Flippers Locked On – Diagnosing Dead Coils and Transistors

So the next logical step after getting the driver board interface working in our Wizard Blocks build was to get the flippers flipping. Having a flipping whitewood is essential to making sure that the geometry of the playfield works.

We pulled the manual up for Star Wars Episode I (the game that we “upcycled” into Wizard Blocks… well parts-wise). The manual tells us exactly which wires in the wiring harness control which coils. Each flipper has its own dedicated power wire, so we ran those, and then ran the returns back to the molex connector at the back of the playfield.

We have a basic game software solution running that renders the blocks in place and controls the lamp and switch matrices. As a result, we get this:


However, as soon as the high power relay for the game is enabled (thus enabling power to the coils), the upper right flipper locks on.  In pinball, this usually means one or two problems: 1) A bad coil or diode on the coil or 2) a bad MOSFET on the driver board. Either way, something is shorting the coil power return back to ground causing the coil to get stuck on. This then blows the fuse on the driver board and deactivates the coil.

So time to dig out the driver board, the coil and the multimeter!

Bad Coils… Bad!

We easily removed the coil from the harness and I tested it with my multimeter. Generally you should get several ohms resistance between the common and power lugs, and 125-150 ohms of resistance between the left lug (common) and right lug (hold). The higher resistance is so the coil consumes less power when it is fully actuated (only enough voltage needed to hold the flipper up).



Alright, so as we can see, the specifications for the power and hold coils are all out of whack, so this coil is bad! Upon replacing the coil with a good coil (resistance checked FIRST this time…), the coil locked on and STILL blew a fuse. So it is likely that we have a bad MOSFET that the coil also destroyed. So now we have to chase the problem to the driver board.

Even Badder MOSFETs

Thankfully the driver board only mounts into the cabinet with two screws, so it is easily removed.

Pinball 2000 Driver board before cleaning

Pinball 2000 Driver Board (fuses removed)


When I tested the other FETs on this board, we should’ve gotten 1.2 to 1.4 reading on the multimeter, but the power MOSFET reads a mere 0.022, which is bad. So this will need to be replaced. The MOSFETS on this board are actually P20N10 transistors, however we will use a suitable replacement: the IRL540N.

Cleaning Pinball PCBs

Another thing that I noticed was that the board in the game was pretty disgusting. Even with the driver board cover, this board still managed to get a ton of dust from the cabinet and coils over time. I decided that this thing needed a bath. There have been extremely rare cases where I’ve seen humidity actually make a thick dust layer conductive, so this is a problem easily solved while we have the driver board out!

First, I put the board in the bath tub, removed the fuses and sprayed it with 91% isopropyl alcohol. I decided to use alcohol over water because the water here is pretty hard and will tend to leave a residue over time, so I didn’t want to risk it. The alcohol will evaporate quickly and clean any other gunk off the board. I also didn’t want to risk getting condensation buildup inside of the power relay housing.

I also used a small plastic scrubber brush to knock the dust layer loose and really work the alcohol in. Once the surface was clean, I also sprayed some Scrubbing Bubbles onto the board and gave it a few minutes to work itself in. I then scrubbed it a bit more with the nylon brush and then re sprayed it with the alcohol in order to displace any water that may have been in the Scrubbing Bubbles.

I then accelerated the drying process of the alcohol by hitting it with a small hair dryer on “warm” for a few minutes and then wiping it down with a towel.

The board looks much better!

Pinball 2000 Driver Board Cleaned

Pinball 2000 Driver Board Cleaned

Now to get things hooked back up and test out the flipper functionality!

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5 Responses

  1. mat says:

    awesome stuff! (i came here from pinside)

    • Jimmy Lipham says:

      Awesome! Glad to have you here 🙂

      Pinside is a great resource, and they’ve been instrumental in helping me diagnose issues over the years. They have also really been great at suggesting new features for Wizard Blocks!

  2. mat says:

    i cant wait to see more! As a matter of fact, youve inspired me to go on the hunt for another RFM. Im glad to see pin2000 get some love, and reallly want to see the finished product. Looking forward to your next post. I hope one day you could sell that control board, it would be awesome to write my own game code!

    • Jimmy Lipham says:

      As soon as I get the bugs worked out on my end, I’d be more than happy to try to hook you up with one (just cover parts and shipping). The game code is in Unity3D/C#, so its not hard to learn and there’s a ton of documentation in the community on C#. Its been quite fun! 🙂

  3. Mat says:

    OMG, that would be awesome! I hope to have a RFM pretty soon (its tax return time!, gotta spend it before the wife does). Hopefully in the next two weeks. Let me know about that board. I would love to be able to try some ideas ive been stewing on for the past few months. TIred of waiting for NUCORE to come back to life, gonna take matters into my own hands! Anyways, how are things progressing? Im going into withdrawls here! I need an update!