I actually had about the same problem...with my F-14. Went 'round and 'round with the usual stuff, replacing diodes etc... still had the mysterious random tilts. I finally found that the upper "T" target was causing the tilts. Did the usual diode replacement again on that target. Still tilts.

I took the target switch out and ohm'd it for continuity and proper operation and it appeared to work fine out of the game. Reinstalled it and guess what - still tilted! I ordered a new switch and replaced it, and the problem was gone for good. I never knew what exactly within the switch was causing it, but I suspect that perhaps the rivet through the "sandwich" of the switch base was probably shorting somehow, I just never saw it with a meter.

I assume that your Fire right flipper has a lane change switch off of the cabinet switch. Try replacing the switch along with the diode, unless I am wrong about Fire and your matrix switch triggered by the right flipper is off of the right flipper EOS.

Random tilts are usually switch matrix issues. Typically it's a combination of switches hit together that make the random switch go. It's often due to something being miswired or a diode being installed incorrectly. These are tricky to find! I had this on my CV and it was a miswired switch that took months to find and figure out. Good luck!

Marc

The key is to figure out the pattern, but unfortunately that's not always easy to do. For a false switch indication to occur, three other switches need to be closed at the same time. While that initially sounds unlikely keep in mind any switches that are normally closed or frequently closed (ball trough, ball lock, drop targets etc.). I would go through the video and see if you can spot the pattern of which three switches are closed when the problem occurs. If that doesn't work you can start closing a combination of switches while in test keeping the following in mind.

One of the switches will be in the same row as the playfield tilt and one in the same column as the playfield tilt. The fourth switch when combined with the other two will form a rectangle on the switch matrix. One of those three switches will be the problem.

More info:

http://pinballrehab.com/1-articles/solid-state-repair/repair-guides/146-switch-matrix-theory-and-troubleshooting

This doesn't make sense. How can a bad switch cause this to happen? Unless it was arching inside the stack and going around the diode.

I agree - it was bizarre for sure...and maybe as you said. I did think about tearing the switch apart - for a moment - but figured that in itself might disturb whatever was wrong with the switch construction, and it's around 25 years old. I had fought the problem for so long I was just glad to be done with it.

Just wanted to update this thread.
I have been working on a Fire for a customer, in NY (maybe it's the same game 7 years later?).

System came in with a Rottendog MPU that had blown transistor (the bottom one in the column next to 1J19) then someone accidently put the wrong transistor in to replace it.
We replaced the Rottendog MPU with another in the interest of time.

Once the game was up, I was encountering the same issues - you'd be playing and get a random TILT.
Not necessarily the first game, but usually within 5 games or less.
It had to be the playfield tilt for the same reasons as was stated above (no tilt warnings or sound effects, just instant tilt, and move on to next ball).

- Checked all switches in the game, saw that the playfield switch looked to have been removed at some point and was also separated quite a bit so it definitely wasn't making.

- Put the game on its own dedicated 20A power (have seen issues with random bugs on games that are run on long extension cords and on loaded circuits).

- Assumed we had a random short in a wire affecting the lamp matrix and looked through harnessing but didn't see anything obvious.

- Checked all the diodes on every switch.

- We filmed game play in slow motion and saw the fire lights turn off right after a left flipper actuation (right ramp was in the lower position, center post was raised, left ramp had just raised but it seems that raised JUST after tilt was declared - so timing thing).
We saw the lights of the 'fire' in the playfield dim at that exact time, and the center post lower at that exact time (and it had lowered early, you can tell by the frequency of the flashing light above the post when it should have lowered).

We started investigating that flipper and saw that the left flipper coil had been replaced at some point.
When it was replaced, someone did not install the two diodes needed for this coil. The schematics call for diodes here.

We put the diodes in and played.

We are about 24 games in and have not seen a single random tilt!

The best theory is, lack of diodes on the coil was injecting noise into the system.

Just wanted to update this thread incase someone else experiences random Tilt on a system 11 (or specifically a Fire).

That's really bizzare. The purpose of the diodes, as most know, is to prevent damage to the coil driving circuity from back spikes of voltage created when the coil is shutoff and the magnetic field collapses. This is totally unrelated to the switch matrix and really none of those circuits overlap, unless there was induced noise from the coil circuit playfield wires running close to the switch matrix wires - that's all I can possibly think of, besides some outright coincidence. Wouldn't be the first time something strange happened with a pin.