Check Q5 and associated circuits on the fliptronics board.

Something between the coil and up to and including the fliptronics board. Check transistor, wiring, etc.

Check wire continuity between coil and plug on fliptronics board.

Coolpinballdino did you figure out what the issue was? My TZ started showing the same chattering of the upper left flipper earlier today. I replaced the Rottendog Fliptronics board with the original one, but the issue persisted. Checked the EOS switch, which looked fine. Came to the forum hoping to find some suggestions or insights as to what to try next, then found this thread.

Based on what I've read so far, my (un)educated guess would be either wire connectivity (between coil and fliptronics board), soldering issue (i.e., flaky solder joint at one of the lugs that needs reflowing, I've had that issue with my TZ not too long ago), or failed coil (i.e., where windings connect to the lugs).

Did you try cleaning the opto? Swapping left/right flipper opto boards?

There are a bunch of things it could be, but start with the simplest. Bad/dirty opto can cause this symptom (it did on my machine).

I did not try that (yet), I assumed that if it was the opto board that causes this issue, that both flippers (upper/lower) would be chattering, not just the upper one. But it's straightforward enough to try, thanks for the suggestion!

You're right if it were a problem on the PCB itself, maybe. But there are two opto pairs on each board, one for each flipper, so one flipper can be fine while the other isn't.

Doh, let's call this a 'learning moment' (there's quite a few of those considering the frequency with which my TZ develops issues). I assumed that there was a single circuit to detect whether the flipper button was pressed. Now I know better than to assume without double checking. I swapped the opto boards and the chattering problem stays with the upper left flipper. Thanks for the suggestion / teaching moment though, I do appreciate that a lot!

... to be continued ...

Glad to help. Sorry it didn't turn out to be as simple a problem as that. But at least now you have ruled that out and can work your way back in the circuits and look at the other possibilities.

By the way, you may have not realized, but most of these pins where one button controls two flippers, you can actually control them separately, because they don't get triggered at the same point in the throw of the button.

Typically, a partial press of the button will trigger the lower (main) flipper, and pressing the button all the way will add the upper flipper (the lower one will stay triggered).

I'm not good enough a player myself to take advantage of this, but I've seen other players use it to trap balls on the lower flipper during a multiball, while still operating the upper flipper to hit a remaining ball in play.

On some machines this is implemented using an extra leaf in the switch, but on TZ (and any opto based switch) the interrupting blade that the button moves is notched so that one opto is cleared before the other.

A 'chattering' flipper is NOT the opto on the button PCB. It means that the HOLD coil is not operating. This can be because of a broken coil, broken wire to the coil, or because the hold coil driver (on the fliptronics board) is bad.

A bad EOS wouldn't cause this either, as without the EOS switch being seen, the game 'fakes' the EOS switch.

Learn your TEST MENU, as you can verify the EOS AND flipper button optos in switch test. Hit a flipper button, and you'll see both optos, and each flipper's EOS switch activate. If you don't, that IS something that needs to be addressed, but is NOT the cause for the 'chattering' flipper.

Edit to add: This is NOT TZ specific, but pretty much ALL WPC games.

This was exactly the issue. The coil had gone bad. Someone also had put the wrong kind of coil there, and where the 2 diodes were supposed to be, was a bit of painters tape. Well then. I happened to have the appropriate coil, and after I replaced it, the chatter issues went away and my TZ is now all ready for the next thing to break. Thanks again Coyote!

Wow, you've had several issues with this TZ! I'm glad you're getting it all sorted, though.

... Painter's tape? Really? That's strange, but probably not the strangest thing people've seen on a pinball.