In the lower picture, that unit should have been mounted with the fins going vertical, so the heat rises away from the unit. The gold colored, finned aluminum cover is removable without removing the unit from the wall. As I recall, the domed top nut holds it in place. Under the cover is a fuse that may need replacing.
For help from the Bose people, the phone number for the Invisable Built-In system is 1-800-996-2673.
Larry