Every controlled lamp on one lamp matrix column (the yellow-black wire) stays dark, with the wiring traced good back to the board connector.

A column of controlled lamps out: failed lamp column transistor Q60

Cause: The column drive transistor for that column, Q60 (a TIP42), had failed.

Checks

• Use the lamp matrix chart to confirm the dead lamps share a column wire.
• Check the board connectors for that column first, since burnt header pins are common on this game.
• Test the column transistor and compare with its neighbours.

Fix

• Replace Q60 (TIP42) and repair any burnt connectors or header pins.

Systems

• Williams System 11B

Games

• Taxi

Related tips

• Lamps in two columns light together in single lamp test: failed lamp column transistor
• How the CPU-controlled lamp matrix is wired
• Test a TIP42 lamp column transistor with a meter
• Diode-test the lamp column and row transistors
• Lamp and switch matrix transistor positions on the CPU board
• Lamp matrix column test at 2J5 with Leon's code
• Test each lamp column driver with a test lamp
• CPU and driver board transistors by position

Source: Pinball Repair help group!! (Facebook group)