Lower the display voltage to 91 V to extend display life
Swap zeners ZR2 and ZR4 from 1N4764A (100 V, 1 W) to 1N4763A (91 V, 1 W). The displays become slightly dimmer but last much longer, which matters because replacement glass is scarce. Skip it if a display is already marginal and outgassing, as it may stop glowing.
The display supply runs at about 100 V DC (plus and minus) with large filter capacitors; work with the game off and unplugged, and measure live only with insulated probes.
Systems
- Williams System 3
- Williams System 4
- Williams System 6 / 6A
- Williams System 7
- Williams System 9
- Williams System 11
- Williams System 11A
- Williams System 11B
- Williams System 11C
Related tips
- Rebuilding the +100 V section of the power supply
- Rebuilding the -100 V section of the power supply
- Fit 91 V zeners at Z2/Z4 to extend display life
- Change zener diodes Z2 and Z4 for longer display life
- Display high voltage out of range
- Upgrade R2/R5 and check R1/R4 in the display supply
- High-voltage fuse blows once the display connector is plugged back in
- Displays blank but the game plays
Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell