Many thanks, vid1900 et al. Was experiencing resets on my Alien Poker when firing both flippers simultaneously. Took a little chasing but found the problem and now have a more reliable power supply and eliminated a fire hazard I didn't even know existed.

After re-seating all power connections with no luck, started researching and found this thread. Replaced three Suspect MPU molex connectors, both bridge rectifiers (including fuse install), both big beefy diodes, the 12v capacitor and the 5v regulator. Still no go. Found a rusted/corroded fuse holder on the 12v circuit and replaced it.

Still no go. Only thing left was flipper coil diodes. Clipped one end on each and all tested ok. Went ahead and replaced them since I had to solder on them anyway. Low and behold, new diodes solved it! Can't say if it was a bad diode or a bad joint as the culprit but who cares at this point?

Separate issue - any idea if the double flippers on the right are supposed to be able to flip separately? Mine fire together. Can't press the button half way and get one to fire alone. Is this normal?

Seems I spoke too soon. Problem returned. Did a little more research while out of town last week.

For those who don't know, the flipper circuit is pretty simple on System 6 games (couldn't find a diagram online): from the bridge rectifier through the power supply to the flipper coil then on to the flipper button switch and back to the MPU to ground. The MPU simply throws a relay when the game is started, allowing the flipper button switch, when pressed, to complete the circuit to ground (sending current through the coil).

This got me thinking that my issue was likely related to completing the circuit to ground on three flipper solenoids simultaneously... seems the only way this could affect the MPU since there was no transistor or anything firing the flipper.

Anyway, since I was out of town and wanted to get this fixed with only a single parts order, decided to replace coils to rule that out (several of the solder tabs were simply eroded away and guessed my solder job may have compromised something). Figured what the hell I'll do rebuilds on all of them while I'm at it so ordered the complete assemblies from Pinballlife (Terry was happy to replace the EOS switch with vid's suggestion 03-7811 on each). Opted for the original replacements vs the newer version since I didn't have the playfield around to verify clearances.

Soldered those suckers in this morning. No beuno. Replaced the 9-pin molex where the flipper circuits return to ground (2J12). Nada.

About out of ideas now so removed all connectors and pulled the MPU (Rottendog 327) to look at the back side. All good there. Hmm. For kicks, installed a jumper wire under one of the mounting screws when I reinstalled it and connected the other end to the ground braid.

Voila. That was it. Poor grounding on the MPU was resetting the game when all three flipper coils were energized simultaneously.

So, after all the hair pulling and parts-replacing, it was $0.10 worth of wire and crimp-on ring connectors that fixed me up.

At least I've got a bulletproof power supply, fused bridge rectifiers and snappy new flippers now. Should be good for a while.

For what it's worth, I replaced the right-side flipper switch as well. One of the contacts had gone south and a previous owner tied both flipper circuits to the same contact. I've got staged flippers now too.

See my post #552 just above. The flipper circuit is pretty simple. Really no MPU interaction other than the relay at the start of a game. If the solders look good on both coils, I'd suspect one of the connections. You've got one on the power supply board, one between the bottome of the playfield and the cabinet (from the coil to the flipper button) and then one on the MPU where the relay ties in. The flipper button leaf switch sends the circuit to ground via the relay so you should have power at the coil at all times. You can check that and off the top of my head, you should have power on one side of the flipper button leaf switch at all times. Should help to determine where the connection is bad. I'm going memory here so someone else chime in if I'm leading him down the wrong path.