With a replacement combination CPU/driver board fitted, the game boots fully and takes credits, but keeps making the tilt (groaning) sound and won't start a game. Unplugging the sound board's input plug stops the noise.

Tilt groan at power-up and no game starts: replacement board DIP switch half set

Cause: One of the replacement board's game-selection DIP switches was not fully switched, so the board was not set up for this game and kept sending the tilt sound.

Checks

• Unplug the sound board's input plug: if the noise stops, the CPU/driver board is commanding it.
• Check the driver board connectors are on the right headers.
• Check every DIP switch on the replacement board against its instructions for this game, and make sure each one is fully in position.

Fix

• Set the DIP switches correctly and firmly.

Systems

• Williams System 6 / 6A

Games

• Disco Fever

Related tips

• No sound in play or solenoid test, and grounding inputs does nothing
• Using the sound board test switch
• Powering a sound board for testing
• Sound self-test passes but some game sounds never play: bad PIA on the sound board
• Replacement CPU board: game won't start though tests pass: DIP switches reversed
• Type 1 and type 2 sound boards and their switches
• Test the sound board inputs one at a time
• What the power supply board takes in and puts out

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