A group of controlled lamps stays on, brighter than normal, instead of flashing in attract mode or the all-lamps test.

A row or column of lamps stuck on and very bright

Cause: A shorted lamp matrix transistor holds that row or column on full time at +18 V.

Checks

• Check the bulbs and fuses for lamps that are out.
• Look up the stuck lamps in the manual; see whether they share a row or column.
• Test the transistor for that row or column.

Fix

• Replace the shorted TIP42 (column) or TIP122/102 (row).

Systems

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

Related tips

• Lamp matrix fault with good transistors: 0.4 ohm resistors
• Testing lamp matrix columns with a test socket
• Testing lamp matrix rows with a test socket
• Whole lamp column works only intermittently: reflow the board header
• Quick lamp row test: ground the row driver tab
• Lamps in two columns light together in single lamp test: failed lamp column transistor
• System 11 lamp matrix basics
• Lamp matrix still wrong after replacing transistors: upstream parts

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