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This page is consantly changing. I will add more information as I am reminded of it through working on games or as I remember it.
Never work on a pinball machine when it is powered up - always remove the plug from the wall before opening a game. Do not attempt repairs unless you are competent to do so. You may cause more damage than you are attempting to fix. Please remember, electricity can kill.

Before stripping a component in your game, and at various stages of the process, take pictures as a reference. They can be very useful. If there is more than one of a component in the game, go through one at a time, and use the other for reference if you forget a stage whilst reassembling. Always use a container for removed parts, losing a vital part can be very frustrating. A magnet on a stick can be very useful to retrieve dropped screws etc. When removing springs, spring clips and other parts which could fly off, hold the magnet close as you remove them, it will catch any that try to  escape. If they succeed, sods law says they will be lost forever.

Never use contact cleaner in a game, it will ruin the contacts and is a fire hazard. WD40 is not a lubricant, it is a freeing agent. If a component is seized, stripping and rebuilding it is the recommended course of action. The only places in a pinball where oil should be used are where there is a moving metal to metal interface. Everything else should be assembled dry. A wipe of lubricant on stepper rivets is adviseable.

A worn or rusty ball will wear out your playfield very quickly. New pinballs are very cheap, so fit new ones regularly. A game that has dirt and dust inside will transfer the dust to a ball, which will wear the playfield. Make sure your game is clean inside. Vacuum it or blow it clean with an airline.

When working on the underside of a propped playfield, cover the motor board components with a towel or similar. Then, if you drop anything, it will be easier to find. It will also stop solder that occasionally falls, as you are soldering joints, from falling in to the motor board mechanisms. A splash which lands on a switch stack can easily short a few switches, this will cause the game to malfunction, and can be hard to locate.

The end of stroke or EOS switch.
Many relays in EM games have a switch on them known as the lock in switch. When the relay is energised, a pair of contacts on it close to make a circuit which feeds the energising coil, causing the relay to lock on. The only way that relay can de energise is when another switch in the lock in circuit opens. That will usually be a switch on whatever unit the relay is operating. The switch is called the end of stroke switch, because it opens when a coil plunger is pulled all the way in, at the end of its stroke. The idea behind this design is to allow the unit the relay is operating to have a full cycle, no matter how short the switch that energises the relay is closed for. A ball passing over a rollover or other scoring feature may only close the switch for a relatively short time, not enough to register the score. Locking the relay that steps the score unit will make sure the score is properly registered, even if the scoring switch could not do so. Once the score unit coil plunger has made its full stroke, it opens the EOS switch, opening the circuit to and de energising the locked in relay. The only down side to this design is when the unit the locked relay is operating doesn't work for some reason. Maybe the coil goes bad, or a soldered joint on a coil comes loose. Whatever the reason, if the unit doesn't function, the locked in relay is stuck energised. It will soon overheat and burn out. If you are playing a game and suddenly hear an unusual and loud buzzing, turn the game off and investigate the cause. It could be a relay locked on by its own switch and there is no way of de energising the coil.
There is normally an EOS switch on the replay unit, operated when the step up coil energises. It fires the knocker to signal a replay won. If the knocker in your game doesn't work, check this switch is clean and working.

Zero position or max position switches. These are commonly found on stepper units. There is one of each on a replay unit, to tell the game there are no replays left and it needs a coin to start a game, or to tell the unit it can register no more replays as it is at the maximum position. The switches, in this case, will open at the appropriate position of the stepper, and open the circuit that would normally step the unit up or down. Bonus units often have a zero position switch, and sometimes a maximum position switch. Again, they control when the step up or down coils can energise. If you want to set a game to free play, you need to make sure the switch that would normally open when the replay unit is a zero doesn't open. This will fool the game in to thinking there are still replays registered, and it will continue to give games from the replay button, even though there are no replays to use up. If your game won't count a bonus when the ball drains, check the zero position switch.

