I recently began work on repairing a 1971 Gottlieb 4 Square. I've done a lot of the basic repairs needed, including flipper rebuilds, replacement of all of the rubbers, and most recently replaced the flipper and alternating relay coils.

My machine has developed a new problem, where when the ones counter needs to cycle over from 9 to 0, the 10s relay gets stuck energized. This causes the score reel to stick, as well as the 0-9 step unit to stay stuck energized as well. I have been able to release the relay by manually turning the back spinner on the 0-9 unit. Once I turn it, operation continues as normal until the ones counter needs to cycle over again.

The switches on the ones score reel appear to match the correct state for 9 while the machine is stuck energized, and then properly reset to the 0 state once I un-stick the step unit. The step unit is able to move freely otherwise for all other steps, and the alternating relay is still working correctly as well. The plunger in the 0-9 step unit is a little loose because the nylon ring that holds it is worn. In order to prevent the plunger from falling out of the coil, I had to adjust the coil down within the step unit. There does not appear to be any mechanical problem in the step unit since it is able to step regularly most of the time.

I do have a full schematic for the machine.

Any ideas what may be causing the relay to stay energized?

Thanks,

I have attached a few sections of the schematic, including the relevant relays, and the runouts. Relay K is the 1000 points, L is 100 point, M is 10 point, and N is 1 point.

I do see that the switch for the on add "tens" units has an extra cross through it. I know the previous owner had done some aftermarket changes (as you can see on the last picture they hotwired the coin return button to reset the game.

I also know that at one point the plunger was missing entirely from the 0-9 step unit, but i don't know if that contributed to any of these issues.

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I also just noticed that sometimes when you score something that should be 1 point, it rings up as 11 points instead. Also when you should score 50, it keeps scoring 52 or 53. I have a sneaking suspicion that these are related.

So I looked a little closer, and it is only 1 scoring as 11 on every other hit. It seems like the lockup is happening when it tries to turn both reels at the same time.

Example from hitting just a bumper that should score 1 with game starting at 0:
0 -> 1 -> 12 -> 13 -> 25 -> 26 -> 37 -> 38 -> 49 -> lockup (because its trying to double-turn the 10s digit from 4 to 6 with a single signal)

It seems like maybe there is a short on the alternating relay?

It was in fact a short on the alternating relay. I found a switch that was stuck closed when it should have been open.

The machine still doesn't trip the alternating relay maybe 1 in 20 hits, but I think that may be just the quirk of an old EM machine....not sure if that will be fixable.

Yeah, A is the alternating relay. The one time i really noticed it not alternating was when I hit the 100 pop bumper when it was already activated. In those cases, the 100 bumper just stays active.

I am still trying to figure out if there is any other pattern.