Output voltages wander, read high, or the overvoltage protection trips.
Power supply voltage drifts or overvoltage trips
Cause: Dust in the two 1K trimmer pots: R4 sets +5 V and R16 sets +60 V.
Fix
- Clean the trimmers with contact cleaner, or better, replace them with new 1K pots and readjust.
Systems
Related tips
- Display high-voltage section of the power supply
- No +5 V or only 2.4 V from the power supply
- System 1 power supply outputs
- Power supply output connector pins
- Replacing power supply filter capacitor C1
- Overvoltage protection on the logic supplies
- System 1 power supply shows about 110 V where 4 V and 8 V belong: wrong ground
- Getting to the power supply solder side
Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)