Neale,
When I was a lad power transistors (at least the radio frequency ones) were described to me as "the fastest fuse on three legs". In practice these things often fail as a short circuit which is what takes out the fuse to protect everything else as you say. Doddy's got an evening amusing himself with his soldering iron out of it so all's well that ends well.

Putt's Law states that technology is dominated by two types of people. Those who understand what they do not manage and those who manage what they do not understand.