The flipper stays energized up.

Flipper stuck up but drops when the power goes off

Cause: Pre-Fliptronics: a cabinet flipper switch stuck closed. Fliptronics: a poorly seated CPU-to-Fliptronics ribbon, a bad or dirty cabinet opto, or a mechanical cabinet switch on pre-opto games.

Checks

• Check the cabinet switch or opto board.
• Reseat the ribbon cables between CPU and Fliptronics boards, fitted correctly.

Fix

• Adjust or replace the switch; clean or replace the opto.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Fliptronics: flipper will not hold up (flutters)
• Right flippers energized at power-up: replace the ribbon cables
• How Fliptronics flippers work
• Checking flipper buttons and EOS switches in switch test
• Fliptronics and WPC-95: weak flipper
• Flipper stays up briefly after the button is released
• Upper flipper switch reported bad on a game with no upper flipper
• Flippers and magnet weak after rebuilds: replace the Fliptronics board

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Two, Clay Harrell (pinrepair.com)