An intermittent function on a Bally EM that comes and goes when the plug is moved.

Bally connectors: fatigued female pins

Cause: Bally made its own connectors; the female contacts fatigue and lose tension or break. The male half is fine.

Checks

• Check the female contacts for broken or slack fingers.

Fix

• Do not unplug and reseat Bally connectors to cure faults; every cycle weakens them further.
• Replace a bad female half with one from a Gottlieb or Williams parts game, since new ones are not made.

Systems

• Electro-mechanical

Related tips

• Clean EM pin connectors
• Wires broken off switch solder lugs (1970s EMs)
• Old bakelite plugs crack easily

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