The flippers do not work during a game.

Flippers dead in a game

Cause: Flipper power runs only through the two normally open contacts of the Q (game over) relay in the lower cabinet, which the CPU holds in through driver MosFET Q32 (Sol.31) during play.

Checks

• Start a game and see whether the Q relay pulls in.
• If it pulls in, check its two contacts close and are clean.
• If it never pulls in, test Q32 on the driver board.

Fix

• Clean or adjust the Q relay contacts, or replace a faulty Q32 MosFET.

Systems

• Gottlieb System 3

Related tips

• Testing a dead coil or flasher
• A whole row of eight switches dead
• The A15 flipper sensor board
• Spare MosFETs for the driver boards
• Logic chips worth stocking
• What the A3 driver board drives
• Lamp and switch matrix size and drivers
• All System 3 games use Gottlieb's thin flippers

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