Holding the button makes the flipper chatter up and down instead of staying up.

Flipper flutters when held (Time Machine and earlier)

Cause: The thin hold winding has broken, usually where it leaves a solder lug; the middle lug should carry both the thick and thin wire.

Checks

• Look for a loose thin wire at the lugs.
• Measure the coil before changing any transistor.

Fix

• Resolder the winding or replace the coil.

Systems

• Data East CPU Version 1/2

Games

• Laser War
• Secret Service
• Time Machine
• Torpedo Alley

Related tips

• Weak flipper on Time Machine and earlier: pitted switch contacts
• Flipper coil runs very hot (Time Machine and earlier)
• Flipper circuit on Laser War to Time Machine
• Checking a pre-solid-state flipper coil
• Flipper only has hold strength after a rebuild: EOS wire on the wrong coil lug
• Pre-solid-state flipper keeps blowing its fuse
• Flipper sometimes sticks up, even with power off: replace the coil sleeve
• Solid state flipper flutters when held

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