WPC alphanumeric display board high-voltage checks

On Funhouse, Harley-Davidson and The Machine, J307 pin 1 carries 85 to 90 V AC (pin 4 is its AC reference) from which plus and minus 90 V DC are made; J306 pin 1 is +5 V DC and pin 3 ground. The same fixes apply here: 39k resistors R48/R49, zeners D5/D6 to 1N4763, and 3.9 V zeners D1/D2.

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

• WPC Alpha-Numeric

Related tips

• Gas discharge displays need high voltage
• Alphanumeric display board numbers
• WPC display and DMD controller board versions
• Alphanumeric WPC games: weak or dead score displays
• Alphanumeric display segments or digits missing

Source: Repairing Williams System 11 Pinball 1986 to 1990, Part Three, Clay Harrell