Wow what a read. PROBLEM IS ALL PSYCHOSOMATIC

I asked a buddy of mine that has a lot of Bally and he said nope never seen the problem.

Well as my luck would have it my Mr and Mrs Pacman does it fairly often. The left top pop seems to be the main one, but funny as i stuck a q tip between the pop switch after cleaning and opening up the gap as friend said " yeah it is just to close" well NO while pf up and i was looking around firing flippers not only did the top pop(which was blocked) but also the left sling shot fired a least once and one of the others (heard sound did not see which one). So as reading thread and well seeing a lot of the trials and testing already done. I guess i could pick up the torch a little and try a few things suggested by you all.

It still seems like no absolute fix which is every ones goal. Some of the fixes like swapping PIA rule that out as i had put two new in and then swapped with two more different ones no change. the ball/tilt suggestion well no ball in there, tilt has braided copper wire soldered to it ( factory) don't know. I have done the separation of the signal wires, lamps, and power from the boards to the PF but that is all. I have not done, the flipper, coin door, AC mains area yet. Doing this has seemed to reduced the occurrence a tad as before i would see it fairly often maybe 10 times or more a game now maybe 4 but just the luck of the timing i don't know.

I have a bunch of nice high V caps all 250V rated wondering what size would be best for the coil EOS switches. 1uF .01uf .1uf or other value? I hooked one up temp and seen reduced blue spark but not GONE each time.
On my schematic it shows caps across the EOS switches with note 5 - .01uf @500v German games only. I can see it being 500V for over there but really what do you think would be the best choice for cap size. Again this is for the EOS at the flipper coil.
DSC00211.JPG

One of the reasons i want to try this as second attempt to help tame my issue is that yes i can tell that it is really random "timing based" flipper noise causing issue and while maybe just my imagination seems to happen at the time of the EOS spark.

Also noted on switch matrix that All on ST-2 line so the random sandwich of lines just makes sense. No switch on this line has a cap across it either, which i noticed effected my directional/movement buttons immensely, they were not there in machine, schematic only referenced one, but putting one cap on each worked a treat. Acted like switch debouncing, now much better movement and directional control.

Anyhow that my story and i'm sticking to it. I only have one Bally and i would be shocked if everyone doesn't have the problem and it is just not noticed.

i ended up putting a 223K or .02uF on the EOS of the left flipper with the New EOS switch. I still see arcing and no change as far as the ghost pops. Played a couple games, i caught it at least once or twice. I did take the cap of of the score switch for that pop and i do not believe any score is given for the randoms.

I have a couple scopes but not a digital storage. Where were you looking at the return line header pin? further in the MPU ?

i am almost wondering if a couple Schmitt triggers or some other pre/post PIA circuit could be added and be done with it.

my machine has original board set. but a mouse on insulation diet does not help i'm sure. just notice the white speaker wire is chewed back about 6'' (he fed mainly in the coin connector area) that is when i noticed the AC main going to the switch woven right in with the flipper power and coin door signals. i thought to my self then hmm.. then found this wonder thread. It is all starting to make perfect MUD.

Yeah i think i will try to separate a bit. I had already done some and seemed ?? *wishful thinking* to help.

I will say I was reading this thread when I first got mmpm

I had many pop fires I did the wire separation as much as I could from mpu ps area and it did seem to quite down.

Later I rebuilt the flippers and while I had it all apart I was going to try the solder tabs away from the coil stop as I hear it is better. Well upon putting back together immediately all kinds of crazyness including game resets. I could not believe it. But as soon as I flipped the coil back and put much shorter EOS wires on. Problem gone. The extra few inches of wire made a huge difference.

Need to re read entire post if you have.issue as lots of things tried.

And lots of people that never had a problem at all.

That is a 2.2 uf cap

Opps bottom pic on different page a few weeks late lol