The lamp PIA IC10 rarely fails
Rule out the lamp driver transistors and the 7406/7408 gates before suspecting the 6821 lamp PIA at IC10. Testing it properly needs the Leon test EPROM and a tester LED; if done in the game, remove F2 and F3 and unplug 2J4, 2J5 and 2J7 first.
Systems
Related tips
- How the lamp matrix runs 6.3 V bulbs on 18 V
- Tester LED check of the lamp rows
- MOSFET lamp column upgrade
- 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 column test at 2J5 with Leon's code
- Lamp matrix row test at 2J7 with Leon's code
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)