EM Score Motor Adjusting & Repair

Cleaning and Adjusting the Scoring Motor of an EM Pinball Machine

Bottom panel placed in work area

The score, or scoring motor is frequently the focus of problems in an EM pinball machine.  On startup, it just keeps spinning.  Or sometimes certain functions do not work.  Most of the time, technicians attempt to identify and fix the contact that solves the problem.  But a better way is to overhaul the entire score motor assembly.

Note: Click on an image for a larger photo.

Getting the Score Motor to Work Perfectly

In order for the score motor assembly to work perfectly day in and day out, it will be necessary to disassemble the switches from the motor, clean and adjust every one.  This will proceed faster than expected, because it is much easier to do this than troubleshoot an issue with the motor.

This procedure covers Williams and Bally scoring motors.  Gottlieb scoring motor overhaul will be covered later.

Materials Needed
Screw Holding Bottom Panel to Cabinet

Understanding How the Switch Stacks Work

the leaf stack parts
Leaf Stack Parts

The leaf switch stack is made up of the following parts**:

*Copper leafs with a contact towards the end.  Each set contains two or three of
      –Stationary Leaf on the contact that does not move.  
         One or two of these.
      –Stationary Blade fixes the position of the Stationary Leaf.
      –Moving Leaf. One leaf that moves up and down.  
         This is the longest leaf.
*Several of these sets are usually placed on each other to create a Leaf Stack.
*Spacers that move Moving Leaf up and down.
*Paper Insulators that prevent electrical contact.
*At the bottom of the Leaf Stack is the Leaf Stack Contact.
The Leaf Stack Rides on the Scoring Reel.

The leaf switches in the scoring reel move up and down as the reel moves.  Some of the switches make contact when the leaf is down, others when the leaf is up, and many make different connections when the leaf is up and down. 

Grand Prix Score Motor schematic
Grand Prix Score Motor

**We admit that not every pinball person refers to these components exactly the same.  So we did our best to make this understandable.

Williams and Bally have pretty good schematics explaining what each switch on each stack does.  In this example, the score motor from a Williams Grand Prix is displayed (which is what is being worked on in these photos).  The first switch is called ‘Impulse Forward’ and has just one switch. The label indicates what the switch does, which is impulse (activate) relays #1 & #2.  This wheel has 10 notches, but the reel typically spins only half a revolution each time.  This relay is typically involved in scoring 5x points (50 or 500).  The switch closes as the Leaf Stack Contact gets pushed up.

Remove the Cabinet Bottom Panel

Location of Jones plugs

To make this easier, it will be necessary to remove the bottom panel from the game.  This is made to be simple by the manufacturers. 

Caution:  Be certain to unplug the pinball machine before proceeding.

1)  Set aside a clean clear table to hold the bottom panel.

Location of Jones plugs

2) Unplug the ‘Jones’ plugs.  There are usually a couple towards the back of the panel.  And a few more in the wiring harness from the panel going up to the backbox.  Pull up from the wafer.  Do not grab the wires and pull.
3) Place plugs from the wiring harness coming from the bottom panel, down on top of the bottom panel.
4) There are two or more large screw heads holding the bottom panel to the cabinet.  Loosen all of them so that the bottom panel is no longer held to the cabinet.
5) While checking to insure all wires are free and all screws are loose, carefully lift the bottom panel out of the cabinet and place onto your work area.

Overhaul the Williams or Bally Scoring Motor

Switches labelled

Once the bottom panel is placed in your work area, position yourself along side the scoring motor.

Label the switches so that they can be removed and then reassembled.  Take photos for reference.  Note that each stack of switches is held in position by two screws.  

Switch stacks being removed. Rubber band holding them together.

Check to see if the switches are accessible from both ends.  If one end is partially blocked by something like the transformer, then all the switches will be removed, except for the one closest to the transformer.

However, if the switch stacks can be accessed from both ends, then all switch stacks will be removed, except for the center two.

Remove the stacks one at a time.  When removing each stack, be careful to not let it come apart.  Immediately wrap the switch stack with a rubber band – locating the rubber band between the two screws. 

Note: The screws can fall out and be easily lost.  Either leave them in place and try to have the rubber band hold them – or remove the screws and carefully store them aside.

Depending on your setup, you will either be working on the one remaining stack on one end, or the two left in the center.

Some stacks removed.

Prior to proceeding, read the section on adjusting leaf switches.  It is important how to adjust a leaf switch properly.  Also note the section on cleaning the switch contacts.  

