Quoted from ryanwanger:Helpful responses so far. Thanks!
Can a transistor catch fire like that when it goes bad? Or does something else need to be wrong to cause that?
Actually it would probably be one of the resistors that caught fire and burned up. This is likely the result of the driver transistor being shorted.
I would pull the driver board, clean up all the soot with some isopropyl alcohol or similar and replace all of the parts associated with that transistor - in this instance, I would also replace the driver IC because there has been some serious current flowing there and I would be suspicious of its well being.