So are you saying some features do activate the chimes? (if not, perhaps start there and work backwards) Chimes activated by switch closing on the 10, 100, 1000 pt relays in the back box. Sometimes someone disables the chimes if they are offensive to them (?!) check the connections to the chime unit and make sure the chime plungers are present and move freely in their coil sleeves. They can get gunked up with the cushion material used at the bottom of the plungers.