If you cracked the case I know it would void our warranty. But ours are riveted shut. Some manufacturers prefer to just screw theirs closed. If the wires to the core are charred then the core is shot. It may still work but I know we would throw it away. The core itself should never go bad unless it burns up. BUt I would concur with Steve....Meltdowns occur 99% of the time due to BAD CONNECTIONS producing Arching!!!