Add a blanking LED to a driver board

Steps

• Solder the round-side (anode) lead of an LED to interboard pin 37 on the driver board.
• Join the flat-side lead to one end of a 150 ohm, quarter-watt resistor.
• Solder the other resistor lead to the wide ground trace around the board edge.
• At power-on the LED should stay off for a moment, then light and stay lit when blanking is good.

Systems

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

Related tips

• Build a tester LED for PIA and driver checks
• Making the test LED for the test EPROM
• Use the tester LED, not a logic probe, for driver board tests
• What the blanking signal does
• System 6 and System 7 driver boards can be swapped for testing
• Hyperball driver board is unique
• Driver board transistors and what they drive
• Measure the blanking signal

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