Stepper cleaning, part 2: free a seized shaft

Steps

• Spin the cog by hand (clockwise seen from the cog side; hold a coil in if needed). If it spins freely, skip to cleaning the rivets.
• On two-coil units, release the clock spring and count the turns as it unwinds (usually three or four); write the count on the unit.
• Pull the shaft and cog out from the cog side, swinging a switch stack aside by removing its screw nearest the contacts if it is in the way.
• Clean the shaft with alcohol and smooth it with 400-600 grit or a green pad (no steel wool). Photograph any springs you remove.
• Clean the shaft bore with alcohol on a cotton swab.
• Put a thin film of Teflon gel on the shaft, refit it and any moved switch stack, and check the cog now spins freely.
• Rewind the clock spring by the counted turns and refit other springs.

Systems

• Electro-mechanical

Related tips

• Stepper cleaning, part 4: refit and test
• Cleaning and aligning an EM stepper unit
• What stepper units do in an EM
• Kinds of stepper unit
• Setting an EM game to free play
• Faults that point to a stepper unit
• Ball release coil stays on: burnt wires behind a stepper plate
• Set stepper wiper finger tension and alignment

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)