DVD pic but no sound with ZX75 player

[aberg]

We've a ZX75 in our new Catalina 22FB. We get sound when playing the radio, but when we tried to watch a DVD, we got pic on TV but no sound

Apart from switching our Samsung TV over to AUX mode (which we did), do we have to go thru some kind of set up/switch over on the DVD unit? We just assumed you could pop in a DVD and it would work. It does play the pic, but just no sound. The manual is of no help, but does the MODE function need to be set to DISC, whether it's CD or DVD for it to play properly??

Thanks!