Coil & Lamp Problems

Coil & Lamp Problems

IMPORTANT: Please read the following before attempting to check your machine.

The following advice is intended for people with some experience of handling the voltages mentioned.

As a general rule, playfield voltages can vary between 6 and approx. 80 volts and can be even higher where neon tubes are in use. Do not attempt to undertake these checks if you are in any doubt about your ability to carry them out safely

Bear in mind that previous repairers may not have carried out repairs correctly or safely.

Some older games have much higher voltages under the playfield and in the cabinet. If in doubt, do not attempt the repair yourself.

The Pinball Heaven accepts no liability for damage or personal injury caused as a result of performing the following, or any other tests or repairs suggested in these pages.

Faulty coils are one of the main reasons for a pinball machine breaking down. In this guide we intend to help you troubleshoot the problem, quickly and easily. Because coils and flashlamps are virtually the same, you can use the same diagnostics to repair them.

This guide is intended for the WPC (Williams/Bally games 1990+) system, but can easily be adapted to other systems.

The most common reason why people phone us to ask for technical help on coil problems is because newer games (late 1993+), use a switch on the coin door to disable coil/flashlamp power when the door is open. Operators frequently forget this and don’t shut the door before testing the machine!!

Where to start…..

If you suspect that a solenoid is not working properly (or not at all) put the machine into Test Menu, T.4 (or T.5 for flashlamps) and select (using + / – keys) the suspect coil (or lamp) and on newer games – close the door!

The coil should pulse repeatedly, quicker at first, then more slowly. If not, press the start button for help; the display will indicate which wire colours are used, which connectors on the board control the coil and which fuse to check. Start by checking the fuse!

If the fuse is OK, then get your digital multimeter out! Lift the playfield up and locate suspect coil. The coil will have two lugs on it with wires connected to it (3 lugs on flipper/continuous duty coils), make sure the wires are attached.

Now, with your meter, put the black (negative) lead to earth (you can usually wedge the probe of the lead under the metal brading which goes all around the inside cabinet. Put the red lead, in turn, to both sides of the coil and note the results.

There is usually around +78VDC on the solenoid circuit and +24VDC on the flashlamp circuit. You should get approximately (under 1 volt) the same voltage on both sides of the coil (or bulb).

No voltage indicates a power problem. Follow wires back to board, (due to the way these circuits are wired up, a wire could have fallen off another solenoid, which could still be working but could be the root of your problems), if you only have voltage only on one side of the coil, the coil is most probably defective, replace it.

If you have power to both sides of the coil, then the problem is most likely in what controls the device. Press start again and note the transistor numbers (prefixed with Q), there could be two or three numbers, one is the pre-drive (little transistor), followed by the main drive transistor(s). High current coils (typically 23-800 coils) use the three transistor system, others, including flashlamp just use two. The predrive is a 2n5401 transistor, the main drives are TIP102 and (if used) TIP36C for high currents

Get a piece of sheathed wire (appx 3′ in length) or put your meter onto DC current test, 10Amp setting (your meter will now act like a piece of wire). Put one end of the wire to the earth, the other; momentarily touch to the metal tab on either TIP102 or TIP36C, the coil should then ‘pull in’ (energize). If it does, then the fault lies on the board, you should either send to us for repair or ‘phone for advice. If it doesn’t, then the fault lies between the return wire (usually the thinner wire on the solenoid) which can be identified by looking in the front page of the manual.


Check the wire carefully for damage.

Good luck!

Leave a Reply