Auto Eddy Board

In Cirqus Voltaire, Williams introduced a new eddy board. Earlier eddy boards were difficult to adjust. They were either insufficiently sensitive to read a ball, or they locked up during play. The auto eddy board uses a microcontroller and digital potentiometer to precisely adjust the set point for maximum sensitivity. The problem is, that the set point may be unstable and cause lockups. Therefore, Williams added a control line to allow the machine to reset the board, should it lock up. Unfortunately, the reset happens only after the ball drains, which is no fun for the player. Williams also added a delay capacitor to reduce lockups, but that slows the senor down. It misses about 30% of ringmaster hits.

Therefore, removing C3 can help with a sluggish game, but may cause lockup problems. There is an aftermarket microcontroller, developed by Pinbits, that continuosly recalibrates the board, and resets whenever necessary. With this microcontroller and C3 removed, the system becomes significantly more reliable.

A Monster Bash auto eddy board with C3 removed

There are two variants of the board. One works with high-frequency sensors, typically flat coils made from a four-layer PCB. The other works with low-frequency sensors, which look like green resistors and fit into slots under the playfield. These sensors are used onm Star Trek: The Next Generation and Monster Bash inlanes.

The Diagnostics LED

When the board powers up, it goes through the following sequence:

Fast flashing: rough calibration of the sensor
Faster flashing: fine calibration of the sensor
LED off: ready to read
LED on: ball detected

What Goes Wrong

The most common problem is unreliable operation. The upgraded eddy controller solves this problem, improving hit detection for the Ringmaster and improving reliability of the Monster Bash Phantom Flip. Another cause of unreliable operation is weak connectors, losing spring force and becoming sensitive to vibration.

The next problem is broken transistor legs. The vibration in the machine causes the transistor legs to crack - but the may still look good. The transistors need to removed, the legs shortened, and replaced back in the board. This problem is indicated by a working LED, but no switch signals in test mode.

Finally, like anything connected to the switch matrix, the output transistors can be destroyed by a voltage short.