We've got a TOM that randomly and often decides it has a trunk error, when no such error exists. It happens randomly during play (not specifically when the trunk is hit during a turn, a la the 600+ post thread about Ingo's relay fix). But more importantly, it happens during the trunk test as well.

The symptoms are: The trunk test does everything it's supposed to. Trunk optos open/close in the correct sequence, and the DMD icon for the trunk matches the physical trunk face. However, every so often the icon will be replaced by "error", even though the optos are showing the correct status & the physical trunk is doing the right thing.

Most times, hitting the same + or - button again causes the error to clear and the icon to appear again. Sometimes, this is accompanied by the trunk moving a tiny bit (though the opto status continues to be correct, as it previously already was), but sometimes there's no additional "jog", just a cleared error. Once in a while, the trunk will just skip to the next face, instead of fixing the current face.

We've checked the set screw alignment on the opto wheel (which is the aluminum upgrade version). We've cleaned/rebuilt the gear box and lubed with teflon lube. There is a small amount of slop in the mechanism - you can turn the trunk with your hand and it'll "snap" into a new position a couple of degrees from where it was without moving the motor. As far as I can tell, that might be due to some wear on one of the secondary gears. As the opto wheel slits are very narrow, a couple of degrees is enough to change the opto status.

I found this post that indicates that a "mixed signal" or time-out will throw a trunk error, even if the physical trunk is behaving correctly. My gut tells me maybe the slop in the mechanism is causing such a situation - but the rest of me feels like someone upstream should have expected some slop, and that maybe there's a way to get it running properly without buying a whole new gear box.

During play, the problem manifests as normal operation for a while, and then the trunk suddenly ceasing to move and the game rules acting as if it's been disabled. As mentioned, it's not necessarily concurrent with a ball hitting the trunk. Subsequent self-test says "trunk error - use trunk test". The error can be cleared with the test, since the test does not show errors as described above 100% of the time. Wash, rinse, repeat.

Has anyone else observed / solved this issue?

An update, for anyone who's interested: On a hunch, I moved the opto interrupter wheel down on its shaft and taped some card stock around the edge, so that I could try out different sizes for the interrupter slot. By making the slot 2-3x larger, it seems that the symptoms in Trunk Test mode were improved - the mysterious error messages went away.

However, when in play mode, the trunk still fails. I say "play mode", because I tested by manually moving a ball past the eddy sensor, rather than bashing it into the trunk, to rule out issues stemming from physical impact. The trunk will spin correctly once or twice, but then fail, leading to "trunk error - use trunk test" in the diagnostic messages. As mentioned, it fails while spinning, with no simultaneous ball hits.

At this point I'm wondering if smoothing out or buffering the signal from the opto board in some way might help? It seems likely the software is getting signals it doesn't like, but which aren't evident to the human eye.

Further update: reflowed the components on the opto & motor boards, per the suggestions on Kimball's Pinballs site. No change.

Even tried building a "skirt" around the opto board, on the off chance that stray IR from all the LED's we've installed was causing optical interference. (You can trigger an opto by shining a sufficiently bright LED flashlight into it. Neat trick for testing the receivers.) No change.

Gah!

german-pinball - yes, I believe the opto board is the original one. I'm actually the guy who PM'ed you about buying a board. Just sent another PM a minute ago.

Pin_-_K - thanks for the info. We discovered that the set screws you mentioned were in fact loose. The trunk mechanism now has almost no slop at all. (Unfortunately, it still exhibits the same weird error behavior. So now I'm leaning toward the opto board as a potential source of the problem.)