Light a lamp row by grounding its transistor

Steps

• Switch on; set the coin door switch to manual-down and press Advance twice so the displays show zeros.
• Clip a lead to ground (the backbox ground braid or interboard connector pin 40).
• Touch the other end to the tab of one row transistor (Q47, Q49 ... Q61, the vertical row near the middle of the driver board). All eight lamps of that row should light.
• Note any that do not and look them up in the manual; check whether the dark ones share a column.
• This checks the wiring and lamps, not the transistors.

Do not do this on the column transistors: it will blow the lamp matrix fuse.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Diode-test the lamp column and row transistors
• A whole lamp row or column dead or stuck on
• Tester LED check of the lamp rows
• Logic-probe the lamp columns and rows
• Lamp matrix row test at 2J7 with Leon's code
• Lamp rows stuck on: the 7406 at IC19
• How the lamp matrix runs 6.3 V bulbs on 18 V
• Tester LED check of the lamp columns

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)