Measure the blanking signal
Steps
- Fit the game ROMs and power the boards on the bench.
- Meter on DC volts at interboard pin 37 (fourth pin from the left) on the driver board: expect 4 to 5 V after boot.
- If it is low, measure at CPU connector 1J3 pin 4.
- Good at 1J3 pin 4 but low at pin 37: the interconnector is bad. Low at both: the blanking circuit or what drives it is at fault.
Systems
Related tips
- What the blanking signal does
- Add a blanking LED to a driver board
- Solenoid fuse blows at power-on and solenoids fire: driver board logic chips
- Slings and pop bumpers feel sluggish: backbox boards loose with missing mounting screws
- Slings and pops all burned at once: CPU lock-up from the 40-pin interconnect
- System 6 and System 7 driver boards can be swapped for testing
- Coil locks on and new transistors don't help: a failed 7408 on the driver board
- Kicker coil locks on again after a new TIP122: dead 7408 gate on the driver board
Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)