Ok, you are confident that the lock-in switch on the G relay is clean and adjusted optimally.

The next thing I personally would consider is the possibility that the power to the G-relay circuit is being interrupted momentarily by some other NC switch that is "bouncing" open due to vibration, which would also cause the G relay to drop out.

From the schematic, there are 3 switches on the "power line" (denoted by the vertical line on the far right side), and located at I-10 and I-11, that all must conduct continuously to deliver power to the G relay circuit. They are: the switch on the hold relay, an NC switch on the 6th position of the ball count unit, and an NC switch at zero position on the ball count unit. Additionally, there is the bounce switch located at H-14. If any of those 4 switches were to "bounce open" for a fraction of a second, the G relay will drop out.

Try cleaning and adjusting those switches, just to ensure that power is not being interrupted momentarily.

If that doesn't fix the issue, one other thing you might examine is whether the return spring on the G relay is proper and isn't exerting too much tension to try and return the G relay to rest position.

Other possibilities could be a cracked solder joint on one of those switches or a microbreak in a wire under the insulation, such that vibration is causing momentary loss of power to the circuit. I hope you don't have to go there as those can be tough to find.

One additional question: are your flipper coils standard A-5141 units?

Lee

Is it only the flippers that are resulting in the G-relay dropping out?
Will it drop out if you fire the pop bumpers a few times in close succession?

The reason I asked that question was to try and ascertain whether the issue was vibration induced, or perhaps was resulting from an ultra low-resistance flipper coil that was drawing excessive current away from the other relays in the game.

I might also try exchanging the return spring on the G relay with one from a different relay. Might not help, but it is a quick try. I once had a Gottlieb with a similar dropout issue and it turned out that some prior owner had replaced the return spring with a similar length spring that was much stronger. It took very little vibration for that spring to yank the relay plate back to unenergized position.

Lee