A single flasher stays dark.

One flasher never lights

Cause: The bulb, its TIP102 driver, broken socket wires, or the pre-driver transistor.

Checks

• Swap the bulb.
• Check the socket wires.
• Check the driver and pre-driver transistors.

Fix

• Replace the bulb, wiring or transistors.

Systems

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

Related tips

• No flashers work
• A motor or relay does not work
• One coil will not fire
• One flasher fires all the saucer flashers: backbox flasher feed on the wrong header
• One coil does nothing in the solenoid test
• Flasher glows full bright until the bulb blows: shorted driver transistor
• A coil does nothing although its fuse is good
• Flasher over the upper right flipper melts its plastic: the flasher is stuck on

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