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

Fixing a dead switch column on the CPU board

Cause: Usually the column's 2N3904 (Q42-Q49). Less often the 1.5k resistor (R71-R78), the 4.7k network SR15, the 74LS244 at U40 or the PIA at U38.

Checks

• Test the column transistor.
• Check the 1.5k resistor for that column.
• Measure SR15 pin 1 to each of pins 2-10: about 4.7k each.
• Column paths: 1J8-1 Q45/R77/SR15-2; 1J8-2 Q49/R78/SR15-3; 1J8-3 Q44/R75/SR15-4; 1J8-4 Q48/R76/SR15-5; 1J8-5 Q43/R73/SR15-7; 1J8-7 Q47/R74/SR15-8; 1J8-8 Q42/R71/SR15-9; 1J8-9 Q46/R72/SR15-10.

Fix

• Replace the bad transistor, resistor or network.
• If those test good, replace U40 (74LS244), then the 6821 at U38 last, or prove the PIA with a test EPROM first.

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
• Switch column (drive) circuit on the CPU board
• One switch column dead: parts to check in order
• Whole switch column dead after working under the playfield
• Row or column error: CPU board or playfield?
• Inlane, outlane and drain switches all dead: blown switch transistor Q49
• Flipper button resets the game or a slingshot tilts it

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