Ball one plays, but when it drains the bonus doesn't count down, no new ball is served and the ball counter stays at 1. All solenoids and relays pass the diagnostic, and the outhole switch registers in switch test. Before this, the game sometimes failed to boot or energized all solenoids at power-on.

Game stalls after the first ball: no bonus count and no new ball (faulty MPU)

Cause: The MPU board was faulty (in this case the replacement MPU that had been fitted).

Checks

• Repin the connectors and check the outhole switch registers with a ball in place during play, also with the playfield down.
• Check the board's settings for the game.
• Try another MPU.

Fix

• Replace the MPU board.

Systems

• Gottlieb System 1

Games

• Sinbad

Source: Pinball Repair help group!! (Facebook group)