The flasher supply filter capacitor bursts; flashers may glow dimly when the flippers are used.

+20 V filter capacitor C11 (C10 on WPC-95) blows apart

Cause: Coil voltage feeding back into the 20 V flasher circuit: a shorted flipper coil diode or a shorted Fliptronics transistor, a backbox ribbon cable fitted one row off its header, or J124 plugged into J128 (they share the same keying).

Checks

• Check every ribbon cable is seated on the correct header rows.
• Check J124 and J128 are in their own sockets.
• Operate the flippers: a flasher lighting faintly suggests a bad Fliptronics transistor.

Fix

• Fix the cause and replace the capacitor.
• Preventive fix: on a WPC-S or earlier board lift the lower leg of the 10 W ceramic resistor R224 (the leg just above TP7; R9 on WPC-95), solder the non-banded end of a new 1N4004 (or 1N4007) to that leg and the banded end into the vacated hole.

Systems

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

Related tips

• Getaway: beacon runs nonstop in test and driver board C11 overheats
• Why WPC coil diodes are on the driver board
• "Check Fuse F114/F115" (F106/F101 on WPC-95): step-by-step
• Testing a coil diode on the driver board
• Testing lamp-row drivers with a test lamp
• Testing lamp-column drivers with a test lamp
• Fliptronics flipper coil wired wrongly
• Testing the diodes on a flipper coil

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