System 11A-11C CPU LEDs: normal state
Three LEDs near the middle of the board. Left ("+5 vdc"): always on when +5 V is present. Middle ("diagnostics"): flashing continuously in attract mode. Right ("blanking"): always on when the blanking circuit has released.
Systems
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Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)