How to tell a System 11C CPU from an 11B
System 11B and 11C CPU boards share the part number D-11883-xxx. An 11C board has empty or missing positions at U21 and U22 (no sound EPROMs), because its sound moved to the sound board.
Systems
Related tips
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Source: Repairing Williams System 11 Pinball 1986 to 1990, Deel 1, Clay Harrell (pinrepair.com)