Tester LED check of the lamp rows

Steps

• With +5 V on any 2J4 pin and ground on any 2J6 pin (in the game, just leave 2J6 plugged in), connect the tester LED's plain lead to +5 V.
• Touch the resistor lead to each 2J7 pin: it should blink with the CPU board LEDs.
• If a pin is dead while the IC10 PIA signals are fine, check the IC19 7406 outputs (even pins 2-12) and IC12 outputs on pins 2 and 4. No output means a bad chip; a good output means a bad row transistor or pre-driver.

Systems

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

Related tips

• Diode-test the lamp column and row transistors
• Light a lamp row by grounding its transistor
• 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
• A whole lamp row or column dead or stuck on
• How the lamp matrix runs 6.3 V bulbs on 18 V
• MOSFET lamp column upgrade

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