Pay particular attention to the section that describes the adjustment of the shorter blade that touches the stationary blade.  For these switches to work properly, the stationary leaf must be set against the stationary blade.  Moving the stationary blade changes the position of the stationary leaf.  Otherwise the stationary leaf will bounce around during game play.

Cleaning of the Switches

With the switch stacks out of the motor, it is relatively easy to access each switch and clean the contacts.  Our favorite technique is to use the Dremel and the 1/8″ Carbon Steel Brush 443.  Each switch contact should be nice and bright.  Follow up with 91% alcohol and a q-tip to remove any leftover residue.

If following this procedure, the first stacks to work with are the two left over in the center.  It is possible to remove one of those stacks to clean the contacts (wrap the stack with the rubber band!), then replace it for adjustment.

Adjusting the Switches

Switch stack on the score motor.

After the contacts are cleaned, note how the score motor moves and the switch stack moves.  In this photo, the switch stack is ‘up’ most of the time, then moves ‘down’ into the notches.  In this example, the switches open up at the top, them make contact when they are ‘down’.

Caution: Manually move the score motor in the correct direction.  The stacks always climb up a gentle rise, then drop off a ‘cliff’.  Moving in the wrong direction may destroy the switch and / or the motor.

Adjust bottom leaf

1) Using the switch adjusting tool and the proper technique, adjust the bottom leaf so that the leaf stack contact just barely touches the wheel or is slightly above the wheel at the low spot on the wheel.  We do not want much pressure on the wheel, otherwise parts will wear faster.


2) Next, adjust the bottom most moving leaf so that the spacer touches the bottom leaf.  It should not push the bottom leaf down very much, but it must touch.  

The force of this leaf down will push the leaf stack contact down just a little.

Adjust the shorter leaf to make contact.

3) Finally, adjust the shorter stationary blade up so that the two contacts meet and make firm electrical contact.  This leaf must make contact with the longer moving leaf.  But when the stack moves up, these two contacts must separate.


Contact Opens

4) Check your adjustments by rotating the wheel in the correct direction.  The leaf stack contact will ride along the wheel and push the stack up.  Ignore the switches that have not been adjusted and just look at the one you worked on.  When the leaf moves up, the two contacts must separate.  If they do not, then adjust the shorter stationary leaf back down a little bit so that the two contacts separate.

Repeat steps 2 – 4 for each of the remaining leafs.  

Contacts Up

Note that some contacts will occur when the stack is up.  When adjusting a lower set of leafs, while performing steps 2 – 4, insure that the upper shorter fixed leaf does not make contact when down, but does make contact while up.

Adjusting the remaining switches on the stack can sometimes affect the lower adjustments.  After completing all the adjustments, go back and review the stack for proper operation.  One may find that an earlier adjustment might need changing.

Also pay attention to the pressure of the Leaf Stack Contact onto the wheel.  If the downward pressure of all the leafs is too great, then the parts will wear.  It might be necessary to go back and lift up each of the longer leafs just a little.

First time through, this process may seem daunting.  Try starting with the smallest switch (least number of leafs) first.  Repeat adjusting your first stack.  After a couple of time, this will become much easier. 


After finishing up with one stack, carefully check its operation to insure that it is working properly.

Then attach the next stack in the order.  Repeat the above adjustment process.  Continue with each stack until all are cleaned and adjusted.

While the bottom panel is out, we recommend cleaning and adjusting the other relays.  Then just reassemble.    Enjoy that your score motor will work like the pinball machine is brand new and it likely will not give your problems for years to come.


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.

13 thoughts on “EM Score Motor Adjusting & Repair”

  1. Nice write up in cleaning and adjusting score motor assembly switch stacks.

    When I clicked on this, based on the title, I was hoping for information directly related to cleaning of the score motor. Not the switch stacks.

    Was looking for info on cleaning, and lubricating of the motor itself as well as the shafts and gears within motor assembly. Not switch stacks.

    Good general info still. Just title threw me.

    1. Thank you for your comment. Most of the problems encountered with Score Motors involve misadjusted switches. These need to be cleaned and adjusted. Far less frequent problems involve lubrications which are used at most sparingly.

      For example, with a Gottlieb Score Motor, the brass gears are not to be lubricated. Both brass and nylon portions should never be lubricated and are designed to be operated dry.
      On the bottom of the motor, there is a felt pad that should be lubricated with a couple of drops of oil, 3 in 1 will work fine.

