After a target was smashed and stuck, the game reports an opto fault at boot and none of the opto switches register in switch edges. The regulated 12 V test point reads fine, but the LED on the opto board is off.

Every opto dead and the opto board LED off: failed bridge BR5 for the unregulated 12 V

Cause: The optos run on the separate unregulated 12 V supply on the power driver board, which has only a bridge rectifier (BR5), a filter capacitor and a fuse. The bridge had failed.

Checks

• Check the LED on the opto board: off means no unregulated 12 V (or a broken wire or unplugged connector).
• Measure the grey-yellow wires to the opto boards; a working supply reads about 14 V.
• Check that supply's fuse first, then the bridge rectifier; replace the filter capacitor only if it is bulging.

Fix

• Replace bridge rectifier BR5 on the power driver board.

Systems

• WPC-Security (WPC-S)

Games

• Indianapolis 500

Related tips

• 'Check F114 and F115' with switch 24 open: missing 12 V, bad bridge BR5
• WPC-89/WPC-S driver board LEDs and test points
• Driver board LED1 off (+12 V regulated missing)
• Driver board LED4 off (+5 V missing, game will not boot)
• Driver board LED7 off (+12 V unregulated)
• Driver board LED1 off: switch matrix 12 V missing (WPC-S and earlier)
• Driver board LED7 off: unregulated 12 V missing (WPC-S and earlier)
• Shorted or open bridge rectifiers

Source: Pinball Repair help group!! (Facebook group)