Lamp matrix problems remain after replacing the TIP42 and TIP122 and checking the matrix resistors.

Lamp matrix still wrong after replacing transistors: upstream parts

Cause: A failed column pre-driver or logic chip, or a row SCR or its driver.

Checks

• Columns: 2N6427 pre-drivers, the odd numbers Q51 to Q65, then 7408 chips U52 and U53, then PIA U54.
• Rows: 7406 chips U55 and U56, which drive 2N5060 (NTE5400) SCRs S1 to S8, then PIA U54.

Fix

• Replace the failed part.

Systems

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

Related tips

• Lamp and switch matrix transistor positions on the CPU board
• Lamp row still dead after a new TIP122
• Lamp column still dead after a new TIP42
• Lamp matrix fault with good transistors: 0.4 ohm resistors
• Test a 2N6427 (MPSA14) lamp matrix transistor with a meter
• Test a 2N5060 lamp matrix SCR with a meter
• An LED stays dark on a lamp header during the test
• Lamp driver SCRs on the CPU board

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