EM (Electromechanical) Pinball Troubleshooting


New: Rebuild Williams and Bally Scoring Motors


A. Caution
B. General Info
    1) Getting Started
    2) What Is EM?
    3) Score Motor
    4) What Not To Do
C. Score Reels
    1) Gottlieb
    2) Williams
D.  Scoring Motors
    1) Williams and Bally Score Motor
    2) Gottlieb Score Motor
E.  Stepper Units
    1) Cleaning and Adjusting Stepper Units

Pinball machines contain potentially lethal voltage.  Dangerous voltage may remain for a period even after it is unplugged.  Prior to opening a pinball machine, be certain to unplug it, then turn it on to insure that it was actually unplugged.  It is recommended that the machine be allowed to sit several minutes to allow any remaining power to dissipate. Voltages as high as 120 VAC can be present on any plugged in machine and it can be lethal.

Repair should be left to properly trained personnel.  If you are not qualified, you should not work on a pinball machine.

Solvents such as isopropyl alcohol  should be used only in a well ventilated area. Do not operate the pinball machine until the vapor has dissipated. A spark in a machine can cause a fire. Follow all the warnings on the container. Never use WD40 on a pinball machine.

Proceed at your own risk!

Getting Started

It is with some trepidation that I write this section. Prior to proceeding, ask your self the following questions:

1) Am I good with mechanical items. Can I take apart [?], figure out what is wrong and put it back together, and more often than not, it works.

2) Am I patient? Organized?

If the answer to either of these two is not a resounding “YES”, then find someone else to work on your pin. They may look like something one can tackle, but they are amazingly complicated wonders.

What is EM?

What is a EM pin? EM stands for “electrical mechanical” meaning relays, spinning reels, etc. Newer pins are SS (solid state), a perhaps outdated phrase for electronics, transistors, IC chips, and computers. And we frequently use the shortened “pin” to stand for pinball machine.

Backglass of a EM
Abra Ca Dabra – A Gottlieb EM

EM pins do not have circuit board and many consider them easier to work on as they do not require complex electronic troubleshooting skills. Yet EM pins evolved to be quite complex engineering marvels with complex circuit diagrams and any small little problem can cause them to stop working. A spinning motor may not be the problem, but something else, not obviously related, can be the issue.

How do you know if you have an EM pin? If your pinball machine has spinning scoring reels, like that on the right, it is EM. If the displays are electronic, glow and disappear when it is turned off, it is SS and this section is not appropriate for you.

Note: For most photos click for a larger image.

That Thing Under the Playfield Keeps Spinning!

Gottlieb Score Motor
Gottlieb Score Motor
To access these switches, there are cotter pins
holding the entire unit in position. Remove
those and the assembly can be repositioned
for easier access.

To the left is the score motor from a Gottlieb pin. In many ways, it is the heart of the EM pin. The single biggest complaint is that this motor just keeps on spinning and never stops. As a result, most people start trying to troubleshoot the scoring motor. However, many times, the spinning scoring motor is a symptom of something else that is wrong. Scoring motors in Williams, Bally, Chicago Coin and others look different, but they all serve the same function.

While called a scoring motor, its is also used to reset the machine on start up. That would involve clearing the number of players, resetting the score (scoring reels) and the ball in play. If those other resets do not happen, then the scoring motor will continue to spin endlessly.

The scoring motor spins at start up to reset the pin. Everything, except # games, get reset to zero. That means the scoring reels (display player’s score) must reset to zero – all of them. Ball in play – zero. For multiplayer games, player number must be reset. If any of those are not zero, fix that first.

Williams Score Motor
Williams Score Motor
To access the switches, remove the Phillips
screws to the left and right of the switches.
Even though the wires are still attached, the
entire line of leaf switches will now swing
out for easier access to adjust and clean.

“But everything reset, and my scoring motor keeps spinning! What do I do now?” Just because a reel resets to zero, doesn’t mean that the scoring reel knows it. There is a switch on each reel, ball in play, etc. that must make contact. If they do not, then the scoring reel just keeps spinning. The switch must touch and make electrical contact. It may be necessary to bend it or clean it – but don’t do that yet! Also, a stuck switch on the coin mechanism can cause the reel to keep spinning. Or a stuck tilt sensor. Plus the reel has a ‘home’ switch that gets used with each spin and must work for it to stop.

