A2 has no overvoltage shutdown

System 3's +5 V supply has no zener crowbar. If the regulator or the R3 trimmer shorts, well over 5 V reaches the logic and can destroy many chips. Check +5 V regularly and treat any drift seriously.

Systems

• Gottlieb System 3

Related tips

• +5 V wrong or drifting; resets after a few minutes
• Swapping A2 for a switching 5 V supply
• Checking and setting +5 V at the CPU board
• A2 and A3 plug wire colours

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)