Your issue lies in the player unit. The player unit advances which player is up as well as what ball you're on. Game off, move the player unit stepper by hand by using the advance coil plunger and make sure the stepper moves 1 spot each time the plunger is moved. It could be that the teeth on the stepper unit have worn and it's not advancing properly. On a 1 player game, when the ball drains, the player stepper advances 4 times to go back to player 1. If it's slipping or not grabbing each gear, it may end up on another player instead. When playing a 4 player game the stepper only moves 1 spot, so less likely to slip.

You said you cleaned the steppers, but look at the ratchet arms and pivot points to make sure they move freely. The grease they used 40 years ago will gum up and cause the arms to stick and the springs can't pull them back where they should be. Make sure everything on that player stepper connected to a spring can move freely.

If after that it's still having issues, then I'd check the score motor switch that pulses the player unit to make sure the switch is gapped and cleaned properly.

Hi Willillist
here https://pinside.com/pinball/forum/topic/gtlb-spirit-of-76-startup-problem#post-3402911 (do not read the text) - look at the second JPG / picture - the Player-Unit is in "Home-Position means player-1 can play ball-1". In post-16 You see "color black - the fifth cam", see the tooth on the cam lifting the switchblades. In that picture towards left we see white-cam-4 and white-cam-3.
Here http://webpages.charter.net/chibler/Pinball/Images/CamPositions-4Player.jpg we see all the cams.

SteveFury made a great topic about reading schematics - here https://pinside.com/pinball/forum/topic/em-pinball-circuits-basics-to-not-so-basic/page/2#post-3162018 and more posts: The Stepping through the players / balls.
A lot of interesting stuff - I point out "post-74". In post-97 I mentioned the "chibler/pinball"-page, in post-94 I point to: http://www.planetimming.com/Pinball/troubleshooting/Player%20Unit%20Troubleshooting.pdf

My "wild theory" To Your problems in stepping through players / balls: the "teeth" on the white-cam-1, -2, -3, -4 are faulty -- maybe in position "third ball" some teeth have broken-off ? Greetings Rolf

Hi Willillist
a corrigenda to my post-7: The schematics shows: Involved in the stepping threough players / balls are cam-2, -3, -4 (not the cam-1), greetings Rolf

There is no switch in an EM that should be permanently closed. Otherwise why make it a switch?

Hi Willillist
Look at the bottom of the JPG - "Coin-Unit set for a 4-Player-Game" and "Coin-Unit set for a 3-Player-Game" --- a bit above "with no text": "Coin-Unit set for a 1-Player-Game".
Once the game is ready for a game: These Switches stay permanent for the rest of the game.

The stepping (example: 3-Player-Game, end of player-3-ball-1) is tricky - not so easy to understand. Involved are the P2-G / P3-G / P4-G switches --- they close and open as the Player-Unit is stepped - and the stepping from "3-Player-game, end of player-3-ball-1" to "player-1-ball-2" needs TWO steps.
We can say 100% sure and easy: In a 4-Player-game: ALWAYS ONE step (next Player gets a ball).
We can say 100% sure and easy: In a 1-Player-game: ALWAYS FOUR steps as the unit must hop over "2nd player" and hop over "3rd player" and hop over "4th player" and hops to "next ball for player-1". And the other types are tricky.

Do You see (?) When we play a 3-Player-game: The "AA" and (only) the "DD" are involved.
Please concentrate Your testing to a THREE-Player-game and write about the VERY first fault showing-up. Greetings Rolf

0Spirit76-Work-09 (resized).jpg

On a one-payer game, watch the player unit after Ball 1 drains. As Mike said, it should pulse 4 times. Each pulse should move the player unit one notch (rivet). Does it attempt to do this?

Also, clean the rivets on your player unit with Scotchbrite pad or sandpaper.

Did you look at the metal ratchet gear and arms on the other side with all the springs attached? The arms need to move freely and the springs pull the arms back immediately.

I know lately, on the player unit, the 40 year old grease has set up and become sticky. I've had to disassemble, remove the old lubricant, clean the pivot points, relubricate and reassemble. If the ratchet arms don't return when the plunger advances the unit, the disc won't advance. Be careful as there are nuts on the back side that need to be removed first as the shoulder bolts are also threaded thru the player bracket and not removing the nut first will break the bolts.

Is it a good idea for troubleshooting EMs with this type of issue, to disconnect scoring mechs for 2-4?

It's this type of wackiness that does scare me a bit on buying a EM eventually as I am not an electrician.

Hi Willillist
the topic is no longer "marked as HOT topic" - I am allowed (again) to write a post. It is nice You could ONCE play a 3-player-game.
Please start a new 3-player-game and when You launch the first ball on Player-1: YOU MANUALLY make some "ten points" --- so the U-first-Ball-Relay pulls-in and stays pulling (we NEED this). Then play through the players / balls - write about the first fault showing-up. (Always do manually make some ten points on Player-1-Ball-1.)

IF (if, if) You can play a 3-player-game - like maybe five such games and the pin ALWAYS behaves as should: THEN start a 2-Player-game - do not forget to manually make some ten points on Player-1-Ball-1 --- what is the very first fault showing-up in a TWO-Player-game ? Greetings Rolf

No schematic handy, but I have bought and repaired a SO76 a long time ago. dim down the lights on end of ball and look for a sparking leaf switch on the score motor. It sounds to me like the player unit is only being hit with one pulse when it should be getting 4 or fewer (depending on the number of players).

Hi Willillist
Yes, the Score-Motor-Switch-1A is mechanically actuated five times - but current flowing through the mechanically closed switch: In a 4-player-game: ONCE --- In a 3-player-game: ONCE or TWICE (when stepping from player-3-ball-1 to (hop-over player-1-ball-1) to player-1-ball-2).

While waiting for the result of a testing a 3-player-game I made the JPG. Here https://pinside.com/pinball/forum/topic/em-pinball-circuits-basics-to-not-so-basic/page/2#post-3162088 scroll down to the visualization "3 player 5 ball" - watch for a minute the animation - see the "hop hop" at "end of player-3 (hop hop to) player-1 (next ball)". In my JPG this is "end of player-3 = Gamma" - "hop to Delta" and "hop to Epsylon = next ball for player-1. Greetings Rolf

0Spirit76-Work-11 (resized).jpg

Hi Willillist
the video is good - especially the slow-motion, the information rather sparse - what was the starting-position ? and what is the end-position ? (I guess: Player-1-Ball-3 --- Player-4-Ball-3 (?))

Do You have the manual and the list of Score-Motor-Switches ? I show "Super Soccer". In the JPG I also show some pictures copied from http://www.pinwiki.com/wiki/index.php?title=EM_Repair#Gottlieb.C2.AE_Score_Motor .

The Switch SCM-1A in question has soldered-on: Wire-black-white-red, wire-white-slade.
Maybe (maybe) this switch is not always closed (when it should) ?. Toggle-off the pin and look at the switch - may want to try to bend the "stationary (not moved) blade" just a bit towards the "moved blade" --- so the switch securely closes ? Of course - when the switch is not actuated: Switch MUST be open.

Please write "what was the starting-position ? and what is the end-position ? in the video".
Please write about an 3-player-game. Greetings Rolf

0Super-Soccer-Score-Motor-some-sws (resized).jpg