Display high-voltage section of the power supply

69 V AC is rectified by CR6-CR9 (1N4004) and filtered by C6 (200 mfd 150 V). Q2 (TIP31C) regulates with Q4 (MPS-A43) and 12 V zener CR11 (1N4742); Q3 (2N3416) and R13 (33 ohm) limit current. R16 (1K) sets 60 V. An 18 V zener, CR12 (1N4746), drops this to 42 V for the credit display, so the 42 V rises when displays are unplugged.

The display supply runs at 60 to 69 volts; work on it with the game off and never plug or unplug display connectors with power on.

Systems

• Gottlieb System 1

Related tips

• Power supply voltage drifts or overvoltage trips
• System 1 power supply outputs
• Replacing power supply filter capacitor C1
• Getting to the power supply solder side
• Power supply bring-up, step 1: inputs
• Power supply output connector pins
• Quick checks on the similar System 1 power supply
• Power supply bring-up, step 2: CPU load

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)