Trough, outhole and shooter trough switches. Older replay games with manual ball lifter plungers and five balls have a ball trough which has several trough switches and a ball release coil. The trough switches count balls returned through the drain to determine when all five balls have been played to end the game. On Gottlieb games, trough switches three or five end a game by the last ball closing the switch, but there must be a ball sat on two or four for this to happen. Games that are five ball and not adjustable have only trough switches four and five. On games that can be set for three or five ball play, two pairs of switches are used, trough positions four and five, and positions two and three. Which pair are used will be determined by whether the game is set for 3 o 5 ball play. The release coil will energise when you start a game to release the balls to the lifter, and will stay energised until the ball is shot and points are scored. These coils often buzz, it is normal and should stop when the first ball scores points.
Manual ball lift add-a-ball games still have a ball trough but require only one ball in the game. They have a ball count unit which the trough switches step down. When the ball count unit steps below the one position, it ends the game.
On single ball games with a ball launcher coil, the outhole switch tells the game when a ball has drained and is ready to be fired to the shooter lane.  A game won't start if there is no ball in the outhole. These switches can often get caught when dropping an opened playfield, and will cause the game to malfunction if the gap is altered or they are dirty. As the ball is fired to the shooter lane, it passes over another switch which will step the ball count unit and switch on some playfield features. If this switch isn't functioning correctly, some playfield features may not work and the game won't count the balls properly.

Flipper EOS switches. These switches have contacts that are made of a very hard material and they need to be cleaned with a good quality file. Flipper coils are of a different design to most other coils in a game. They are two coils wound on a single bobbin. One coil is a low resistance and therefore high power coil. The other is a higher resistance and lower power coil. The high power section would quickly overheat if a flipper was held up for any length of time, so when it is, the lower power coil is connected in series with the high power one, reducing the current draw through the coil assembly, allowing the flipper to be held up to cradle a ball. In most games, the EOS flipper switches function in a different way to normal EOS switches. When they are closed, they allow the circuit current to run through the high power coil and through the switch, giving the flipper enough power to shoot the ball back up the playfield. When the flipper coil plunger is nearly fully pulled in, it opens the EOS switch. This forces the current to take path from the high power coil and then through the low power coil, reducing the current draw. It reduces the heat build up in the coil, but reduces the flipper strength. It is still enough to hold the flipper up, but is not enough to shoot a ball. If your flippers are very weak, it could be because this switch is not adjusted correctly, or it is dirty and not conducting well. If the EOS switch does not open when it should, for any reason, and you keep a flipper button pressed, the coil will overheat and burn out very quickly. The flipper button switch contacts are also made from very hard metal, and they too need a quality file to clean them.

Flippers. On many games, the flipper mechanism includes a link made of some material. Very early Gottliebs are metal, later Gottliebs and Williams / Bally use a fibre link, similar to Bakelite. These links are connected to the coil plunger and the flipper pawl using roll pins. Over time, the pin elongates the holes in the link which leaves the mechanism with a lot of slack. New links are available, sheet fibre is also available. You can either buy new links or make them, but that slack needs to be removed if you want your flippers to work correctly. Check the usual parts for wear / damage and replace anything worn. The white Nylon bushes often crack across the mounting flange. This allows the flippers to move side to side, and can cause them to drag against the playfield, causing commonly seen wear marks. Replacement bushes have a thicker flange to prevent this. When setting the flippers, I usually try to use the light areas of playfield timber to match where the factory set them. The surrounding timber has darkened with time, but where the flippers have covered it, it has a lighter appearance. Set the flippers  by gently piching the pawl bolts to hold the flippers steady, but still allowing them to adjust. Set them in the up position by holding the coil plungers fully in, matching their positions, and then fully tightening the pawl clamp screws. They can be adjusted in the down position using the stop brackets. Make sure they are clear of the playfield and have a little end float. Use washers as shims to give the clearance between flipper and playfield if needed. Many 2" flippers need to be double rubbered to prevent them from cracking. The bats were designed when games used a 1 1/8" ball. When that changed to 1 16", it allowed the ball to hit the plastic bat as well as a single rubber, so another was added to cure the problem. Williams cast alloy flippers do not suffer from this problem, and look much nicer when polished or powder coated.

