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Twilight Zone Trough Eddy Set


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This set replaces the TZ trough sensor (A-16533), prox board (A-16534) and cable (H-16618). This improved design is compatible with the Williams original boards, and all parts are fully interchangeable. Simple adjustments make it easy to get the system running right, and staying right.

The sensor board has an adjustment pot that takes care of machine-to-machine variations.

The twisted cable reduces losses in the wiring, maximizing the sensitivity at the coil.

The bracket has slightly longer slots, increasing the flexibility of installation.

With the parts installed in the machine, and  the sensor board loosely set well clear of the trough, rotate the pot clockwise until the LED comes on. Then, back it off a tiny fraction until the LED goes off. This setting is where the sensor is most sensitive (see note on hysteresis below). Now, slide the coil towards the ball in the trough until it just touches the ball, then move it back about 1/8". At this point, the LED should be ON; if it goes off, you will need to be a little closer to the ball.  Snug the screws down and make sure that the coil sensor points directly at the closest point of the ball - you can rotate, it, and slide in two directions, to do this. Make sure that the sensor reliably detects a steel ball by pushing the ball away from the sensor with your finger, from the top of the playfield. Make sure that the sensor registers again when the ball rolls back into position. If not, slide the sensor a fraction closer.

When the ball rolls into the trough, it will bounce a tiny, tiny fraction of an inch forwards at the end of its travel. If the coil is in contact with the ball at rest, it will get pounded by the ball and shatter. So make sure that you have a small gap between the ball and the coil.

If the pot is set too close to the sensor point, the chip has a feature called hysteresis that might cause trouble. Hysteresis means that the sensor has to go back past the trigger point to change state, so that it doesn't flutter. If the pot is too close, the sensor may not detect the ball after the first read. If this seems to be a problem, back the pot off a fraction more.


  • Model: TZ-PROXSET
  • Shipping Weight: 0.25lbs
  • Manufactured by: Pinbits

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