Operation and maintenance of EM pinball

Degital game wurk by mazik, mekanikal by magnetischm. Magnetischm guud, mazik baad.



This quick guide is meant to give general information on EM games and fixing their typical problems. There are hundreds of different machines, so it is not possible here to concentrate on game specific problems. Tips on fixing modern solid state games are here or on APZ's pages (in Finnish only).

What is an EM pinball?

Every pinball game found today in a bar or an arcade is a solid state machine. This means that all game features are controlled electronically by a microcomputer. Electronic control makes complex sounds, flashing lights and graphics displays possible, along with an interesting game strategy.

Before 1978 the games worked without any computers. In these EM, or electromechanical games sound came from clicking relays and solenoid operated chimes. Score was displayed on rotating reels, and the lights didn't flash much. Gameplay was quite simple, compared to games today. Anyway these mechanical machines sucked coins from players pockets and offered thrills and joy as much as todays games. Even if they do not appear on location anymore, there are still plenty of EM games around, and also many hobbyists keeping up the tradition.

Most notable manufacturers were Gottlieb, Williams, Bally and Chicago Coin. The Gottlieb games are highly valued by collectors, but my opinion is that many Williams and Bally games were more interesting to play. The golden age of Bally was the early 1970's, and so Ballys of that age are very desired. Chicago Coin is a little less known and not so popular manufacturer, and its games are harder to find.

EM pinball components


An EM pinball works completely without electronics, just by relays, motors and solenoids. Faults are quite easy to troubleshoot and fix, even without a schematic diagram.

If you are completely unfamiliar with EM technology, here is a short description of various parts found in an EM machine:


A switch is made of two metal leafs, that have a contact point on one end and a solder lug on the other. The leafs are separated by bakelite spacers. One leaf remains stationary while the other moves and may or may not contact the other, which then controls whether current flows through the switch. This kind of switches are used practically everywhere in a pinball. Rollover lanes on playfield, behind rubber rings, flipper buttons etc. Also on relays and score motors.


A lamp is a component that... OK, you probably know. EM pinballs used almost exclusively #44 type lamps, or 6.3 V / 0.25 A / BA9s bayonet socket. It may be wise to replace those with #47 lamps, that generate less heat, at least in backboxes where the heat may make backglass paint to flake or fade. Also in bumpers and near plastics, the cooler bulbs prevent plastic warping. They also help you save energy!


A relay is a small device with an electromagnet, that makes an armature move. The armature in turn moves one or more switch leafs. There may be both normally open and normally closed switches on a relay. Sometimes even both types of switch may be combined to a changeover type of switch.

Nearly every function in an EM pinball has its own relay. The relays have labels beside them, that tell the relays name, for example "10 POINT RELAY", "TILT RELAY", "EXTRA BALL RELAY". Some Gottlieb games label the relays only with an identification letter, and you need a schematic diagram to explain those letters. Fortunately the same letters were used in many games, so they became quickly memorized.

Some relays have two coils. Electric pulse to the other coil moves the relay permanently to one position, while pulse to the other coil moves the relay to another position. These latching relays can sometimes be quite difficult to adjust, especially the small Gottlieb model.

Relay bank isa a series of latching relays, that are all reset at the same time with a large solenoid. Nearly all EM machines have one or more relay banks. The bank can reset at the start of game, and thus have relays like "Start", "Game Over", "2 can play" etc. For features that reset at start of every ball there may be another bank with relays like "A-B-C-D", "double bonus" etc. Bank relays are bigger than normal relays and do not fail often. But the reset mechanism does hard work and may wear and start sticking.


A solenoid is an electromagnet coil, that has a moving metal rod (a plunger) inside. When the coil gets power, it pulls the plunger in. Flippers and bumpers work this way both in EM and in SS games. On EM games the solenoids are also used in many other places turning some switches. Sometimes a solenoid has two windings, that are needed if the solenoid must stay energized for long time. The heavy power winding only gets a brief pulse to pull the plunger in, and after that a switch directs current through a lighter holding winding that is powerful enough to keep the plunger in.

Score motor

The "heart" of an EM pinball is the score motor. It is an electric motor that has notched metal or plastic discs or cams operating many switches while the motor turns. Nearly all functions in an EM game are controlled by the score motor. Many faults cause the motor to keep turning endlessly, but very seldom is the problem at the motor itself in these cases. The score motor is needed for example in scoring 500 points. A playfield switch energizes the 500 point relay, that turns score motor on, a motor switch gives 5 pulses to scoring reel, and another switch then turns off the 500 point relay. This is how most game functions operate.

