If you're saying that the some of Player 1's bonus gets added to Player 1 and then some of Player 1's bonus gets added to Player 2, does the Player unit move when the change happens from adding to Player 1 to adding to Player 2?

I'm trying to understand the symptom you're reporting.

That's wild. I also wonder if the player unit is advancing prematurely. You can prop the playfield up and run a game while viewing the internals. I think the player unit may be in the head though.

And in the post right before my question, too!

Does the Player unit step up solenoid fire when the player unit moves?
And if so, is the Ball Index relay activated when the Player unit step up solenoid fires?

Hi WhiskeyTango
I can come up with a theory --- but the thory is a bit "whacky" as with my theory You also should have problems in a ONE-Player-Game --- You should have mentioned in post-1: "Two-Player-Game ..." and in a ONE-Player-Game the new ball is kicked out BEFORE all the bonus is counted down" --- and You did NOT write the mentioned problem on ONE-Player-Games.

The big question (Two-Player-Games) is: Does the fault SOMETIMES show up ? --- or does the fault ALWAYS show up ? ALWAYS the same ? Hard to detect are the "SOMETIMES" faults. Another thing of interest is "Does the faulty counting on the second player ALWAYS give the last (lets say) FOUR thousands points bonus to Player-Two ?" (((And Player-ONE has gotten the bonus BEFORE the four-thousands ?)))

The "point of interest" to my theory is "Switches on the Bonus-Unit (mounted on the underneath-side of the playfield" --- TWO switches are actuated when the Unit is stepped (one bonus left) to ZERO-Bonus --- one of the switches is an two-bladed switch --- and the other one is a three-bladed Make-and-Brake-Switch --- THIS Make-and-Brake-Switch: All good ? Greetings Rolf

Hi WhiskeyTango
I was asking about "sometimes fault happens" or "always fault happens". I also asked about "what happens in a ONE-Player-Game".

I show what happens in a fully functional Space Mission --- You play a ball - You have made some points and some bonus --- You loose the ball. The Score-Motor is not running so "my red 1 Switch" is as shown in the JPG --- "my red 2 Switch" is OTHER - it is moved as You have some bonus made - the ball lost rolls into the Outhole between the flipper-bats and closes "red 3 switch" --- the coil (red 4) on the Bonus-Relay gets current and pulls-in --- its switches do actuate --- among other switches: "red 5" closes - so the relay stays pulling as "red 6" is closed as there are bonus on the Bonus-Counter-Unit.

The pulling Bonus-Relay makes the Score-Motor run and rhythmically 1000 points and again 1000 points etc. are added to the score-drums. Also the turning Score-Motor makes the Bonus-Unit step down - step by step.

Once the Bonus-Unit steps from "One Bonus left" to "Zero Bonus": "red 6" opens so "red 4" quits pulling so "red 2" moves --- NOW through "red 1, 2, 7" the "red 8" gets current --- the Outhole-Relay pulls-in and says: Now is the time to step on the ball / player and kick out a new ball.

You have a problem or more --- and - or : "red 6, red 2, red 7", greetings Rolf

0Sp-Mi-Work-16 (resized).jpg

Hi WhiskeyTango
in this post I only look at the problem "faulty stepping to next player / next ball - when counting down the bonus-ladder".
A fault can happen AAA: Something in the pin faulty makes an Relay to pull. Then as the relay is pulling: Its switches are entitled to actuate --- these actuating switches cause what we then call "fault happens".
A fault can happen BBB: Te Relay is NOT made pulling --- BUT a switch on the relay is maladjusted --- a bit of shaking / vibration and the switch moves just a bit and (maladjusted) actuate --- this causes what we say "fault happens".

To find out if we have AAA or have BBB: A Test-Light mounted parallel to the "Coil on relay in question" is helpful. Looooong wires are at the Test-Light - we clip-on / mount the Test-Light and take it through the open coin-door out into the open --- we play and have an eye on the Test-Light --- and so we "see" what the relay is doing --- beeing faulty actuated (AAA) or not beeing actuated - and from the absence of AAA we then clue "must be BBB".

Here https://pinside.com/pinball/forum/topic/what-is-this-8#post-3791310 ONLY LOOK at the JPG --- the "OK stuff": Two car-lamps of 12 Volts mounted to make an 24 Volt Test-Light --- in the upper right corner of the JPG: "any coil" --- see how the Test-Light is hooked onto "Coil on a relay".

The Relay (COIL) I would like to mount such an Test-Light is the Outhole-Relay (COIL) --- then do some testing --- the big question is: Do You have AAA or BBB ?
When its AAA: In here in post-17, JPG: A fault MUST be in "my red 2, my red 7". Greetings Rolf

Hi WhiskeyTango
in this post I only look at the "stepping down the bonus ladder and at the same time making some thousands of points". Actually there are two (Sub) Features running parallel / at the same time. So the result in a running pin is "as many bonus" - "as many tousands of points added".

The ball is lost and then the pin makes the Bonus-Relay pull-in - it stays pulling until a switch opens when the Bonus-Unit reaches Zero-Position. The constantly pulling Bonus-Relay makes the Score-Motor run. See JPG
Sub-Feature-1, top of JPG: On the Impulse-Cam the switch IMP-C (marked green) pulses, fires shots of electricity to "Bonus-Unit-Reset-Coil (so the Bonus-Unit steps down and down).
Sub-Feature-2, a bit below in the JPG: On the Impulse-Cam the switch IMP-D (marked brown) pulses, fires shots of electricity to the 1000-Point-Relay.

Want to practice "reading schematics" (?) - in the last ball we are rewarded "DOUBLE Bonus" --- the Bonus-Relay is made pulling AND the Double-Bonus-Relay is made pulling --- see that the stepping on both features are done "in another way" (?).

I like my Space Mission --- when I am troubleshooting and for some reasons I NEED a "Turn" of the Score-Motor (((in Williams and Bally pins: Half a revolution, Gottlieb: A third of a revolution))) --- I gently press and let go the topmost switchblade on the INDEX-Wheel sitting next to the real motor. Want to try (?) --- Wear rubber gloves (insulation , Safety Reasons) --- have a game started - pin is ready to play a ball - now press down (in the pin) the mentioned switchblade and let go --- see the motor makes a turn. Greetings Rolf

0Sp-Mi-Work-17 (resized).jpg