Quoted from rolf_martin_062:
write if You also want to dig-in into closing SCM-1A AND stepping the Player-Unit (One-Player-Game and Two-Player-Game).
I'd like to understand this circuit better than I do and Rolf's drawings got me studying it some more. I think I agree with Rolf and want to elaborate or clarify. There are basically three paths that provide pulses to advance the Player Unit as shown above and that I'll redraw below. Which path is used for any given situation is determined by the Player Unit cam switches and by the PB/Second Player relay switch.
In a one player game the Player Unit gets 4 pulses when the ball drains to step the Player Unit 4 times. In a two player game, when Player 1 drains just 1 pulse is delivered, then when Player 2 drains the remaining 3 pulses are delivered.
Path 1 to the Player Unit is through the Score Motor 2C switch. This path delivers the first pulse any time the ball drains:
Jumping Jack Player Unit 1st path (resized).jpg
Path 2 goes through the PB/2nd Player relay switch:
Jumping Jack Player Unit 3rd path (resized).jpg
And Path 3 bypasses the PB/Second Player relay switch:
Jumping Jack Player Unit 2nd path (resized).jpg
The significant difference between the paths 2 and 3 is the PB/2nd Player relay switch. That switch opens on a 2 player game effectively disabling path 2.
So the generic sequence any time a ball drains is:
- get one Player Unit pulse through the Score Motor 2C switch (path 1)
- if it's a 1 player game get a pulse through the PB relay switch (path 2)
- if the Player Unit has taken two steps (received two pulses) get two more pulses through path 3
On a 1 player game that's pretty straightforward. All three of the steps in the sequence are taken and all three paths are used to get 4 pulses each time the ball drains:
Jumping Jack Player Unit 1P pulses (resized).jpg
Things are much more interesting on a 2 player game. When player 1 drains, one pulse goes through path 1 and advances the Player Unit one step, which closes the P1C switch and (I think) toggles the P2A Make/Break switch to select path 2. Since path 2 is disabled on a 2 player game no more pulses are generated and the Player Unit stays where it is, one step past it's home position. When player 2 drains another pulse goes through path 1 and advances the Player Unit, which leaves the P1C switch closed but again toggles the Make/Break P2A switch effectively selecting path 3. Since path 3 doesn't care about the PB relay switch, the next two pulses advance the Player Unit until the P1C switch opens.
Jumping Jack Player Unit 2P pulses (resized).jpg
If this is all true then I'm a little confused about the P1C and P2A switches. The cam diagrams seem to show that the P1C switch should close one step before the P2A Make/Break switch changes state. But for this scenario to work both would have to change after the 1st Player Unit pulse to use path 2 through the PB/2nd Player relay switch. So perhaps the cams in Jumping Jack are different than the cams in Top Score (which are shown above), or else I'm missing something.