Gottlieb and Bally used a motor with vertical shaft, having switches in many layers on top of each other and on every side of the motor. Adjusting or checking the bottom switches may be difficult. Williams used motors with horzontal shaft, and all switches in one row. They are easier to clean and adjust.


Units are counters operated by solenoids. Some units have one solenoid, they rotate a step at a time in one direction only. For example, a match unit, that selects the match number at end of game is this kind of unit. Some units have two solenoids, one turning the counter forward and the other backward. A bonus unit operates in this way, advancing bonus with the forward solenoid and scoring bonus with the backward solenoid. It is possible for the unit to have also a reset solenoid. A ball count unit is reset at start of game by a pulse to the reset coil, and stepped up at every ball by a pulse to the advance coil. It doesn't need to be stepped backwards. There might be 3-6 different units in an EM pinball, depending on how complicated game it is. An unit may have a dial attached, such as the credit unit that shows the number of credits in addition to keeping track of whether there are any.

Score reel

A special case if unit is the score reel or drum unit. They are used to indicate players score. A score reel has a plastic drum that is painted with numbers 0-9. A solenoid moves the reel one step at a time. Most EM machines have 4 score reels per player. Older games showed the score directly as 0.000-9.999 but then the points were made to look bigger by adding a zero, to get scoring of 00.000-99.990. This added zero did not require a score reel however, so there were still four of them. Some later Williams games had 5 moving reels per player, for scores up to 999.990, while some older games got along with 3 reels and a lighted "1" in front of them, for up to 1.999.

Still older games, in the 1950's and earlier, did not use score reels but normal counter units instead to advance lighted number on backglass to indicate score. Scoring then was badly inflated, a slingshot scored 10.000 points, and the scoring usually were indicated in millions!


The playfield is basically alike in all games from the 1940's up to today. The EM pinball uses similar devices on the playfield as the modern SS games. But the playfield itself is a single level, without ramps or wireforms. But present are the flippers, bumpers, slingshots, drop targets, stand up targets and rollover lanes. Solenoids in an EM game operate on AC and are much weaker than todays powerful DC coils. Thus the playfield angle is much shallower, and the ball speed feels slow for a player who has accustomed to modern games. Accuracy is more important than speed in these games. But when you clean and wax the playfield, use new good quality rubbers and make sure the flippers are in good condition, the games are fast enough. Note that EM games use exclusively white rubbers. The black ones are not suitable for EM games, they are not bouncy enough. If you are desperate for more speed, you might try moving the 24V power lead at the transformer to HIGH TAP, that gives a few volts more. Be prepared to replace broken targets and loosened posts on the playfield then! The high tap is supposed to be used in locations with lower than normal line voltage. In Finland, and also in many other European countries, the voltage was adjusted from 220 volts to 230 volts at the end of 1980's, so the games already got a little boost and the high tap is not recommended. Plastic posts on playfield are not bolted through the wood as in newer games, so they tend to loosen when hit by the ball from high tap powered flippers. If you want a fast machine, buy a newer game.

EM fixing

To repair a broken part, you must know how it works! If possible, examine your EM machine already when it is working, not only after it breaks down. Try to explain to yourself how everything works. You may visit an EM collector, who will probably gladly show you his machines and explain their operation. There are no major mysteries in an EM machine, so just looking at the stuff usually gives you an idea how it works. One thing to keep in mind is that the game was working when it left the factory. So if there are visible modifications somewhere, for example some unit levers return spring has been made more tight by bypassing a part of spring, you can be sure there is some other problem in the unit, that is only hidden with the spring adjustment. Usually these problems come from dirt. Try cleaning everything, and then maybe it works without tightening the springs. It is always best to try and keep everything as close to original shape as possible. Often there is a similar part or unit somewhere else in the game. Does that work? What is the difference between working an non-working units? When you take stuff apart, keep notes or take photos so it is easier to put them back again. Do not rely on your memory only!


EM, much like SS pinballs do not require much lubrication! By excessive lubrication, you cause more problems than you fix, so the rule is: dont lubricate if you are not sure. All handy oil sprays, such as WD-40 or CRC do help for a while, then the light parts vaporize and a sticky gum is left. Also the oily parts collect dust and dirt.

Only points to lubricate are those that have to metal surfaces moving against each other. Slingshot lever hinges, and some unit lever bearing points are examples of these. So is the score motor gear train. Solenoid plungers may never be lubricated!