Switch stacks. The Bakelite spacers used to space switch blades in switch stacks will shrink if the game has been stored in less than ideal conditions. If they have absorbed moisture, they will shrink as they dry out. A pinball machine needs to be housed in an environment that provides a stable temperature and fairly constant humidity. The arcades, pubs and cafes where most spent their early days were perfect for the job. Your home is also an ideal place. A garden shed, unheated outbuilding, warehouse or barn is not. Many games were put in to storage at some time in their lives, so the Bakelite spacers in the switch stacks may have shrunk in a lot of games. Obviously, if the stacks are not tight, the switches can go out of correct adjustment, may slide in an arc so they are no longer parallel and the contacts will no longer make accross their full sufaces. A good way of assessing the general condition of a game is to check a few of the switch stacks. If the screws you check are tight, the game has been stored well, and it is likely all the rest of the stacks will be OK. It is still worth checking them all, even if the first few are tight, just to be confident nothing has been missed. If they are loose, you can turn the screws a 1/2 turn or more, probably all of them will need tightening. It doesn't take long, and should be done before any contacts are adjusted. The screw nearest the contact should be tightened first, and then the one nearest the solder lug. They are small screws, so only need pinching up, too much force could easily strip the threads or shear them off. Whilst doing this, it gives an ideal opportunity to check none of the switch solder lugs are touching each other, and to check the solder joints are good. A gentle tug on each wire will usually show up any joints about to part. Any wires frayed near the solder joint need cutting back and resoldering. If the core is showing a bit near the lug, the cloth wiring can usually be eased along the core so it is tight up against the lug again. Some games, mostly Bally, have a plastic sheath on the wire and lug, usually on every other one, as a secondary method of insulating the lugs. It has often moved up the wire and will need re seating. Switch blades in some stacks have a Nylon spacer fitted, to allow a pushed blade to move another. These sometimes fall out. They can cause faults in game operation and the missing spacer can be very difficult to spot. Finding it in the cabinet can be of help, at least in determining the length for replacement. Finding the blade it has detached from is not so easy. A good eye and some logic in working out how a switch stack should work will usually find it, but it will require a thorough inspection of the switches in the game. Replacement spacers are available, in various lengths.

Stepper coils. The brackets holding these coils are often loose. Check and tighten the screws if they are. There is often meant to be a curved spring steel washer between the coil body and bracket, put there to stop the coil 'chattering' as it works. It is common for these washers to be missing, lost or forgotten when a coil was removed to replace a sleeve or some other job. They do need re fitting, and are reproduced.

Missing screws and other components. These have often fell in to a game as it is played, as they can come loose due to the vibration a game produces. EM games were designed to resist this vibration, with anti rattle star washers used on most screws. These got lost as the games were repaired and serviced, so the screws vibrate loose over time. Contacts can wear away or fall out of switch blades. Labels come loose from relays, steppers, score reels. All sorts of small parts can end up in the base of the cabinet. Some work their way under the motor board. Before vacuuming the cabinet clean, sift through the debris to recover any useful parts there may be. Lift the motor board and check under it as well. Recovering a few screws, washers or other parts can save a lot of hassle finding replacements. The US games use AF threads, it is not easy to find new ones now everything is metric. A contact found can give an indication that one may be missing from a switch blade somewhere in the game. It may have been replaced, but if you have an intermittent fault, it is worth checking for a missing contact. Contacts that are loose in the switch blade will also give intermittent faults, and these can be very difficult to find. Replacement contacts are available in two sizes, light and heavy duty. They have tits which can be lightly peened over the blade, or they can be soldered to it or both. Replacement blades can be obtained in light, medium and heavy duty. They are long enough for all applications, and can be cut to length. The blades used in relays are not available new, so good used items must be sourced for that purpose.

Magnetism. As the operation of an EM pinball game relies on electrically generated magnetic fields, it should come as no surprise that ferrous metal components occasionally become magnetised. Relay armatures and coils, solenoid coil plungers and stops can all be affected. If they are, they will often not release when a coil is switched off. A relay will stay in the 'on' position, even when there is no longer power to the coil. Or it might be a flipper which stays in the up position. A good test is to simply touch the affected component with the game off. If it resets, there is a good chance it has become magnetised. If a piece of thin paper is placed between a coil core and relay armature, and it cures the fault, magnetised parts are very likely. The easiest way to overcome this problem is to change the magnetised parts for new or good used ones. It is not unusual for this to happen to the lock relay in a game, because it is always energised when a game is working. In Gottlieb games before the late sixties, the lock relay should de energise when the game is turned off and should not energise again until a coin is inserted or a replay is used. This action energises the relay which lights the game, amongst other things. If this relay becomes magnetised and stays in the energised position when the game is turned off, when it is turned back on, the game will light up. It will also have another effect. If the machine is turned off part way through playing a game, when turned back on, it will still be in that part played state. It really should start a fresh game if the relay is functioning correctly. Another common relay that can often become magnetised are the score relays in Bally bingo games. They operate frequently so often become magnetised over time. Sometimes, all five need replacing.

