One or both flippers lack power.

Weak flipper: worn mechanism

Cause: Wear in the flipper mechanism, classically a mushroomed plunger dragging in the coil sleeve, or a shaft binding in its playfield bushing.

Checks

• Lift the flipper bat from above: it should have about 1/32" to 1/16" vertical play.

Fix

• Rebuild the flipper.
• Reset the vertical play by adjusting the pawl's clamp on the shaft from under the playfield.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Solid state flipper very weak: power side has failed
• Both flippers equally weak: check the flipper supply bridge
• Flipper stuck up with power off: binding or worn pawl
• Last Action Hero flippers go weak during multiball: replacement flipper board
• Solid state flipper does not work: fuses and fuse clips
• Flipper stuck up with power on (Playboy and later)
• Solid state flipper has no power though fuses are good
• Solid state flippers dead, weak or intermittent: clean the switches

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)