Outerworld Arcade
Space Encounters

Midway Space Encounters / Omega Race / Sea Wolf II
Angle Encoder Rejuvenation

Angle EncoderAngle Encoder

Midway utilized two angle encoders (part number A080-91110A0) for player input in Space Encounters. Some units of Omega Race also utilized these encoders. After years of use (or disuse) these encoders can start to get jittery, making game play difficult or impossible. These units were unfortunately not made to be serviced easily and in fact seem to have been made in order to not be serviced. They do not utilize a potentiometer, which can be lubricated when they start to get jittery. I recently opened up one of these units to try to see what was in them and if it could be repaired.

Here's the unit revealed:

Angle Encoder Revealed

The core of this unit is the encoder wheel, a plastic disc with a metal overlay pattern, which sends signals to the CPU telling it the angle the wheel is at. Eight metal sensors conduct as they touch the metal pattern in the disc. (Click each image blow for a larger version.)

Encoder WheelEncoder Sensors

There are actually sixteen metal sensors in the unit, but, as you can see in the picture below, the sensor only has the metal overlay on one side. It does have grooves on both sides. These grooves and the additional sensors could simply help keep the wheel aligned.

Encoder Wheel Back

As you can see in the picture, the metal on the encoder wheel had become dirty and dull with time, causing poor conduction and jittery movement. After washing it down with some 409 and a pencil eraser the wheel again shined like new.

Here's what the encoder wheel looked like before and after cleaning: (click image for larger version)

Angle Encoder - BeforeAngle Encoder - After

After taking this one apart brute force, here's how I'd approach repairing the next one:
1. Remove the pcb board from the rest of the unit by desoldering the pins from the board.
2. Cut the plastic sides and remove the metal side pieces.
3. Drill out the plastic connectors holding the encoder layers together.
4. Remove and clean the Encoder wheel and the metal sensors that contact the wheel.
5. Reassemble the layers and bolt them together.
6. Resolder and possibly add a socket reconnecting the pcb board to the rest of the unit.

Here's a final picture of the entire unit expanded with the parts in order:

Angle Encoder Expanded