Sounds like I may have a similar problem but not sure. Very strange things are afoot.

Something more seems to be happening more and more now on top of it unwantingly choosing a mission on a flipper press at random times, either at start of game or in mid-game.

It will suddenly add a ball as if it thinks the ball has drained. As well, sometimes it doesn't seem to register that the ball has drained and goes searching for it.

I noticed once while I was in a Vengeance Multiball mission that after all the balls drained, the mission didn't end and when I hit the flipper buttons, it kept adding to the score. Only if I held off for awhile would it go into ball search and it did that a few times before it finally ended the mission.

So, a bunch of wonky stuff going on, but I don't know enough to figure out where to begin looking for trouble. I'm hoping what I've described can help narrow down the possibilities somewhat.

It started off as the mission selecting thing a couple months ago and was slightly annoying, but now it has gotten exponentially worse and close to unplayable until fixed. If I can't figure it out, may need to get somebody over to help out.

I posted to a couple of other threads, but forgot this one. I solved my problem. It was pretty blatant when I really got under the hood. I had suspected that the problem had something to do with the trough and turned out I was right, but not in the way I had imagined. I thought that maybe the optos were going bad, or dirty, or just needed to be fiddled with. I had peered around it before but didn't see anything out of sorts, so today I pulled off the metal top cover and something immediately caught my eye. A big fat black post rubber had lodged itself right in the middle of the trough. It must have been there for a good long time too, because I had replaced most of the rubbers with Superbands quite awhile ago. One must have rolled down there without me knowing it, and because it was black, it was next to impossible to see without pulling the cover off. That so explains why I would sometimes get the annoying mission selection problem and it just kept getting worse over time as it got wedged further and further along. Lol, omg I feel like such a chump! Seems like such an obvious thing now, but I guess this is all part of my education in how these things work.

My problem isn't fixed like I thought. Too good to be true. The other things weren't helping, but there is something deeper going on that I just can't fathom.

I can't figure out why the flipper buttons will make the score increase by exactly 1250 points. Not every button press, but randomly. It doesn't always happen right away when I turn on the machine for the first time either. Sometimes it takes a game or two to start happening, but not always.

Basically I can just start a mission and the ball will be in play. I can remove the ball and just keep hitting the flippers and the score will continue to increase by the before mentioned amount. There's nothing else happening on the board.

I've gone through and looked at all the alignments of the optos and switches and everything looks ok to my eyes. Everything plays works as it should during normal play. No problems with the Vengeance drop target at all. It even used to stick sometimes, but that has even seemed to gone away.

Could it be some wiring gone wrong here? Something bad on the main board? I'm not qualified to figure something like that out. I thought I had it all put to bed with that trough deal, but now I'm back to square one.

Ugh.

Took your advice and tried cleaning all the optos I could with some rubbing alcohol and fiddled with opto boards, eyeballing the alignments. They all looked good to me. Switch tests all looked good and tapping around the playfield did not trigger anything, nor did it advance the score like the flipper buttons.

After cleaning I played a few games and so far it is not happening any more so I am keeping my fingers crossed, but I have been down this road before when I thought I had it fixed before. Time will tell. I REALLY hope it was just some dirty optos in need of some TLC. I don't even know if I was reaching some of them that well. I'll have to go pick up some proper Q-tips as I didn't have any on hand. I used a make shift one with a little stick and some cotton gauze I fashioned into one. Hard to tell if I was really getting it far enough in some of those small holes though.

If this is truly the problem, and we are indeed having the same problem, I'm still scratching my head how it is happening. I don't get the relationship between the flipper button and the optos, and specifically that one for you, and perhaps me as well upon closer inspection.

If it is due to vibration alone from the flipper action, then I should easily be able to reproduce it simply by nudging the ramp with the flaky opto. If the opto is in a constant state of being triggered, then why only score increases when the flipper buttons are pressed? Wouldn't it just happen by itself without touching anything? Just trying to think what physically is happening when you press the flipper button. I'm ruling out vibration, so it has to be electrical in some way. I have no idea how the flipper buttons are wired, but they integrate into the code more than just causing the flipper coils to activate, since they also cause the info screen and missions to cycle. There may be something more to that side of things as some kind of short or funkiness in that wiring setup could be causing the problem as well. I'm just speculating in the extreme though.

I'm not sure if I know if I'm troubleshooting the optos correctly though. I assume that if I can get them to trigger that they are working correctly. Is there something beyond that? When I have more time I'll really have to get in there take some closer looks around.

I played several games before work today and wasn't having any problems so I'm hopeful that the cleaning did the trick this time. I'll just have to keep playing and see. I just wish I had more time to play than I do right now. :p

Another day of playing a bit before work with no problems so getting pretty confident that cleaning the optos, such as I did, fixed the problem. This is the longest I've gone without it creeping back so I'm pretty damn happy right now. It's a nice feeling to be able to select a mission without it starting one you may not want to and other weird things happening.