Tester LED check of the lamp columns

Steps

• With the Leon test EPROM running, clip +5 V (TP9 on a System 6/7 CPU board, or interboard connector pin 1 at the far right) to any pin of 2J4.
• In the game, keep 2J5 and 2J7 plugged in. Connect the tester LED's plain lead to +5 V and touch its resistor lead to each 2J5 pin: it should blink in step with the CPU board LEDs.
• On the bench, touch the left leg of each pre-driver Q62-Q76 (small transistors on the right edge) instead.
• If the PIA signals are present but a column is not, check the IC13/IC14 (7408) gate inputs (the two pins either side of each output) and outputs 3, 6, 8, 11. Inputs switching but no output means a bad chip (the output pulse can be very short).

Systems

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

Related tips

• MOSFET lamp column upgrade
• Diode-test the lamp column and row transistors
• Logic-probe the lamp columns and rows
• Lamp matrix column test at 2J5 with Leon's code
• A whole lamp row or column dead or stuck on
• How the lamp matrix runs 6.3 V bulbs on 18 V
• Light a lamp row by grounding its transistor
• Diode-test the lamp 7408 and 7406 chips

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