just my keen observation, but SHOULDNT this be half his problem and half yours? anyway i dont even know what it is, or care really, but any good roommate should be willing to offer to help pay some of the damage, as well as you should be willing to accept that leaving it out, caused half the problem. anyway, if things don't work out that way youll just have to decide whats more important, a roommate you like or a repair bill.. after all im sure it was an accident.
stuff like this comes up in small claims court all the time.. its like one guy a leaving a live bomb in the living room, and the second guy is then held responsible because he didnt "tip toe" around the potentional probelm the first guy created.
anway - if its something expensive im sure it can fixed, if its not worth just buying a used one to replace it.