Pressing the flippers gives points even when the ball is nowhere near a target.

Using the flippers scores points: a target switch closed by vibration

Cause: A loose target switch was being closed by the vibration of the flippers.

Checks

• In switch test, press the flippers and note which switch shows on the display.
• Rap the playfield by hand in switch test to find over-sensitive switches; targets often get pushed closer each time they are hit.

Fix

• Tighten and re-gap the offending target switch.

Systems

• Gottlieb System 3

Games

• Street Fighter II

Related tips

• One switch row works in test but not in play: overheated strobe MOSFET Q36
• Pressing a flipper also triggers the opto switches: bad diode and botched ground repair

Source: Pinball Repair help group!! (Facebook group)