This is the procedure to activate the background sweep sound for Williams Stellar Wars. By default this sound is disabled.
1. Press 9 to enter diagnostic mode. The displays should go blank when this key is pressed.
2. Press 8 to enter test mode.
3. Press 7 then press 8 to see 01 in the credit display.
4. Continue to press 8 until you see 04 in the credit display and 35 in the match/ball in play display.
5. Press the 1 key to change the value (value can be anywhere between 00 and 31, if value is 00 then the sweep sound is off)
6. Press F3 to save your changes and reset the table
According to the manual, this setting should be set to 30. Most arcades though set the sound to 01. Try any of the settings to find the one that you would prefer.