on a target, that's about it, so technically this is the first truly mechanical issue I've had to deal with, per-se. Any help is greatly appreciated.

Here is what I've figured out so far:

- Going into the test menu and performing a coil test on the right flipper, it stays up after activating the coil (whereas the left flipper that is working fine falls back down after doing the coil test)
- When I go underneath the playfield and manually push the flipper mechanism with my hand, it retracts as it is supposed to (i.e., the flipper drops)
- When I trigger it with the flipper button, it often times sticks, but not 100% of the time.
- I thought maybe the right flipper leaf switch was a problem (it may be and I just haven't figured it out yet), but it looks nearly identical to the left one. I played with the contacts on it and bent them out a bit (they seemed to be slightly closer together than what I saw on the left flipper leaf switch), but that didn't really do much.
- One indication that there could be a problem with the right flipper button switch is that sometimes I won't be able to scroll right in the test menu. Other times when I'm not in the test mode, the jukebox on AC\DC has on occasion come up on its own (this is triggered by holding in the right flipper).
- My only concern with the above is, why wouldn't the flipper come down when doing the manual coil test in the diagnostics menu? The flipper button shouldn't have anything to do with that specific test. Or am I wrong?
- Solder joints all look fine, and I don't see any obvious tears in the wiring, although admittedly I didn't look that closely last night.

On a side note, I don't have a meter (I still need to buy one), so I don't have a way of checking continuity yet.

Thanks for the information so far everyone.

@PEN, which piece is the coil stop exactly? What does it look like (or is there a good guide out there that names each part of a flipper build)?

Yeah, it also seems out of the ordinary because the game isn't that old, and it was HUO prior to me owning it with fairly low plays. However, it seems like flippers sticking may be a common theme with these AC\DCs, I've got another friend locally that mentioned the same thing happening on his.

I've got some errands to run, but once I get back I'll be digging into it. Crossing my fingers it's just the gap issue.

I am having a hard time just getting the coil assembly screws out. Hm..

I attempted to get to the flipper bushing to loosen that up, but could only get to two screws. The other is blocked off and I can't get to it without removing the coil assembly.

I may have found the potential problem though. It seems like the plastic-ish elbow part of the arm is getting caught on the short piece of the end of stroke switch. See the attached photo below. I'm assuming I should be able to file down the plastic piece slightly, unless anyone has a better (wiser) idea.

flipper stuck.jpg

Ah, okay. I will try that, but what I think is happening is the plastic piece that hits the end of stroke switch is misaligned. If you look at it, it has ridges that are shaped like a bracket ( " ] "). On the left flipper it is rotated more and the long inside portion of the bracket-like notch sits flush against the metal nub. It seems because it's out of alignment, it is literally getting caught on the small tip of the EOS switch.

flipper stuck copy.png

Yep. I've been referring to the left flipper to draw comparisons with the right, but I don't know why I didn't catch that difference until now. I may have personally made it worse by beginning to mess with the screws on the bushing. I took a pair of pliers to it though and twisted it back into position. No problems now! It stuck once for a brief moment, but not once more after that (I played about four games or so immediately afterwards). On a side note, I looked at the gap, and it looks like a credit card would be able to fit between the flipper base and the top of the bushing. If the sticking occurs again though and it's not the plastic piece that caused the problem this time, I'll double check the gap issue.

Mission accomplished. Thanks for the help everyone!

Well, get this.. it works for about a week, then starts sticking again. Go figure.

This time I got an allen wrench and adjusted the gap. I don't think that was causing the problem because there was the same amount of give on the right flipper as there was the left flipper, and now I've added a little more just to be safe, and it's still sticking.

Seems to be mechanical though. When it sticks and I turn the power off, it stays stuck. Another thing to note, is when it gets stuck during gameplay and I flip with the other flipper, the stuck flipper always falls back down. Likewise if a ball auto-fires from the plunger lane, the flipper will fall.

Would it be worth replacing the coil sleeve? Any other ideas?

I have, that was actually one of the first things I did.

I think my next course of action is playing around with the arm per DCFAN's recommendation, and picking up a new coil stop if that doesn't work. I did notice that the circular piece at the end of the coil stop moves in and out a few millimeters, where as the same piece of the stop on the left flipper is stuck in place solid. I am guessing this piece isn't supposed to be moving at all.

I need to see what else I need at the moment from PinballLife. Will probably order a replacement part or two this weekend for this flipper issue along with whatever else I pick up.

All right, a bit of an update! Thanks to the holidays I had to keep my pinball spending low, so I didn't get around to purchasing replacement flipper parts until last week. After receiving them, with the help of a friend we pulled the coil off. It turns out the underlying issue was that the plunger link/rod was mushrooming at the end and eating into the coil sleeve, causing the flipper to stick. Also, the small circular nub on the coil stop had come loose and you could jiggle it back and forth. The end of the plunger was filed down, the coil sleeve and coil stop were both replaced, and all is perfect once again!

Thank you to everyone that has contributed advice to this thread. This is my first major flipper problem since I've owned machines this last year, so it's been a great learning experience. Many of the suggestions weren't the cause of the problem, however, they are all completely appreciated, possibly even more so than what the actual problem was. With all this advice, I should now have no problem troubleshooting flipper issues on my own games in the future, no thanks to just about every possible angle thrown at me in this thread.

You could try adjusting your EOS switch.

Manually force the leaf switch arms with your hands or with a tool. Long needle nose pliers, or a leaf switch adjuster tool. Push them up or something and see what happens. The metal "leafs" will bend upwards or downwards if you give them pressure and bend them. They should be fine as long as both leafs are making the normally closed contact, so I wouldn't worry about damaging them (worst case if you do, buy new ones). The goal is to adjust the leafs to where the actuator doesn't get stuck on them.

Great! I'm glad that worked for you. Simple solutions that actually work are always the best!