If against all warnings someone has emptied a can of WD-40 into your machine, a quite tedious job awaits you. You have to take practicaly everything apart for cleaning. Use alcohol or isopropanol. Take care to get enough fresh air while using this stuff!

Switch adjustment

Before adjusting any switch, make sure its mounting screws are tight! They loosen in time, affecting the switch leaf spacing. An old EM machine may have really many loose switch stacks.

There are switches evrywhere: on playfield, relays, units, score motor and so on. Proper operation of the game depends directly on the operation of those switches. It can be thought that when every switch is adjusted properly, the game functions perfectly. But this does not mean that you should have to adjust every switch in an EM game after buying one. The golden rule is: don't fix a working part!

As the switch operates, there is a little spark between contact points. This wears the contacts eventually. Playfield switches may get bent to wrong position as repeatedly hit by a ball. Switches in an EM game have usually silver contact points and they can be cleaned with a contact burnishing tool. (Solid state machines have gold plated switches which you should never burnish) Adjustment of the switch is always done by bending the stationary leaf. Of course, if a moving switch leaf behind a rubber ring has bent out of shape, it is OK to straighten it. The actual adjustment should however be done on the stationary side. Try adjusting the switch so that when operating, the stationary side moves just a little bit with the moving leaf, this makes the switch clean itself a little at each operation.

Adjustment is best done near the switch stack, so that the tension of the leaf is not changed much. Keep power turned of when adjusting switches!

Flipper EOS switches, or the switches that enable the holding winding when flipper is up, are adjusted so that there will be about 1 mm gap between points when the flipper is up. Do not hold the flipper up manually, it may end up in a different position than when operated by the flipper coil and you may adjust the EOS improperly. Always check after adjusting! The EOS and flipper button switches pass large currents, and are made of special tungsten alloy. But still they need burnishing from time to time. They directly affect flipper power, so it is a good idea to keep them in good shape. If an EOS switch fails to open, the flipper coil will soon burn. Putting a 3 amp inline fuse at the EOS wire prevents damage in this case.

Never use contact spray on EM machines! It is meant to be used on small current tin or gold plated points. Large current switches generate sparks, that make chlorine out of contact spray. That then reacts with silver on switch points, forming silver chloride, a white powder like stuff that is an insulator and prevents switch operation. Just use a contact burnishing tool. Do not use sandpaper, it tends to leave dust between points.

Relay adjustment

When adjusting relays, first make sure you know how the relay works and only after that begin adjusting. You should be able to operate the relay manually in a way that corresponds the normal operation of the relay so that you can see how the switches work. Especially the small Gottlieb relays are sometimes very tricky to adjust. Make sure the switch stack mounting screws are tight. Then adjust the non-moving leafs so that the relay works. After some practice you will learn to see if the relay is OK by just looking at it. The main thing is to adjust so that all closing switches are clearly open when the relay is unenergized, and when operating, ne non-moving switch leaf slightly follows the moving one. If the switch points look worn, burnish them. It can be a little tight spot, be careful. Remember: no contact cleaner!

Especially Bally EM relays sometimes stay on even with no power. This is because the relay armature has gotten magnetized. Repair that with a hammer! Remove the armature plate, put it onto a solid place, bang with a hammer a few times. This removes residual magnetism, and the relay is good for another twenty years.

Some relays, typically HOLD or LOCK are held on for long times, or always when the game is powered on. They may get quite warm or even smoke. Eventually the hot coil can get partially shorted, that increases the heating even more. Usually you can cut the wire from the relay coil and bend the switches so that the relay is "always on". This will end buzzing and heating for good. Only effect is that the game may not go into Game Over even if you turn power off. Of course you can always replace the relay coil with a new one, that then takes care of the problem for another 20 years. Be sure to use a proper coil, one that is meant to be continuously on.

Nearly all EM relays operate on AC power. They must have an AC coil, that can be recognized from a copper ring at either end of the coil pole piece. DC relays do not have this ring and if they are operated on AC, they will buzz and work unreliably.

Score reels

Faults in score reels naturally cause the scoring to be erratic. Also it might happen that the game refuses to start. A common problem in EM games is that when you start a game, something happens at first, but then the score motor just keeps on running and nothing else happens. The game must get all score reels to zero position before starting. Score motor gives reset pulses through a reset relay to reels, until they are at zero. Now, if the zero position is not detected properly, the game keeps on trying to reset the reels indefinititely. This problem can be caused by either the reel not moving at all, staying at a non zero position, or then the reels zero switch is out of adjustment. Actually, there are two switches that change state on zero position. One switch opens preventing the reel getting any more reset pulses when it is at zero, the other closes to notify the game logic that the reels are all at zero (the closing switches of all reels are wired in series).

