Lamp matrix problems remain after the row and column transistors test good.

Lamp matrix fault with good transistors: 0.4 ohm resistors

Cause: One of the eight 0.4 ohm 3 W sand resistors at the lower right of the CPU board (R113, R116, R119 and R122, plus R125, R128, R131 and R134) has desoldered itself from heat or fallen off.

Checks

• Inspect and measure each of those resistors and its solder joints.

Fix

• Resolder or replace the resistor.

Systems

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

Related tips

• Lamp matrix still wrong after replacing transistors: upstream parts
• Testing lamp matrix columns with a test socket
• Testing lamp matrix rows with a test socket
• System 11 lamp matrix basics
• A row or column of lamps stuck on and very bright
• Lamps in two columns light together in single lamp test: failed lamp column transistor
• Whole lamp column works only intermittently: reflow the board header
• Row or column error: CPU board or playfield?

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Two, Clay Harrell (pinrepair.com)