On my Embryon today, my pop bumpers have started to randomly fire. All four of them will pop, with no pattern or anything. I've seen a lot of posts about flipper coils causing this problem due to EMI, but when I put the game into test mode, the pop bumpers start firing. I'm pretty sure it is a switch matrix problem because they stop firing when I unplug J2 from the MPU. I tested the diodes of the pop bumper switches (they are good) and clipped the capacitors on the pop bumper switches, and just about all the other switches in the playfield. I checked the MPU and reflowed solder headers, checked the resistors, PIA, etc. Any ideas?

I'll also note that I swapped a new 6821 PIA chip at U10 on the MPU with no change. Also, it is only the pop bumpers that are firing, no other coils. The pop bumper switches are all on the same column in the switch matrix. The sling shot switches are also on the same column, but they do not randomly fire.

The MPU header pins have been replaced, but not the pins on the molex connector. They look ok and I would think other coils, such as the slingshots, would be firing too since they are in the same column in the switch matrix.

Bump, anyone else have this issue?

Yes, I'll put the game in test mode on the switch mode test, pull the balls out of the trough and make sure all drop targets are up so no switches are closed. The pop bumpers will randomly fire. Most of the time, no switch closure registers on the game, although I get an occasional switch closure on #29, which is one of the playfield stand up switches, but everything looks fine, diode tests good and capacitor has been clipped.

All four pop bumpers fire randomly, usually not at the rime, buy sometimes in quick succession, or the same pop bumper will fire a few times in a row. No patterns though. I hope to look at this again this afternoon.

I should note that this issue just started yesterday. I've had the game for over a month with no issues.

No, pop bumpers do not fire in unison with the lamp test. Putting all of the drop targets down also makes no difference.

I don't think it is a SDB issue as the issue stops when I unplug J2 from the MPU, which is the switch matrix. It seems like it is a switch matrix issue. No other coils fire and the TTL chips control more than just the pop bumpers.

Switches are gapped appropriately. I've actually watched to make sure the switch doesn't close when the pop bumper fires.

Life had gotten busy for the last week or so, but I wanted to work on Embryon again and turned it on and now it is working perfectly. I didn't do anything, just haven't turned it on in a week or so. If it starts happening again, I'll post info on what I find, but for now, I'll leave well enough alone.