One day both my doorbell and the one for my tenant stopped working. I figure that the transformer needs to be replaced. I purchased a new one. My transformer is bolted to the bottom of the fuse panel. I removed the cover and saw that there are 3 wires, 2 black and a green. The green is wired to ground, one of the black is piggy backed to a fuse(the wire is split with a connector in the middle, see pic) and the second black is screwed into a panel that is fiilled with screws. I really do not know what that screw filled panel is for. Here is a pic, I have pointed out, with a pencil, the screw that I am unsure of. Can anyone guide me in the right direction as to how to proceed to replace the transformer?

