Upgrade R2/R5 and check R1/R4 in the display supply

Williams recommends changing R2 and R5 from 680 ohm to 1.2K 1/2 W for a more reliable high-voltage section. Check R1 and R4 (39K) and replace any that are off with 39K flameproof resistors.

The display supply runs at about 100 volts DC; work with the game off and the capacitors discharged.

Systems

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

Related tips

• Parts for rebuilding the System 3-7 display supply
• All score displays dead
• Lower the display voltage to 91 V to extend display life
• Score displays light then dim or flicker
• Find a shorted display glass that blows F1
• Change zener diodes Z2 and Z4 for longer display life
• Display high voltage out of range
• Score displays fade in a scrolling pattern

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