How to Test a Pinball Coil with a Multimeter

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Have you heard of a pinball coil? In case you didn’t yet, a pinball coil is a roll of magnet wire wrapped around a cardboard or plastic spool or bobbin. It’s the key component in a device known as a solenoid. 

A solenoid is an electromechanical device composed of the coil, a plunger or armature inserted into the coil’s center, and some actuators or links attached to the plunger that move when power is applied to the coil. 

A relay is a kind of solenoid that runs switches. Electromechanical pinball machines might have more than 100 solenoids and relays. On the other hand, newer solid-state games typically have a dozen or more than that. Arcade or pinball game coils come in many different sizes and shapes that differ based on the type of application. Further, they vary by several turns of wire on the spool, wire thickness, and spool size. 

More about Pinball Coils

You will find many reasons as to why pinball coils malfunction. You need to understand that some coils are replaced unnecessarily. Below are some crucial points you need to remember every time you are troubleshooting a solenoid coil issue.

  • Failed coil diodes cause many coil malfunctions

The coils might have a diode connected to the terminals in solid-state electronic games, particularly older machines. The diose on the coil functions a very important function as a one-way electrical wave. 

Once used along with a coil, they act as a pressure relief valve. Once the coil is turned off, the residential magnetic field from the coil also collapses and causes what professional electric engineers call back electromotive force or back EMF. 

Ideally, that’s a very short but big reverse voltage increase, which leads to the magnetic field’s inertia. That increase might be hundreds of volts. Just imagine the water hammer which results once you turn off a valve immediately on a poorly made plumbing system. 

That back EMF increase could shoot back to the driver transistor. Eventually, it will damage it over time, causing transistor failure. The diode on the coil functions like a 1-way valve, networking that energy back into the coil and dispersing it as a small harmless piece of heat. 

Take note that coil diodes could fall in two different methods:

  1. wrong installation or
  2. through eventual vibration, temperature, and heart failure over time 

Whenever you change a coil, you need to pay attention to the diode’s direction before you start removing the coil. Are you still unsure of the direction of the diode? 

Then it will help if you check the game’s service manual or schematics to identify the proper diode direction. 

  • Coils don’t need any lubrication

TAKE NOTE: do not ever lubrication your coils. Lubricating coils is undoubtedly a surefire way to wear them out and ruin them. Remember that the nylon sleeves utilized in nearly all coils function as a plunger’s natural lubricant. All it requires is a careful cleaning and replacement of worn parts. 

Other spray lubricants also produce a fire hazard. That’s because their fumes are extremely flammable. There are also some instances of coin doors being blown off of games. So, always watch out.

  • Coils either work, or they actually don’t

In most cases, a flipper rebuild kit is an answer for those weak coils, particularly flipper coils. Bear in mind that worn components often result in dragging and tarnished solenoid performance.

Moreover, bad switch contacts obstruct power flowing to the coil. Coil sleeves become damaged, putting a drag on the links and plunger. 

Are you currently fixing your game on a tight budget? You can always try changing the coil sleeves and see if it will fix the problem. They are affordable and will put more zip into the flip. 

Another cause of weak coils, particularly on flippers, is a damaging end-of-stroke switch that switches the coil from a high-power flip mode to a power-saving mode. It lowers energy use and stops the coil from overheating.

Can You Test Your Pinball Coil with a Multimeter?

Yes, you can! In fact, using a digital multimeter on your pinball coil is the fastest and most reliable way to test the coil. 

A multimeter is a tool you use when repairing electronic pinball games. It’s utilized more than any other pinball repair. Did you know that digital multimeter does many good things such as:

  • measure capacitance
  • test transistors
  • test diodes
  • measure resistors
  • measure voltage
  • test for continuity

An electronic pinball game repair must not even be initiated without a reliable digital multimeter. It is perhaps the single most valuable tool you can use. 

So, here’s how you can test your pinball coil with a multimeter.

  1. Grab your digital multimeter and set it to ohms resistance. What you will do is measure the resistance across the coils. What you are supposed to get is a reading of at least two to three ohms. Anything higher than that will indicate that your coil is okay. 
  1. Now, put your meter two resistance and insert a lead on each of the coils. Remember that it does not matter because you will go in either direction.
  1. Check the readings. Do you get three ohms or higher? Then your coil is fine. 
  1. You also like to run through the entire machine. Check all the leads and ensure that the resistance is correct. If you run into one you assume is shorted, you can move it, possibly cutting the leads off of it and check it without being wired into the machine. 

Often, some of those have diodes running across them, and it could be a diode causing some issues. Hence, you would like to go through them all and check to guarantee that all coils are good. That is the next step in your survey of the machine before applying power to it. 

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