Use C6 negative as ground when measuring 60/42 V

The +60 and +42 V display supplies have their own ground. When reading them with a meter, put the black lead on the negative lead of the big C6 (200 mfd 150 V) capacitor rather than on another ground point.

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

• Score displays flicker or go dim
• Power supply bring-up, step 3: displays
• +60 V or +42 V display voltage missing
• The mandatory System 1 ground modifications
• Why System 1 coils lock on: the ground shift
• System 1 power supply shows about 110 V where 4 V and 8 V belong: wrong ground
• Quick checks on the similar System 1 power supply
• Spare transistors for System 1 boards

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