Eddy Sensor Board Fix – A-18543-1

The Eddy sensor board found in a few games from Bally Williams including Roadshow, Scared Stiff and Theatre of Magic. The design allowed a ball sensor to mimic a switch, but without the need for it to protrude into the playfield. Over time though, a couple of the components can go bad – causing the switch to begin to work intermittently – or ultimately fail. There are some great after market options of ‘self calibrating’ Eddy boards, with another option of a self calibrating Eddy board here. If however you don’t want to go with an aftermarket board – I would suggest trying this Eddy Sensor Board fix first and see how you get on.

What is an Eddy Sensor Board?

The Eddy Sensor Board is a small board that controls a sensor to let the game know when the ball has run near it, instead of using a conventional switch to control this. The board has a power on board on a three pin connector to the left and a two pin connector to the right which controls the actual sensor itself. The sensor very rarely goes bad – but there are two common components to try and replace or work with. If you take the board out, you may as well do both of these fixes to eliminate any potential issues. Or fix one issue only to find out you need to complete the other Eddy Sensor Board fix a few months later. Whilst not usually a hard board to pull, it is just good practice.

Before pulling the board

Before pulling the board at all, the first thing you are going to want to try is adjusting the potentiometer. Yeah, that’s what I said. Potentiometer. Essentially it is a variable resistor that adjusts the sensitivity of the sensor. If this is out of whack, the game either doesn’t read the ball travelling over the sensor, or thinks it is there all of the time. So with the board in the game, and the game switched on (coin door open I would suggest please) adjust the potentiometer with a small screwdriver by turning the adjuster anti clockwise, do this until the LED to the left of it comes on.

Eddy Sensor Board Fix - Adjusting the potentiometer
Adjust the potentiometer to anti clockwise until the LED comes on

Once the LED comes on, you will want to very gently and slowly turn the potentiometer adjustment back clockwise until the LED just turns off. If you think you have given it too much, just restart the process. Like any switch you want it to be really responsive in the game.

Adjust the potentiometer again to the right until the LED JUST turns out

Some people have had success in then adding a bit of clear nail varnish into the potentiometer to “lock in” the adjustment. You can try that, for me, if the potentiometer is going out of adjustment that often, that fix feels a little poor. I would just follow on this guide and swap it out with a modern, higher quality replacement item.

First Point of Repair

If you have tried the above adjustment and that isn’t giving you the traction you hoped for. The first point of repair is the two pins that link up to the sensor itself. The pins can become dirty, tarnished and the solder to the board, due to vibration can become weak and fail. Stage one of the Eddy Sensor Board fix is to pull the board, clean it and check the solder. As you can see below, the board out of my Scared Stiff didn’t look too bad.

Eddy Sensor Board

Still I cleaned the board, with the pins in-situ gave them a good clean with Isopropyl alchohol and where it wouldn’t clean up just run some fine grit sandpaper over the pins. They really weren’t in poor shape. I did also just reflow the solder too, following up with one more run of isopropyl.

Replacing the Potentiometer

The potentiometer used in this game 10kΩ 0.25W. Where the manufacturer item falls down is that it is a single turn potentiometer meaning that the range of adjustment through the variable resistance is quite low. So the level of adjustment that can be dialled in, is low too. Given that the game over years and years will have taken a serious bashing. On top of the fact that this item has a moving part. It is no surprise it is prone to failure. The replacement part I found is a 12 turn item, giving much greater opportunity to adjust within the same tolerance. The item in question is a Bourns 3266 – 1/4 ” Square Trimpot® Trimming Potentiometer. You can find this in the UK from RS components for just £3.72 inclusive of VAT.

New Potentiometer for Eddy Sensor Board Fix

Once arrived you will notice that the third pin at the top of the potentiometer requires some adjustment to complete the Eddy Sensor Board fix. So before I installed the item, I made a 10mm jumper wire. Tin one side of the wire and solder it to the third pin. I then desoldered the old potentiometer and discarded that to the bin.

Desoldered old potentiometer in preparation for Eddy Sensor Board fix

I then started to adjust up the jumper wire with the other two pins in place. As you have a good solder on the third pin, you should be able to seat the potentiometer solidly and adjust the jumper wire as required to get a good, solid fit. Once done, simply solder all in place and put the board back in the game.

Final Calibration

Like before you will need to complete the final calibration by turning the potentiometer anti clockwise and then clockwise once more to get the LED to go out. However, you can see this fix, whilst not using original components is a great upgrade to the board. I have played around 20 games now on my Scared Stiff and where the Eddy Sensor Board would usually flake out, since this fix, the game hasn’t skipped a beat.

You can find more repairs in my pinball repair blog and if you would like someone to take a look at your board, and complete an Eddy Sensor Board fix using this method, please check out my UK Pinball Repair section. If you aren’t local to me, I can put you in touch with someone who will be able to help. Thanks for stopping by, don’t forget if you have something to add, please comment in the comments section below.

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