      There is a lot we want to add to the website. We are about half way through doing a writeup on doing a ‘shop’ of a game and realized that it is a lot more time consuming than we expected. And we want to do a writeup on reading and understanding EM schematics – based on the number of questions we have gotten.

      But we will add to our list the need to overhaul and clean the motor & gears of the score motor.

  2. After I push the replay button on my 1964 Gottlieb Sea Shore the score motor will engage but more recently I have to continue to press and hold in the replay button hearing the motor make several turns before the score reels reset to zero and the first player light comes on. I seem to remember one short press and I would hear the score motor spin 1/3 turn, the reset bank click, and score reels reset to zero.

    1. We would have to observe the pin directly to be sure, but it sounds like one or more of the score reels is not turning freely. If after pressing the start once, one or more are not reading zero, that is almost certainly the case.
      If it has been a while since they have been cleaned, following our procedure on the reels will get them snapped back like they were new.
      What we have up there is for ~1970 or so Gottlieb. So your ’64 might be a little different, but not much.

  3. I had other issues with the score reels and they were cleaned and adjusted and work snappy during gameplay and generally reset nicely when hitting the replay button.

    If I hit the replay button on the coin door I see the score motor make a 1/3 turn and score reels reset to zero and the reset bank solenoid resets and player 1 lights up ready for a game.

    But not always on One pulse of the replay button. I hit the replay button and the motor spins 1/3 and then nothing. And I hit it again and then again and the start up sequence usually completes after two or three 1/3 spins or if I hold the replay button in for a two or three seconds and that also spins the motor a few 1/3 turns and then kicks in.

    And if I press the replay button again for a second player sometimes it might be just one press on the replay button but often a few presses or holding it on. So that’s why I don’t think it’s a score reels problem because after the score reels reset and then I push the replay button to make it a 2 player game I sometimes have to push the button several times or hold it in for a second or two.

    I thought maybe the score motor is not making good contact but I previously cleaned all the contacts and they look clean and gapped right. On the schematic it appears that when the motor turns it sends a signal directly to the D Reset Relay which resets all the score reels to zero and then another contact on the score motor engages the reset bank armature solenoid and the Start Relay on the Control Bank.

    Should the motor only take a 1/3 turn to get the start up sequence going or does it depend on the position of the score motor from the previous game. Does it have to make several 1/3 turns before it finds the “home position?” Machine works great otherwise.

    1. The score motor has ‘home’ positions. Those can be found by looking at the score motor. Generally, one disk has just a few indentations – usually three. When it has come to rest, a switch has reseated in that indentation and that switch is now open and the motor has reached home.

      But the motor will continue turning until everything is reset. When those resets are not achieved, the score motor will continue turning. This is the major reason that EM’s fail – with the score motor continually turning. Most people inaccurately blame the score motor when it is something else – usually a reel – that is not resetting. Of course, there are lots of other things that have to reset, such as the ball in play, the player up, etc. that have to occur for the score motor to be ‘happy’ and come to a rest.

      If the score motor is moving to the next ‘home’ position and nothing is happening to any of the score reels, then that means one of the switches on the score motor is not making contact, or the relay it activates is not making contact. From your comment, I think you understand that.

      It sounds from your original description that the score motor turns and comes to a rest (presumably at home), but the pin is still not reset nor ready to start a game. That means something has not occurred in the reset process – an admittedly rather obvious statement.

      But troubleshooting what is not happening is very difficult if not impossible for us to troubleshoot without being there and observing the pin in action. Please let us know what you find out.

  4. Thank you for your analysis. I’ll continue to hunt this down. I’ll look at the schematic some more. I find the combination of reading the schematic and visually observing the the relays has solved problems in the past.

  5. Thanks for the concise information regarding making sense of the score motor in my captain fantastic em bally I just purchased. I have just finished going through the all the switches in the order presented in the write up and because I found several switches way out of adjustment feel confident that a major hurdle in getting this machine operational has been passed. Thanks again for putting this very well written guide to restoration available

    1. Thank you for the kind words. It is nice of you to post them.
      We are always looking for ways to improve the site. If you have any suggestions, please send them to us.
      -The Home Pinball Repair Team

  6. Hello, I’m new to em machines. My Bally Time Zone was working just fine until I unplugged the two connectors in the back box in preparation for removing. I didn’t remove back box at this point, just unplugged then plugged back in. I started a new game and now the game never ends. Ball drains out and new ball is kicked out for playing. Never ending supply of balls. Any ideas?

