Optos all read closed, odd behavior at power-on, for example an opto-sensed kicker firing over and over.

Optos all read closed at power-on: blown opto supply fuse

Cause: The unregulated 12 V fuse (usually F116 on WPC-S and earlier, F109 on WPC-95) has blown, so the opto emitters are dark while the receivers still work and read closed.

Checks

• Check F116 / F109.

Fix

• Replace the fuse and find out why it blew (see BR5).

Systems

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

Related tips

• Opto switches flicker open and closed in switch test
• Opto switches dead or intermittent: check the 12 volt supplies
• Check fuses F106/F101 with no lamps and no game start: shorted bridge diode
• 12 V and 50 V supplies read far too high: transformer line-voltage jumpers set wrong
• WPC power driver board fuses and what they feed
• Typical causes of each blown fuse (WPC-89 and WPC-S)
• Typical causes of each blown fuse (WPC-95)
• A coil keeps firing at power-on and the DMD is blank

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