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 Newer pins are SS (solid state), a perhaps outdated phrase for electronics, transistors, IC chips, and computers.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.

19 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

      1. Oh yes, the subway doors open and shut great. I have replaced most of the coils and that has made the game a bit more zippy. Now I am in the process of swapping out the #44/47 bulbs with LEDs. Those incandescents burn hot and actually burned a hole in one of the pop bumpers. One issue I will need some advice on. The four inserts at the top of the play field have sunken to some degree. This tends to trap the ball on occasion. The inserts on the scoring ladder have also sunken to some degree, but do not trap the ball. However, they do affect the ball’s movement somewhat. Any suggestions? Other than that, everything else works as it should! I played this game for countless hours in the early ’60’s. It is a treasure to own it now. Keep up the great work!

        1. It is interesting that you replaced the coils and they now seem a ‘bit more zippy’. Coils do not have any moving parts so they generally never wear out. The wire(s) can break and they will stop working. Or they can overheat and the wires short which could blow a fuse. Or they overheat and melt the core.
          Usually, if the coils seem sluggish, it is that the plunger, coil stop and (especially) the coil sleeve is full of gunk.
          We are in the process of writing up a, much longer and detailed than we anticipated, overhauling of a pinball playfield.
          Included in that is a section on rebuilding the mechanics. It also has a section on dealing with sunken and lifting inserts. Please take a look at what we have so far and let us know what you think. If is work in progress as of this date (01/20/2021) so there maybe some parts that are not clear or misspelling. If you find any areas that need improvement, please let us know.
          -The Home Pinball Repair Team

  2. When I was looking for a site related to pinball repair, I found your site and sent a message.
    Because, I bought a junk electromechanical pinball machine and repaired it.
    Initially, the improvement was progressing, but at some point, no improvement was seen. It was.

    If you don’t mind, I would like to ask for your advice.
    We apologize for the inconvenience, and thank you for your understanding.
    I’m sorry if the meaning of the message is difficult to understand.

    Manufacturer name: Bally
    Machine name: DELTA QUEEN
    Year of manufacture: 1974

    [Machine condition]
    When the power was turned on and coins were inserted, the game did not start and the 00-90 unit made a vibrating sound.
    The vibration sound continues to sound until the power is turned off.

    1. We try to help out when we can, and in relatively quick situations, we try to. We hope you understand that it is difficult to do this given all the questions we have.
      With the symptoms you describe, there can be so many things wrong. ‘coins were inserted’ – Did the number of games go above zero on the free games wheel? Or did the insertion of coins immediately try to start the game?
      Usually, the first thing that starts up with an EM game is that ‘Score Motor’ on the bottom of the cabinet.
      If that does not turn, that is likely the place to start.
      ‘the 00-90 unit made a vibrating sound’
      By that, do you mean that the ‘ten’s’ score reel is not turning, but it sounds like the solenoid is trying to pull in?
      If so, it will need to be disassembled and cleaned by following our procedure.
      But all the reels should be re-setting to zero. The game cannot start until that happens. And the score motor should continue spinning until the reels are all at zero.

      It sounds like your problems exceed our time that we can spend to help you. Plus, with so many potential things wrong, it is tough to do by long distance. We have some links on our FAQ page to discussion groups where there are lots of (sometimes) helpful people willing to answer questions.

      We hope this helps.
      -The Home Pinball Repair Team

  3. Thank you for reading the message.
    After cleaning the 10-point relay, the vibration noise stopped.
    I will check all the contacts again.
    Since the flipper’s power is weak and the ball does not come to the plunger lane, I will continue to study repairs here.
    I came across a great site.

    1. That is great that you were able to troubleshoot it.
      There are people who approach EMs by troubleshooting the problems as they come across them. There are a large group of hobbyists who approach their pins that way.
      There is another school of thought, which is to go through and clean every contact in the relays and switches, including those on the reels and the Score Motor. This is what we do. But we do this because our games go out into the museum and we want them to work day in and day out. It is also risky, since if the person does not know what they are doing, they can create problems where there were none before.
      Going through the symptoms and finding the problems, like it appears you are doing, is a great way to start out. And for home use, it may work just fine.

      As to the weak flippers, it is more than likely you should rebuild them. The EOS switches are likely shot as are the cabinet flipper switches. Not to mention worn linkage and smashed coil stops. We suggest that you look here:

      And there is a good section on how flippers work.

      -The Home Pinball Repair Team

  4. Lots of great info and illustrations & photos. One correction is needed: Gottlieb score reels are Decagon, not Dragon. You ought to correct that.

  5. i have a 1964 gottlieb bowling queen the single digit scoring reel dosen’t record any points after hitting a bumper. I hear a humming noise and when i hit the target to change the one point scoring to 10 points it scores on the 10 point reel and the humming stops then the humming noise gradually builds again until another target is hit

    1. We have problems troubleshooting Gottlieb EMs since Gottlieb does not allow free distribution of their schematic diagrams. But there are certain common troubleshooting elements that we can fall back on:

      *Does the score reel work at all? The hum you are hearing might be the reel trying to activate? Or does it just not work with this bumper? If from the reel, the reel needs to be overhauled – instructions are in this section of pages.

