A flipper coil runs hot during a session though the button is not held.

Fliptronics: flipper coil gets hot after a while of play

Cause: A dirty U-shaped opto on the cabinet flipper board makes the button flicker on and off; or a failing LM339 at U4/U6 on the Fliptronics board (U25/U26 on the CPU board of a WPC-95 game). Rarely, poor 12 V regulation from the driver board 7812 or its filter capacitor.

Checks

• Swap the two flipper opto boards: if the fault moves, it is the opto.

Fix

• Clean the optos; replace the opto or the LM339.

Systems

• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Fliptronics and WPC-95: weak flipper
• Two LM339s on the Fliptronics board read the flipper optos
• Flipper gets weaker the longer the game is on
• Weak or dead flippers from failing LM339s on the Fliptronics board
• Optos test good but still don't work: the opto board
• A dedicated (direct) switch does not work
• Resets remain after rectifiers, caps and connectors are done
• "Check Fuse F114/F115" (F106/F101 on WPC-95): step-by-step

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