Besides zero position, the reel also senses its "9" position to be able to carry scoring over to next higher reel, for example if the tens reel is at "9" position then the next pulse on ten point relay activates both tens and hundreds score reels.

Also there is usually an EOS switch on the reel solenoid. This ensures that even a short pulse from playfield switch advances the reel properly. It functions as follows:
- ball hits 100 point switch on playfield
- 100 point relay pulls in, keeping itself on thru its own switch and the 100's reel EOS switch
- 100 point score reel solenoid pulls and when it is completely done, the EOS opens and 100 point relay drops out removing the reel solenoid power
If the EOS switch fails and stays open, it is usually not noticed. Some points may not be scored, if a ball just touches a switch. But if the switch stays closed there is a danger that score reel solenoid stays energized and overheats, melting the reel itself at the same time.

Score reel position is also sensed for replay scoring and number matching. The reel has a circuit board, that has segments for every position. A wiper shorts these segments to common signal according to reels position. If the board gets dirty, the game may not award replays at high scores or on match. Clean the board, check that the wiper spring has enough tension, and you may also use light silicone oil on the board to reduce wear. Do not use WD-40!

Never try to turn score reels by hand. You may crack plastic parts. The only way to move the reel is by pushing the solenoid plunger manually. Many reels have a little plastic pin on the backside, with which you can move the plunger.

The plastic reel, like everything else in pinballs, gathers black flipper dust. The reels must be cleaned every now and then, as also the backglass inside. Be careful. The black labeling can come off the reel. If that happens, try touching them up with a Sharpie pen. Do not use heavy cleaners.


Solenoid operated units are used in many places. A common problem is sticking of the unit, that then causes other problems, bonus not advancing, balls not counted etc. The resetting units may not be reset completely. Game might begin at ball #2 or something like that. Usually it is again dirt that causes these problems. So take the unit apart, clean it and put it together again.

When taking the unit apart, first set it to zero position. Mark the wiper position on the contact disc, if any. Remove the reset spring, which is the big spring around units shaft. Count how many turns the spring should be tightened. Then remove the coils. Clean the plungers and replace coil sleeves. Remove nut from shaft end and pull the wiper system out. Clean the contact blade with fine sandpaper. Wipe the sand and dust off with a cloth. Clean the shaft. Put everything back in the opposite order you removed them. Hopefully you made notes or took some photographs! Wind the reset spring with as many turns as you counted when you removed it. You may put very little silicone oil on contact disc. The unit should now operate smoothly and accurately. If it doesn't always reset properly, add one more turn to the reset spring. Check that the wiper contact points hit the contact disc points in the middle. You may move the disc after loosening its screws.

Newer machines use a small Match unit, that has two small circuit board discs with wipers. Insted of solenoid, it has a normal relay coil stepping it forward. Common fault in these is breaking of the plastic lever that moves the ratchet. It is difficult to fix otherwise than changing the armature piece.

Score motor

Nearly all EM pinballs funtions depend on the score motor. Strangely, the motor itself or its switches does not usually fail. Some switches need burnishing every now and then, especially those carrying large currents, for example relay bank or drop target bank reset switches. Switch stack mounting screws must be tightened sometimes, but other than that the motor doesn't need much service. A drop of oil to the gear train is not a bad idea. Typical problems caused by incorrect adjustment of score motor switches are: outhole does not kick ball out even if its relay operates, 500 point switch only gives 400 points, bonus is sometimes scored two steps at a time. All these are caused by too large gap on switches, or dirty switches. To adjust, first find out what switch is it that needs adjustment. Remember: dont fix that what is not broken! If you don't have a schematic, you can narrow the search by thinking a little. The switch for 500 point scoring is one of those that give 5 pulses per motor cycle. Outhole operating switch is one of those that operate near the end of cycle. A visible sparking at motor switch is a sign of misadjustment.

A common problem, score motor just keeps on running, is not usually the motors fault. Some relay that starts the motor, stays energized. Find out what relay it is that keeps the motor running, and why it stays on. But if the motor runs improperly and tries to stop in the middle of cycle, you should check the motor switch that keeps it running thru the cycle. The switch is in the stack that changes state at motor home position.