The majority of modern sounds including the background audio (when book-keeping #18 is set to "03") come out of the AD558 Digital to Analog Converter (DAC) chip at U10 on the S&T board. Suspect the 2.0uF capacitor C43 (common failure and goes open circuit) which feeds the output of the DAC to the pre-amp. In fact you're probably better off getting a capacitor kit and changing them all on this board - the caps on these S&T boards are known to go bad.

The fake chimes are produced by the AY-3-8912 sound generator chip at U12. The AY-3-8912 also produces the modern sound effects for the "DELUXE" standup targets behind the 1-7 drop target bank, but most of the other modern sounds come out of the DAC.