my reloader b did this, melted the shell, fried the board, and melted the wires and connector going to the motor... was because it was ever so slightly pathetically raining and i replaced the batteries. think i may have got a teeny bit of water in there.
if you haven't got to this stage yet, then id tell you to take all the internals out, make sure there is no water or slight damp anywhere. if when you turn it on again, it does the same, buy a new board and motor...
and nige... when i noticed mine smoking in at training, i could've done with one of those! it only stopped smoking about 30mins after id disconnected the motor and batteries from the board. ill get a picture of it, i know i have it somewhere