      *The hum you hear may or may not have anything to do with the issues you are having. All pinball machines can hum while operating normally, especially EMs. The hum can come from the power transformer, or a relay that is on and is supposed to be on at all times. If this humming concerns you, then you will need to identify where it is coming from. If it is the transformer, that is (usually) normal. If it is a relay, then it will be important to determine if that relay is supposed to be activated while the game is being used. For example, in many pins, there is a coin door relay that is activated while the game is powered up and that relay can be annoying.
      It is also possible that a switch is closed, when it should not be, and that is activating a relay. That is not normal and needs to be fixed.

      *Switches do not (usually) activate solenoids like those in the score reel directly. The switch is (usually) low power. It activates a relay that can handle the higher power. The relay can activate a number of different solenoids. In this case, the solenoid in the reel should be activated and (usually) a solenoid to hit chime. In this case, the relay also activates the pop bumper solenoid. Sometimes these relays are setup in chains so that the pop bumper switch activates the relay for the pop bumper relay, and that relay then activates the single point relay – which then activates the reel and the chime.

      *Some pop bumpers have two switches. One activates the pop bumper solenoid. The other one activates the scoring when the solenoid powers up. This is common in some early Williams SS pins.

      Troubleshooting a problem like usually takes a while even with a tech who is familiar with the schematics and the design of the game. People like us, who work generally on games made by 4 or more companies, plus various generations of EMs and SS pins, it can take a little while. But we would test the following:

      1) Press the pop bumper skirt. What happens? If the pop bumper solenoid activates, does anything else activate? If yes and no, then that is where the chain is broken.
      2) Manually press the single point relay. What happens? Does the reel move? Chime work? If yes and yes, then the problem is likely between the two relays. Or a switch on the pop bumper.

  6. Hi,
    We have a 1977 Gottlieb Big Hit. It was working just fine until my husband replaced all the lights and rubber bumpers. When we turned it back on it starts up but runs through the 3 plays until it says game over. If we take the ball out we can reset it and it starts at game one but then once we put the ball back in it runs through the games again until game over (without any actual play). He didn’t touch that ball sensor when replacing the bulbs and rubbers so we are confused to what happened.

    1. Sorry to say, but this is a good one. When having an issue after doing something, usually (but not always) the problem is related to what you did. This should not be caused by replacing the bulbs, but it could easily be caused by replacing the rubber in the game.

      When replacing the rubber bands in the game, you are touching the ‘ball sensor’s, just not the one you are thinking of. It likely starts up when you put the ball in because the game cannot start without the ball.

      When replacing the rubber, there are leaf switches that touch the rubber bands. For example, the sling shots each have (usually) four leaf switches that touch the rubber. A tighter rubber might cause those switches to close. However, if that were the case, we would expect the sling solenoid to lock on – does it?

      There are usually other sensors that touch the switch that may not activate a solenoid. But those usually cause a point to be scored if closed. Are any points added to the reel prior to the game being over?

      Here is a link to the type of leaf switches that you have in the pinball machine. We would start by checking all of these that contact the rubber.

      It would also be helpful to listen as to what relays are activated in the game when it goes through all of the balls. Be sure to note each step that occurs. Any one of them could be the key to figuring this out.

      If that does not help you find it, please check back and tell us what you did and did not find.

  7. I hope someone can help because it is hard to find answers. I have a Gottlieb Abra-ca-Dabra that I had serviced last year – generally very well.
    One issue now is that my match doesn’t light up all the time, even though all the bulbs were replaced. Is there something I can check? it works maybe 25% of the time.

    Another issue is that when I had the machine moved to my house about a decade ago the company (a pinball mover) set it for unlimited games which I did not ask for – so now at zero games you can play. I think I know how to change that but can I do it safely? I think there is just a switch I have to open at the back. Can someone help me with this? Thanks in advance.

    1. This is the classic symptom of bad contacts. They can be dirty or worn. The first ones we would check would be on the lowest digit reel (if the ‘1’s are a fixed zero, ignore that).
      In this page:
      we would suggest disassembling the reel. You will remove that primitive circuit board that covers the reel. Then, be very careful, as there are a set of contacts that are held in place on the numbered reel. When reassembling, make sure it is put back on pointing in the correct direction or else you will get a match on the wrong number.

      Clean up that circuit board using the techniques outlined on this page, as well as the contact piece located on the reel itself. Make sure it is cleaned properly so that good electrical contact can occur.

      After that, reassemble, and see if it works.

      Sometimes, the lamp sockets can be flaky. If so, clean them as instructed here:

      Also, check the wires going to that circuit board on the reel. They can become frayed and cause intermittent issues.

      Hopefully, these steps will fix the problems. There could be other issues down the line, but these are the typical cause of what you are seeing.

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