Gottlieb Ball In Play Reel
A Gottlieb Ball In Play Reel – Located in Backbox One solenoid advances the ball in play, another one resets it. This was all gummed up, preventing reset. Cleaning it fixed the spinning scoring motor below the playfield.

A malfunctioning score motor can cause all sorts of issues. A switch that does not close when it is supposed to can prevent scoring, not count the ball in play as being over, or not reset the active player. A switch that stays closed can lead to anomalies such as scores 5x that they are supposed to be.

In most cases, any scoring that does not start with a “1” involves the scoring motor. For example, scoring a “50” or “500” requires the scoring motor to spin and strike a switch 5 times.

We will get into troubleshooting later.

What Not To Do – And Do

If you have progressed to the point where you are ready to work on the contacts, remember the following cautions:

Reel Disassembled
Ball In Play Reel Disassembled for Cleaning. How the heck am I going to get that back together?

1) Never use anything flammable in any significant quantity. There are all sorts of examples of people setting their machine on fire using WD40 or other contact cleaners. Just do not do it.  And don’t use WD40 any time at any amount.

2) Don’t work on a live game or anything plugged in. Even if it is turned off, a plugged in game can still be a lethal shock hazard. See ‘cautions’ at the beginning of this article.

3) Get the right tools! It is much easier to adjust switches using a flexstone and switch adjusting tools from pinball parts suppliers, than sandpaper / files and needle nose pliers. More switches get ruined by aggressive bending than any other cause. Learn how to adjust switches correctly.

4) Lubrication. Get the stuff that works best on EM machines and is not flammable. Pinball parts suppliers sell the right stuff. Use lubrication on on parts that require it. That is usually just motors and metal to metal contacts. Most parts are meant to be run dry and lubrication just gums up the works.

5) Springs wear out. If a part does not reset or pull in, resist the temptation to stretch out that spring to increase the tension. In most cases, the spring is fine, but the part is gummed up and needs to be cleaned. In other cases, the spring is weak and should be replaced. A stretched out spring may, in some cases help, but it is usually a short term fix and will cause problems in the future. If stretching the spring a bit fixes the problem, order a new one and replace the worn out spring.

6) Take pictures. Lots of them. Digital cameras are your best friend. When taking apart a reel to clean it, all sorts of parts just begin to fall out. Remove that retaining ring and it may be all over. Sometimes, having another person to take photos is necessary. That plastic gear may need to be put back on, aimed in one direction, for it to work. Getting it all back in, in the right order, at the right position can be a challenge. On a disassembled item, your photos may be your only guide.

Part two: Cleaning up those Score Reels!

Part three: Rebuilding the Score Motor.

Part four: Cleaning and Adjusting Stepper Units.


Comments, including suggestions, improvements, errors, etc. are welcome (see below).

If you have a specific question about your game that does not directly apply to this page, please see our FAQ section.

Special Thanks To:

Nic Schell
Roanoke Pinball Museum 

Additional Resources:
Clay’s guide

Copyright 2014 – 2020, all rights reserved.

3 thoughts on “EM (Electromechanical) Pinball Troubleshooting”

  1. WOW! Did I stumble on a superb pinball site. No fluff, only quality information. My game is Gottlieb’s Crosstown, which I have kept running with TLC . It’s a blast to play and my grandkids love it! So glad you have provided sound information on LEDs. Thanks for your site.

    1. Thank you for your kind words.
      If you find any areas that we can improve the site, or any mistakes, please let us know. We work on this website for fun and to keep the hobby alive. Our only income is from a few ads that maybe cover the cost of hosting the website.
      You have a great pinball machine. Do the subway doors in the back still work? It is wonderful that you are able to keep it running, so that younger generations can enjoy it and learn about pinball.
      Thanks again.
      -The Home Pinball Repair Team

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