Fun With Pinball

Gottlieb Score Motor Documentation

(If you want to skip the background material and just generate a Motor Sequence Chart, jump ahead to the Motor Sequence Chart Generator.

Gottlieb Score Motor Switch Stacks

Troubleshooting an electromechanical (EM) pinball machine often requires understanding how the switches mounted to the Score Motor behave. Most Gottlieb schematic diagrams include a Score Motor switch stack table and switch location diagrams like these that specify the number and type of switches at each position around the motor, and where they're located:

Gottlieb Motor Switch Stack Chart example Gottlieb Motor Switch Positions example

In the table the leftmost column represents the position around the circumference of the Score Motor where the switch stacks are mounted. The top row represents the level at which the switch stacks are mounted. The "A" level for example is the lowest level which follows the lower of the two motor cams as shown in the side view of the Score Motor on the right. The "B" level is the next level up, activated by pins mounted between the two motor cams.

The notation in each box in the table represents the number and type of switches mounted in the switch stack at that position. The switch types are:

• A: Normally Open switch
• B: Normally Closed switch
• C: Make/Break switch

So in the table above for example the switch stack at position 2B has "1A, 3B" or one normally open switch and three normally closed switches. There are no switches mounted in positions 1E, 2A, 2D or any other position represented by an empty box in the table.

In addition to the number and types of switches the entries in column "C" include "S" and "L" POS (positions). These indicate how the cam follower is mounted into the switch dog which is the tuning fork looking device shown on the far right. Switch stacks on the "C" level all use the "S" position on the switch dog except for position 2C which uses the "L" position. Only switch stacks on the "C" level use switch dogs, and only the 2C position stack uses the "L" position of the switch dog.

Gottlieb Score Motor Sequence Charts

The switch stack table above is handy but it doesn't include any information about the relative timing of the various switch stacks. If you're lucky your schematic also includes a Score Motor Sequence Chart like this one which corresponds to the switch stack chart above:

Gottlieb Score Motor Sequence Chart example

The black boxes on the Motor Sequence Chart indicate when switch stacks at each position are activated as the Score Motor turns through a complete 120 degree (or ⅓) rotation, which is sometimes called a score motor cycle. So for example switches mounted at position 3B will activate before switches at position 1B and 4C, but after switches mounted at position 2C and 1D.

The video below shows how the Motor Sequence Chart relates to a running Score Motor.

Gottlieb score motor demonstration

This timing information is important to help understand the sequence or order of events in a score motor cycle as switches open and close. This can be key to troubleshooting a circuit that uses Score Motor switches.

Gottlieb used essentially the same Score Motor from the late 1940s through the end of the EM era in the late 1970s. Since the Score Motors are all essentially the same you can recreate the missing Motor Sequence Chart if your schematic only has a switch stack table using the chart generator below.

Score Motor Circuit Animations

To better understand how Score Motor circuits work the Animated Schematics web pages have detailed explanations of common Score Motor circuits like the circuit to score 50 points, and examples of how Score Motor switches can be used in combinations to mask some Score Motor pulses.

Generate a Motor Sequence Chart

If your schematic doesn't have a Motor Sequence Chart like the one above you can use the tool below to generate one. Just click on the check boxes in the table that correspond to the populated boxes in the switch stack chart on your schematic.