Most solenoids and CPU lamps are stuck on, or no solenoid works at all.

Many coils and lamps on, or no coils working

Cause: -12 V missing at the CPU board, or failed CPU buffers Z6/Z7 (7417).

Checks

• Measure -12 V across CPU C17.
• Then test Z6/Z7 as in the 7417 test entry.

Fix

• Restore -12 V or replace the bad 7417.

Systems

• Gottlieb System 1

Related tips

• Firing coils from CPU buffers Z6 and Z7
• Why System 1 coils lock on: the ground shift
• All coils and most CPU lamps lock on at power-up
• Early driver boards lack isolation diodes
• System 1 CPU board connectors
• Aftermarket System 1 CPU boards
• CPU connectors that fail most
• The CPU to driver board harness

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