Pretty confident its not going to be a CVSD chip. The PIA sents digital data to the CVSD and it spits out voice which the 1458's mix with the sound effects then it sends the mixed sound and speech back over to the sound board to be amplified for the speaker.

Sounds like you have a digital failure, not analogue. Something like the sound trigger nputs from the mpu/driver are not getting read right by the sound board's computer. Make sure the connectors are good. You can put the game in sound / solenoid test and watch the signals go through the 4049/4050 buffers. Make sure you get a low pulse for every wire to the sound board through the buffer chip. It may take the board getting warm for the connector to get flaky. Don't forget the mpu/driver side connectors too.

CVSD failures in my XP is garbled speech or silence when speech should be playing. *** this cvsd chip is easily damaged by ESD, ive blown one being careless ***