What an awesome guide! I found this by coincidence since a friend of mine has a Monte Carlo from 73, which when only playing 1 player, randomly anvances to player 2 after a ball has drained.

Sometimes even when ball 2 drains, it could be advenced to player 3s score field... Hopefully this can shine some light onto why that could happen even thou he only insert 1 coin.

Thanks alot for taking your time and writing this!!

Regards from Sweden

Interesting coincedence, I just fixed the exact same problem in my Space Mission using this guide to understand how it should work (starting at post 44). I'd suggest using a test light and seeing if the ball count step up is firing. From there you can backtrack down the path until you find what's not firing. In my case it was the score motor switch that connects the ball count branch (3B in this game). Every time it failed it wasn't closing - it has worked perfectly ever since adjusting it to close reliably.

I'd love to do this same kind of guide for Space Mission. The circuits aren't exactly the same, and of course some features are different. But this guide made it a whole lot easier to understand some of the mysteries like the game reset and ball drain sequences.

Thanks for the tips! What kind of light test are you referring to?

If you search the forums for "test light" you'll see what I mean - literally just a light bulb (or two) connected to alligator clips. You can use it to quickly check circuit paths to see if they're open or closed. I just bought this one off Amazon for $5 USD and it works perfectly with a bright red LED for both coil and lamp testing (I use a 1 meter set of alligator clips as extension so I can leave it hanging outside the game where I can see it):

https://www.amazon.com/gp/product/B0017RHOKO/ref=ppx_yo_dt_b_asin_title_o00_s01

For example with this issue - start with the light connected across the ball count step up relay. When it's working correctly, you should see it light up after the ball drains; when it's not working (and advances the player instead of the ball count) then you'll see it not light up. Take the clip that is on the switch side of the relay and start moving it down the path that leads to the relay - on the other side of the coin unit, on the other side of the player unit, on the other side of the score motor switch, etc. Once you find the first place that lights up when your problem occurs, then you've found where the switching has failed. You can isolate problems in minutes, very efficient way to trace the game logic.

Of course for maximum effectiveness, you need to understand how the game logic is supposed to work - which gets back to this thread!

Sounds like a great idea . I did actually search for Light Test and got 6032 posts.. but only mentioning the usage of such a tester but not actually showing me what it was :S.

Thanks once again!

Bulb tester
https://pinside.com/pinball/forum/topic/reading-gottlieb-schematics#post-2634425
https://pinside.com/pinball/forum/topic/em-pinball-circuits-basics-to-not-so-basic/page/2#post-3184715

Thank you!

Thanks for the amazon link. I can use this gadget. Great post description on how to use it, too!

Excellent job by @XSVtoys, wish someone would do a Gottlieb 75-77 em the same way,

First I would like to thank you for the great information that you have provided about the Monte Carlo game. I picked up one a month ago for $200. It didn't work when I got it, so I have been following the link here and got it to work. But I still have issues that I can't figure out. 1. Wires to one of the coin door switches was broke. 2. Coil on 0-99 unit was burned up and froze. 3. Bent switch on score motor cam. 4.No power to credit button. And bad rubber on play field.
Now I am down to , 1 no ball in play light. 2. Game over coil won't latch without manual help 3. Ball over switch intermittent. The pic attached is where I am stuck. The blue line on the coin relay won't stay engaged long enough. Thanks

0207201800 (resized).jpg

Thanks for the amazing write up. Hopefully it will help me figure out an issue I'm having. Machine was working perfect. But I decided to replace the pop bumpers and flippers and now only 2 of the 3 pop bumper score doesnt register and 1 of the chime coils locks on. I suspect I bumped a wire somewhere or something.