Fun With Pinball

Gottlieb Player Unit Animation

In approximately 1970 Gottlieb introduced a new device into its multi player games called the Player Unit.  Before the Player Unit multiplayer games had a relay for each player to keep track of which player was playing and scoring points. The Player Unit replaced the separate relays with a Step Unit that drives a wiper board over a set of contacts, typical of most steppers, while also driving a number of cams that activate switch stacks, more like a Score Motor

This brief video shows a Player Unit in a four player game going through a complete reset cycle at the start of a new game.

Player Unit resetting at the start of a new game

Note that each time the solenoid plunger in the lower right corner fires the Player Unit advances one step. It pauses twice in the middle of the reset sequence to allow the player 1 & 2 and then player 3 & 4 score reels to reset back to zero.

The Player Unit combines many of the scoring and reset duties into a single device at the cost of some circuit complexity. Understanding the Player Unit is a common stumbling block for those learning to read schematics and troubleshoot games. This page is intended to help demystify one of the Player Unit functions.

Simplified Schematic Diagram for Advancing to the Next Player

Here is a simplified schematic drawing of the Advance Player Unit circuit to illustrate how the Player Unit advances from one player to the next in a four player game as the game is being played. 

Simplified Add Player Unit Schematic DiagramSimplified Add Player Unit Schematic Diagram

In the upper right corner of the schematic is the symbol for a step unit representing the Player Unit.  The small circles represent contacts on the step unit and the double ended arrow shows both the current position of the step unit and which contacts are connected together in that position.  The first five positions of the stepper are all connected to light bulbs to indicate which player and ball is currently playing.  The total number of steps on the Player Unit is not shown and is not necessary for this demonstration.

Below the light bulbs is the Add Player Unit solenoid and the circuit that drives it.  Each time this solenoid fires the Player Unit advances to the next position. Included in this circuit are the Player Unit Pos = [1,2,3] switches which close when the Player Unit is in the specified position.

At the bottom of the schematic are the Score Motor circuit and transformer which provides power to the entire schematic.

In the upper left corner is the Motor Switch Timing Chart which documents when each of the Score Motor switches activates as the motor turns through a complete 120 degree cycle.

Below the motor timing chart are four toggle switches used during the animation.  The Player [1,2,3] toggle switches represent which players are playing the game.  This function is normally handled by the Coin Unit (not shown) but for simplicity toggle switches are used here instead. Each toggle switch controls a switch in the Add Player Unit circuit.

Below the Player toggle switches is another toggle switch that represents the Outhole or Ball Return relay (not shown) which activates when the ball drains into the out hole and the game advances to the next ball.

Because this is a simplified version of the Add Player Unit circuit many other switches have been omitted.  Those switches contribute to resetting the game, inhibiting the ball count from advancing when no points are scored, preventing the Add Player Unit from advancing when the Score Motor turns for other reasons, etc.

Example 1: A one player game

The video below shows what happens during a one player game when the player loses or drains the first ball.  Notice how the Player Unit takes four steps to get from player 1 ball 1 to player 1 ball 2.  This is because it has to skip over the players not playing in this game. If you watch carefully you can see the lights over the scores for players 2, 3 and 4 flash briefly as the Player Unit steps past them.

Player 1 loses the first ball in a one player game

To better understand how this happens the following schematic animation demonstrates what happens to the circuit in this situation. At the start of the simulation the Player 1 Ball 1 light is on and the Outhole relay toggle switch is activated to indicate that the ball has just drained. This starts the Score Motor turning and activates the rest of the circuit. In this situation the Player Unit takes four steps to reach the position which represents Player 1 Ball 2.

First ball drain during a one player game

Notice that the Motor 1A switch next to the Add Player Unit solenoid closes five times (shown in the motor timing chart) as the Score Motor turns through a complete 120 degree cycle.  This switch determines when the Add Player Unit solenoid can fire to advance the Player Unit.  The switches to the right of the Motor 1A switch determine how many times the Motor 1A switch will be allowed to advance the Player Unit.

To the right of the Motor 1A switches are four parallel paths. Any one of them can complete the circuit to the Add Player Unit solenoid as the Motor 1A switch closes. At the bottom of these four paths is a Motor 2C switch which closes once every time the Score Motor turns.  This path is always used whenever the ball drains because the only requirement is that the Score Motor is turning. There are not other switches, or conditions that need to be met, for the path to complete.

The upper three paths to the Add Player Unit each require two switches to be closed for the Add Player Unit solenoid to fire.  One is a switch closed by the cams on the Player Unit (often with labels like P2C, P3E, P4D, etc.) and the other is a switch that is closed unless that player is also playing.  Each pair of switches represents a pair of conditions that needs to be met (in addition to the Score Motor turning) for the path to complete to allow the Player Unit to advance.

So for example for the top path to complete and generate a pulse that will advance the Player Unit the Player Unit must be in position 1 (which would close the first switch) and Player 2 must not have joined in the game at the beginning (which would open the second switch).

In this case to get from Player 1 Ball 1 to Player 1 Ball 2 the Player Unit needs to take four steps.  Each of the four legs in the Add Player Unit circuit will provide one of the four pulses required to fire the Add Player Unit solenoid and advance the Player Unit the four required steps.

Example 2: A two player game

In a two player game the Player Unit takes just a single step when player 1 loses the first ball:

Player 1 loses the first ball in a two player game

The following animation illustrates what happens in this case:

Player 1 first ball drain during a two player game

When Player 1 loses the first ball the Player Unit takes just one step to reach the Player 2 Ball 1 position.  In this case the only pulse to the Add Player Unit solenoid comes through the Motor 2C switch. Even though the Player Unit Pos = 1 switch closes when the Player Unit reaches position 1, a two player game was selected which opens the Player 2 switch so the Player Unit doesn't take any more steps.

When Player 2 loses the first ball in a 2 player game the Player Unit takes three steps to advance to the Player 1 Ball 2 position:

Player 2 loses the first ball in a two player game

Player 2 first ball drain during a two player game

As in the previous case the pulse for the first Player Unit step comes through the Motor 2C switch.  Following that the next two pulses to advance the Player Unit come through the Player 3 and Player 4 switches which are closed during a 2 player game.

Example 3: A three player game

In a three player game the Player Unit takes a single step when the first player loses the first ball:

Player 1 loses the first ball in a three player game

Player 1 first ball drain during a three player game

When Player 1 loses the first ball in a three player game the Player Unit takes just a single step to the Player 2 Ball 1 position.  The pulse for the Add Player Unit solenoid comes through the Motor 2C switch.  The open Player 2 and Player 3 switches prevent any more pulses from reaching the Add Player Unit solenoid.

When Player 2 loses the first ball in a three player game the Player Unit again takes just a single step, this time to the Player 3 Ball 1 position:

Player 2 loses the first ball in a two player game

Player 2 first ball drain during a three player game

When Player 2 drains the first ball in a three player the behavior is essentially the same as when Player 1 drains, with the only pulse to fire the Add Player Unit solenoid coming through the Motor 2C switch. The open Player 2 and Player 3 switches prevent any more pulses from advancing the Player Unit.

When Player 3 drains the first ball in a three player game the Player Unit takes two steps to reach the Player 1 Ball 2 position:

Player 3 loses the first ball in a three player game

Player 3 first ball drain during a three player game

The two pulses to advance the Player Unit from Player 3 Ball 1 to Player 1 Ball 2 come through the Motor 2C switch and through the Player 4 switch.

Animated Schematic Diagrams

Follow these links to other animated schematic diagrams:

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