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This post is intended to show the basic components of the Atari trak balls for Centipede and Millipede and what to replace to get one to roll like new again. The Atari Mini-TrakBall (Centipede) and Midi-TrakBall (Millipede) consist of 2 roller shafts, 1 idler shaft, 6 ball-bearings, 2 radial optical couplers, 2 encoding wheels, and a ball. The basic setup is shown below. Key: E - Encoder wheel is screwed on to end of shaft. B - Ball-bearing D - Detector Diode The trak-ball rests in the middle of the assembly and theoretically has 3 tangent points of contact in the middle of each shaft. As the ball is rolled the shafts turn the encoder wheels at the appropriate rate which is detected by the logic card and fed back as motion on the screen. .__ | D __E__ | | `-- | B | . B . | . | . | . | Trak-Ball . | B | | | B | B------------------B-----E | | | |__D__| When the cover is taken off the trak-ball assembly the 3 shafts are always grooved in the center of the shaft. .----------.......-----------. -- -- `----------^^^^^^^-----------' At first it may look like it's designed this way so that the ball rests in the groove. This is actually wear and tear. The plastic ball wears down the metal shafts over time which binds the ball. All shafts should be perfect cylinders as shown below. This way the friction between the shaft and the ball is optimum. .----------------------------. -- -- Idler shaft `----------------------------' .----------------------------. -- ---------- Roller shaft `----------------------------' The roller bearing can also get gummed up or rusted. There always seems to be an array of dirt and coke spilled into the trak-ball. If the bearings seem to roll pretty good without binding I don't recommend replacing them. The biggest improvement though comes from replacing the shafts. The Centipede Mini-Trak Ball is 2 1/4 inch diameter and the Millipede Midi-Trak Ball is 3 inches in diameter. The roller and idler shafts also have a larger diameter in the Midi-Trak Ball. If you have a Centipede or Millipede and plan on keeping the game, I recommend buying a new roller set and bearings. The play improves dramatically. PARTS: The best prices I have found on bearings and shafts are at ANSCOT Distributing Co. 1-800-456-7277. Please post if better prices are known. Roller Sets: Millipede $9.95, Centipede $6.95. Bearings: $2.99 each. The bearing price just kills me but WICO wants $5.00 each.