An opto board does not report targets even though the optos test good.

System 11B opto board fails with good optos

Cause: From System 11B the opto processing moved off the CPU onto the opto board, which uses LM339 comparators; these fail.

Fix

• Replace the LM339 chips on the board; they are cheap enough to change all of them.

Systems

• Williams System 11B
• Williams System 11C

Related tips

• Opto switches dead all at once
• Weak or dead flippers from failing LM339s on the Fliptronics board
• Optos test good but still don't work: the opto board
• Checking an under-playfield opto board for bad LM339s
• Two LM339s on the Fliptronics board read the flipper optos
• Opto ball troughs from Indiana Jones on
• Row or column "ground short" errors
• Fliptronics: flipper coil gets hot after a while of play

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell