Fixing the burnt lamp matrix resistors R149-R156

Steps

• Remove the driver board.
• Replace the eight R149-R156 resistors with 27 ohm 5 W wirewound (sand or ceramic) resistors.
• Mount them about 1/4" above the board for air flow.
• Use #47 bulbs for the feature lamps, which cuts lamp current by about 40%.

Systems

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

Related tips

• Replace burnt 3 watt lamp resistors with 5 watt
• Burnt 27 ohm lamp matrix resistors R149-R156 on the driver board
• How the lamp matrix runs 6.3 V bulbs on 18 V
• Lamp matrix column test at 2J5 with Leon's code
• Lamp matrix row test at 2J7 with Leon's code
• Lamp matrix wire colours and connector pins
• Tester LED check of the lamp columns
• Tester LED check of the lamp rows

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