One switch row fails the clip-lead or logic-probe test.

Fixing a dead switch row on the CPU board

Cause: A bad row network (SR11 560 ohm, SR9/SR10 1k), a bad 4011 at U30 or U39, a bad SR14 pull-up, or the 6821 PIA at U38.

Checks

• Measure SR11 pin 1 to pins 2-10: about 560 ohms each.
• Measure from the 1J10 pin through to the second SR9/SR10 pin for that row: about 1k.
• Check continuity onward to the 4011 input. Row paths: 1J10-1 SR11-2 SR10-1/2 U39-12 (row 8); 1J10-2 SR11-3 SR10-3/4 U39-8 (row 7); 1J10-3 SR11-5 SR10-5/6 U39-2 (row 6); 1J10-5 SR11-6 SR10-7/8 U39-5 (row 5); 1J10-6 SR11-7 SR9-2/1 U30-13 (row 4); 1J10-7 SR11-8 SR9-4/3 U30-9 (row 3); 1J10-8 SR11-9 SR9-6/5 U30-2 (row 2); 1J10-9 SR11-10 SR9-8/7 U30-6 (row 1). Pin 4 is the key.
• With 1J10 unplugged, both 4011 inputs for each row should be high and its output low; a logic probe confirms this.

Fix

• Replace the bad network or the 4011 (U30 rows 1-4, U39 rows 5-8).
• If all of that tests good, replace the PIA at U38 or prove it with a test EPROM.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Switch matrix dead after an under-playfield adjustment with power on
• System 11 switch matrix: connectors and chips
• One switch row dead: parts to check in order
• Whole switch column dead after working under the playfield
• Displays out, flippers and ball eject dead after display glitches
• F-14 Tomcat: left credit-display character scrambled
• Testing the switch rows with a clip lead
• Switch row (return) circuit on the CPU board

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