Coil sleeves, stops and plungers. Coil sleeves were originally made of non ferrous metal, usually Alluminium or Brass. Often these are worn paper thin or even through to the coil windings, by the constant action of a plunger sliding along them.  Modern sleeves are made from Nylon. It wears far less, and offers lower friction than the metal ones. Sometimes, the metal sleeves are very diffucult or impossible to extract from a coil. If this is the case, a replacement coil with Nylon sleeve must be fitted. If a worn metal sleeve can be removed, a modern Nylon one can be fitted to the existing coil. The plungers are often mushroomed at the end, and the stop they strike is often dished at the end, due to the constant action of one hitting the other. Stops are often spread and stuck in the coil sleeve. They do need to be replaced if they are worn. The mushroomed end of a plunger can be filed or ground back to a slight taper, and the end made flat again, if it is not too bad. A badly damaged one should be replaced. All coil sleeve / plunger assemblies should be rebuilt clean and dry. They should not be lubricated in any way. Coil stops are often loose in the bracket, even though they are held by a Nylock nut. Check them all to be sure they are all tight. Those used on the big reset bank coils are often loose.  Early Bally coil plungers are smaller than the sleeve they slide in, and have a split Nylon ring, which sits in a groove in the plunger, which does fit the coil sleeve. These are avilable new.

Pop bumpers. Faults can often be discovered when the bumper mechanisms have been dismantlled, even though they appeared to work OK before they were taken apart. The plastic bodies and bases can crack or break, especially the tits that protrude from the bases and locate in the bodies. The cap screw mounting holes are often broken because someone fitted screws that were too large for the job. The skirts wear around the thin edges. If the skirt has a pointer, it faces toward the top of the playfield, it is there to stop a ball sitting on the top of the skirt.  The rod ring assemblies are riveted together and the rods become loose on the rings. Coil sleeves become worn, plungers and stops also suffer from constantly hitting each other. The slot in the plunger wears. The Bakelite yokes wear where they sit in the plunger slot. The steel yokes suffer similar wear and often break in two. New reproduction steel yokes are as used in later games, with a curved edge, to stop them breaking. They are  stronger than the flat type used on early games. Willams games from the earlier years have a unique design of keyhole yokes which are no longer available. They can still be overhauled using a modified version, available as a kit. Spoon switches are usually full of solidified grease, which doesn't help the operation of the bumper. Clean this out of the spoon with a solvent and re grease it or leave it dry. Spoon and EOS switches need cleaning when a pop bumper is overhauled. Check the skirt spike is good and centred in the spoon. Fit new skirts if the old ones are faulty. Many games use the nuts & bolts that clamp the spoon and EOS  switch stack together as a conductor for one of the blades. If your stack has only three wires and four blades, it will work like this. It is worth removing and cleaning the clamping surfaces to ensure a good electrical path. I think it is a good idea to fit clear Mylar rings under the bumper bodies to protect the surrounding art work from damage. Every time a ring is pulled down, it forces the ball down and away from the bumper, putting pressure on the playfield. The Mylar rings protect the art from ball damage. There are two types available, adhesive and none adhesive. I prefer the non adhesive type myself. They are as originally fitted on the later EM games. They are highly reflective and do help to mask any imperfect touch ups around the bumpers, or where there is already slight wear. The self adhesive type are not original fitment, tend to be slightly opaque due to the adhesive, and just don't look as nice. There is an argument that the loose type trap particles of dirt under them, and that this can damage the art over time. I have removed hundreds of original ones, and have always found pristine art under them. As long as the play field is cleaned and polished regularly, I do not think this is a problem. The loose Mylar is easily lifted to allow polish to go under it and be buffed up. It is worth fitting new lamp holders when overhauling a pop bumper. It is an awkward job to solder them, so fitting new ones saves doing the job twice, when you find a refitted original is not working properly. Make sure the lamp wires do not touch the bumper brackets as they exit between the mounting lugs. Special insulation sleeve is available to ensure they cannot touch. Heat shrink tubing of the correct diameter, left unshrunk, will do the job fine.

Mounting screws. Any wood screws that will not tighten up properly should be attended to. Simply whittle a sliver of soft wood to the size of the screw hole, put a drop of superglue on the end and tap it in to the hole firmly. Leave it to dry for a few minutes and snap it off level with the surrounding timber. If it snaps off a little proud or uneven, tap it flat with a small hammer or flat ended punch. Then use a bradawl to make a new starter hole for the screw. Fit the screw and it will tighten up fine.