Williams relay hum from a missing armature rivet

Williams relays have a brass rivet on the armature plate. If it is missing, or occasionally loose, the relay can hum. Far more often the hum is just a relay adjusted too tight.

Systems

• Electro-mechanical

Related tips

• EM relay buzzes or hums loudly
• A hold relay hums or buzzes
• Gottlieb relay return springs
• How latch-trip (interlock) relays work
• Relay banks and their reset coil
• Relay coil resistance and frame sizes
• Gottlieb AS relay (miniature match stepper)
• Push relays in by hand gently and straight

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