Rolf, it creates a short pulse that trips the LB (last ball) relay when there is more than one person playing. This short pulse is sandwiched between the 4th and 5th pulse of the motor 1A pulse stream.
They did this in order for the LB trip circuit to use part of the player unit advance and the XB (game over) relay trip circuit. Most of that circuit is designed to do two things:
- Step the player unit advance solenoid the correct amount depending on the number of players selected.
- Trip the XB relay after the last ball has been played by the last player in that game.
If there are two players, for example, then XB must not trip until after the 2nd player has played their last ball.
However, the LB relay must trip at the START of the 1st-player playing the last ball. I will use the example of a 5-ball game and 2 people playing. When the player unit lands at position 16 (1st player, ball 5) there is no current going to the rivets at position 16 because the PB2 switch is open (two people playing). In order to use the player-unit rivets at position 16 to send a pulse to trip the LB relay, a short pulse is sandwiched between the 4th and 5th pulse of the motor 1A pulse stream. This trips the LB relay but does not step the player unit forward or trip the XB relay:
- The player unit advance solenoid does not see the LB trip pulse because the motor 1A switch for the ADD PLAYER UNIT coil is open.
- The XB relay does not see the LB trip pulse because the motor 1C switch is open.
Hope this helps! - TimMe