The CPU display or LEDs stay on although the game runs normally.

System 7 diagnostic display stays lit on a working game

Cause: IC2 (74125) has shorted inside.

Checks

• Confirm the game boots and plays normally.

Fix

• Replace IC2 (74125).

Systems

• Williams System 7

Related tips

• A System 7 CPU board can run any System 3 to 7 game
• Run a System 6/7 CPU board on +5 V only
• Which CPU boards can run which system firmware
• Why the CPU LEDs stay on when the program does not run
• Board boots and passes SW1, but no displays or CPU lamps
• System 7 CPU LEDs are swapped versus System 6
• Late System 7 CPU boards lack LEDs and DIP switches
• Is it the CPU board or the driver board? Boot the CPU alone

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Two, Clay Harrell (pinrepair.com)