I come across burnt wire nuts all the time also. The installer gets in a hurry & doesn't pre twist the wires before twisting the wire nuts. An very old master electrician taught me well 30 years ago to make the connection strong & tight before installing the wire nut on connection. The board more than like was damaged do to the wire nut connection arcing from the sloppy install & thus when re-energized went to smoke it self. My 2-cents.