Your score motor home position switch (called the "runout" switch) is opening too early or is permanently open and is stopping the cycle before it can be triggered again perhaps

Ooh boy, I'm not sure - I think it might vary too. Check on the inside of your cabinet, before this time it was usually stapled inside of the cabinet along with the rest of the score motor switch positions, but unfortunately around the time Duotron came out they started to not use these and they put them on a special area of the schematic instead.

If I had my Magnotron schematic with me I'd let you know myself (they're probably the same) but unfortunately it's not here.

Perhaps somebody with another multiplayer schematic of the period will show up.

Check Motor 1C, I forget I had a few Gottlieb schematics I downloaded for the hell of it online

They put them in the manual, not on the schematic.

The schematic will have the various levels of the score motor, how many switches on each level, and the normal state of the switches in each stack at each level. The schematic also had the motor sequence on it, but what each individual switch in each individual stack did was in the manual.

I would think the ultimate EM guide creator would be aware of this.

In any case, 1C inside switch would be the runout switch you're looking for. I don't think that's the issue, but it won't hurt to look at it.

You didn't mention what the score reels etc are doing during the motor cycle.

The add coil on the player unit should start firing and move the startup along. The circuit should run thru the P3 and P4 switchstacks on player unit, motor switch 1A, reset control relay on bank and a switch on P5.

Looking at schematics for Jumping Jack which I believe would be similar to Duotron. Check the ZB contacts...if they are bunched up that would cause the PB relay to trip immediately and prevent SB2 from operating.

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If the score motor is turning 1/3 turn upon hitting the credit button, the score motor run-out switch is OK. It is N/O at the end of each rev.

Per the schematic shown, SB2 is probably operating properly as well, meaning nothing is wrong with the ZB relay. Since the game is silent when SB2 trips, (at the end of the 1st score motor rev), it may be the secondary or multi-player reset completed relay, which will keep the score motor running, allowing more time for the score reels to reach "0." You can manually reset the SB2 relay to see if the reset continues on once the game stops. I can't tell by relay abbrevs, I need to know the full name of the relay to be accurate.

I would also try removing the entire bank assembly from it's housing bracket and rest it on top, (without tightening the wing nuts), and try restarting again. Make sure 1st ball, last ball, game-over/tilt relays are tripped before simulating. Many times, housing the unit limits the bank reset bar of it's full travel and may not make or break all the switches properly, yet, everything may look good upon visual inspection because you lifted the unit out of its bracket. Lifting the bank out of the bracket will allow more room for the bar and may give you different results.

Brian,

the 1st-ball relay normally gets energized by the 10 or 100 point relay, (in the backbox). There is a N/O switch on each of these relays that closes when these points are scored.

The 1st-ball relay itself has a N/C switch, (when NOT tripped), that completes the circuit to its own coil, (so when the relay trips, can turn the coil off). If this switch doesn't have contact, the relay will never energize. This is the most common problem.