A controlled lamp (such as shoot again) is lit all the time, or a coil such as the ball release locks on when a game starts.

A CPU-controlled lamp or coil stays on

Cause: A failed MPS-U45 driver on the driver board.

Checks

• Diode-test it from base to each leg. Example faults: 0.7 collector and 0.5 emitter (should be 1.3), or 1.2 on one leg and nothing on the other.

Fix

• Replace the MPS-U45 (or use a CEN-U45).

Systems

• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B

Related tips

• System 80 driver board transistor types
• Flippers dead during play: check the "U" relay
• Haunted House trap door won't open
• How driver board coil transistors are switched
• Backbox chase lights not running
• Coils lock on and burn because of the Gottlieb ground fault
• Run the System 80 lamp (16) and solenoid (17) tests
• First power-up, step 5: add the driver board, then coil power

Source: Repairing & Upgrading Gottlieb System 80 Pinballs from 1980 to 1989, Part One, Clay Harrell (pinrepair.com)