Some lamps along one row or column never light.

Part of a lamp row or column stays off

Cause: A broken wire in the playfield daisy chain or between the playfield and the driver board.

Checks

• Use the lamp location chart and lamp matrix table to find which row or column is affected and its wire colour.
• Check that wire for continuity lamp to lamp and back to the board.

Fix

• Repair the broken link.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• A lamp row very bright or dead
• A lamp column or row stays on all the time
• One insert lamp dead with a good bulb and socket: diode on the lamp board
• Lamp lights twice or two lamps act as one
• Lamps light twice in the all-lamps sweep, or two lamps act as one
• A few unrelated lamps never light
• One controlled lamp out while the rest of the matrix works
• Testing lamp-row drivers with a test lamp

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer