The Art of Pinball Machine Maintenance

Keep your playfield clean

Any dust between the ball and the playfield will act as a grinding agent damaging the finish of the playfield of your pinball machine. Apart from common or garden variety dust, all moving parts give off a fine metal dust as they wear.

A slightly damp cloth must be used to keep the playfield of your pinball machine dust free. I use the Novus polish range on my playfields to clean and maintain the finish. Plastic polishes for the automotive industry work well on pinball machines that have a "Diamond Plate" or similar coating on their playfields. These coatings are mostly urethane or polyurethane based which essentially makes them plastics.

On older pinball machines you have to be very careful, I mean "extremely bloody cautious" about what you can use to maintain and protect the playfield. Most of those paints or inks will weaken and separate from the plywood substrate when they are exposed to moisture or solvents. Do your homework and test everything first. For the best advice refer to Shaggy and Norm.

Keep the cabinet and back box dust free

On old electromechanical pinball machines there are two things out to kill your machine. Wear and dust. Dust can cause switch contacts to isolate or short (in the case of metallic particles) when they shouldn't. A worn out switch will make the relay logic fail and cause your machine to act up. The more dust you have, the faster things will wear out.

Contact Cleaner

Do not use contact cleaner. High voltage switches will spark, creating heat and causing the contact cleaner to crystallise. You'll soon see a white residue on your switch contacts that doesn't conduct electricity.


If there's one thing worse than dust, it's dust collecting on a film of oil. One of the first things I do to revive a machine is to strip the flipper assemblies to remove the grime in the coil sleeve. This goop is caused by a light spray of WD40, Q20 or similar product. If your flippers are sluggish its probably a dirty EOS switch so clean that first. The coil sleeves are made of nylon which has a very low coefficient of friction with the steel of the plunger. They're designed to run dry.

Replace your balls

Anywhere you have metal on metal contact like the thumper rings, saucers, ramp flaps, chutes and ball guides you'll be scratching and denting your balls. A dull ball should be replaced. The normal size ball has a diameter of 1-1/16" (26.9875mm).

New ball. Will glide over your playfield without causing wear.

Middle aged ball. some scratches start appearing. The tiny burrs associated with each scratch will initially scrape off a tiny bit of the playfield untill the burr breaks off. Will cause wear continuously when scratches are deep and sharp.

Old, spent-two-years-in-damp-storage ball. This atrocity must be discarded immediately. You may as well be sanding your playfield with 80 grit paper.


Replace your rubber

Rubber rings have to be replaced as soon as they start showing cracks when they're stretched. They start to crumble and those crumbs will cause havoc. If they're still young and soft your ball will bounce over them causing impact damage. If they're old and hard they will cause scratches. A death of a thousand cuts can come quickly to the unwary.

Unprotected posts will not only mark your balls but the post itself will start to bend. It's actually ripping itself from the playfield, not bending, meaning your pinball machine is taking major, hard to fix damage.

Also think about replacing the mylar when it cracks or ripples for the same reasons.

Replace the batteries

Solid state pinball machines have batteries to remember settings, logs and high scores. Replace the batteries in the back box to stop them from leaking acid onto your expensive and hard to find boards.

If at all possible, make yourself an external, plug in battery holder with a "one way only" connector like you get for connecting battery packs for radio controlled stuff.


Your pinball machine is crammed with little heaters called bulbs who all conspire to dry out your rubber, warp your plastic and attract dust. They create even more heat when they are dusty. (Less infra red energy to escape through the playfield glass, among other reasons).

Do not remove your tilt mechanism

A pinball machine is designed to be shaken. It's part of the game. The tilt mechanism is there to stop you and yours from breaking the legs off, ruining your floor or blatantly cheating. Adjust for maximum satisfaction.

Play your machine

Give your pinball machine a "birthday" and make a point of changing the batteries and inviting some friends over to celebrate another year of free pinball. Electro-mechanicals benefit from playing due to the wiping action designed into the switches to keep them clean.

Where to buy spares and machines

Here's a link to Marco Specialties where I've sourced everything I've needed so far. They also sell brand new Sterns. New machines sell for around (US)$5000 and shipping to South Africa is (after checking with Marco) around $750.00. Also give The Pinball Resoure a look for all things Gottlieb.













When Silicon goes bad

Solid state machines run on diodes, integrated circuits (IC's) and transistors. The main failures on a board can usually be ascribed to a transistor failing. Finding the failed part can be a pain when they don't physically blow up or burn. Here is my attempt to make the finding of these failed units a bit easier by giving you the idiots guide to how a diode and a transistor is made. Bridge rectifiers are also made up of diodes. All the tests below rely on a multimeter with a diode test function.


A diode is a two wire device that has a piece of Silicon (Si) at its core. The Si is doped on one side with atoms that have more electrons than Si resulting in n-type Si and on the other side with atoms that have fewer electrons than Si resulting in p-type Si. The n-side with the surplus electrons is called the cathode and the p-side is called the anode. In a normal diode and under normal operating conditions, current can only flow through it from the anode (A) to the cathode (K).

In the figure below is the schematic symbol for a diode and a representation of a typical diode. The stripe indicates the cathode.

To test a diode you need a multimeter with a diode test function. In this mode the multimeter will generate a voltage between the two leads making the red lead more positive than the black one. When you connect the red lead to the anode and the black lead to the cathode, your multimeter will show you the voltage drop over the diode. This is typically around 0.6 Volt for a good diode. When diodes fail they can create an open circuit (no change in the readout) or a short (0V).

In most cases diodes can be checked without removing them from the printed circuit board (PCB) or the coil.


A transistor consists of three layers of Si. You get pnp transistors that have a piece of n-type Si between two pieces of p-type Si and you get npn transistors that have a piece of p-type Si in a n-type sandwich. The two outer layers are called the collector and the emitter. The middle piece is called the base.

In the pinball world transistors are used as switches. An npn transistor will allow current to flow through it from the collector to the emitter as soon as the base voltage goes far enough above the emitter voltage. A pnp transistor will let current through it from the emitter to the collector as soon as you drop the base voltage far enough below the emitter voltage.

The figure below shows the schematic symbols for pnp and npn diodes as well as the equivalent diode representations for testing purposes.

When testing transistors you can regard them as two diodes back to back. For npn transistors connect the multimeters red probe to the base and check the voltage drops with the black probe on the emitter and collector. Base-emitter voltages are typically 0.6V but base-collector voltages can vary. Driver boards usually have 4 or 8 of the same transistors. A bad transistor will be the odd one out.

For pnp transistors the black lead should be on the base and the red lead used to test the collector and emitter. As with diodes, transistors can be tested in circuit in most cases.

The figure below shows the pinouts for commonly used transistors. Data sheets for transistors can easily be found using Google.

Bridge Rectifier

A bridge rectifier is a four terminal device made up of four diodes so that when alternating current is applied to two of the terminals, direct current is produced between the other two. Well, sort of.

The figure below shows the schematic symbol for a bridge rectifier. When AC (alternating current/voltage) is connected to the terminals marked with a ~,  the waveform (usally sine wave coming from a power transformer) is rectified so that current will flow out of the terminal marked with a + and into the terminal marked with a -.

A capacitor is usually added between the + an - terminals to smooth the resulting voltage. Testing a rectifier is accomplished by connecting the black lead to the + terminal and the red lead to the ~ terminals. You should see one diode drop (voltage drop of one diode) of about 0.6V

Checking the other two diodes is done by connecting the red lead to the - terminal and the black lead to the ~ terminals.This is somewhat counter intuitive but you can see from the figure above that this will give you the right result.


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