The -12 V section and what it feeds

Two 14 V AC windings are rectified by CR3/CR4, filtered by C4 and held at -12 V by a 7912 regulator. It feeds the spider chips and the coil drive reference on the stock CPU board; a Ni-Wumpf replacement CPU does not use it.

Systems

• Gottlieb System 1

Related tips

• Display high-voltage section of the power supply
• Logic and display reference section of the power supply
• 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 diodes, capacitors and other parts for System 1
• System 1 power supply outputs
• The 5/12 V supply is only half-wave rectified
• Getting to the power supply solder side

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