    1. There are all sorts of possibilities but we should focus first on the one thing you did – which is to unplug, then plug back in the Jones plugs.

      First suggestion is to unplug those plugs again and plug them back in, and carefully insure that they are fully seated.

      If that does not work, then unplug each plug and inspect the wiring connection. This 50 year old wiring harness can be damaged. You want to insure that every wire is connected to a pin and only one pin, without any strands of frayed wire not connected or touching other bare wire.

      The third suggestion is to remove the playfield glass, start a game, remove the pinball and then tilt up and carefully lock the playfield into place with the bar that is used to hold up the playfield.

      Try pressing down on the switch that the pinball ends up on when it drains and listen to the clicking going on. That will indicate which relay is being activated.

      The fact that the ball is sent back up to the shooter likely means that the switch is working, but that one of the contacts on the relays is not working – coincidence with the Jones plugs? Or is the relay closing but the signal is not being sent to the ball advance disk?

      Do you have the schematic?

      At section 8H is the outhole switch. When that activates, the outhole relay is activated. That is what you should hear when ball drains into the outhole. The outhole relay should advance the ball index relay at F9. Then the ball disk has to turn located in 5B.
      The relays should be labelled as to which one does what. If the outhole relay is activated, then check to insure that the ball index relay also activates. If both of those work, then the ball index disk should turn.

      At that point, it will be time to figure out where that chain breaks down.

      If you cannot find it, please get back to us.

  7. Hello,
    My Gottlieb Big Indian score motor won’t reset, I checked the proper sequencing and everything is working as it should ( except the Control Bank) reset. I have to manually push the reset bar to get the score motor satisfied (stopped). The motor stack switch 4C makes as part of the start up of the game, then closing the U relay which in turn resets the (Control bank) which does NOT happen here !! I can manually push in the U relay which works fine, then I can play a normal ( Game ) s PB1 , PB2, PB3 etc all 5 balls per player, then the QB game over relay kicks in as it should. It will also match at certain times. So by pushing the ( Start relay button, this locks In through its own switch and motor 2B starts the motor running. Then the SB relay is actuated by switches on motor 1A and motor 3B through a switch on the ( S ) relay. So at this point the SB switch is tripped, the reset relays ( Z2 and Z1 do their job by resetting the players score reel to the ( 0 ) position. When Z2 falls out after the score reel reset and then Z1 stays energized until the 1st and 2nd player reels get reset through motor switches, now at the same time the ( Player ) unit steps up to its zero position via motor switch 1A in series with the SB and run off switch on the player unit PB5. Now here’s my ISSUE! The Control bank should reset via motor switch 4C thru a switch thru the U relay…., to NO AVAIL! Sorry for being long in the tooth on my explanation, but I’m totally frustrated after many hours of cleaning and adjustments of switches and stepper units / cleaning 16 score reels / Jones plugs etc. btw I do not have The Gottlieb schematics, I’ve been getting a lot of info off the internet. I do understand most of the analog logic of these EM ‘s but I’m at a loss at this point, anything you folks can recommend will make me eternally grateful! Thanks in advance.

    1. Sorry for the delay in responding. We were shut down for vacation and are now trying to catch up.

      “btw I do not have The Gottlieb schematics”

      That is the first think you need to rectify. We don’t have a schematic for it either. Gottlieb protects their assets and do not allow people to post schematics free online. The Pinball Resource has a license to reproduce the schematics. In order to fix and maintain a pinball machine, you must have the schematics.

      We can make some guesses without the schematics and look at a few other machines from that era, but we cannot be certain. Some of the common things to look at:

      “I can manually push in the U relay which works fine..”. By that, when you press in the U-relay, the control bank resets? If so, that means that the coil is OK and everything is getting power. Please note that in many of these games, the ‘Reset Control Bank’ solenoid runs off of line voltage, so that power is extremely hazardous.

      On the only Gottlieb schematic we have right now, the 4C third switch on the score motor is what activates the control bank reset. There is also a 1/2 A SB fuse in that line. Then there is also a SB Armature switch. This is a switch on the control bank relay arm that closes when the relay bank has been activated. So all you need to have to make that control bank reset on THIS PARTICULAR MACHINE is for those three things to be good. But since we don’t have a Big Indian schematic, we cannot be certain that the same is true for you – as we don’t have a ‘U-relay’ involved.

      Please get back to us to let us know how it goes.


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