I managed to kill one PC floppy drive by switching the motor that rotated the disk and not switching it off (because my crash handling was nonexistent and floppy read routine I was writing crashed somehow). I guess the disk rotation motor (or its switching circuitry) overheated (after all, it was supposed to be used with a reasonably low duty cycle): the drive would no longer rotate the floppy (so I could also not tell if the rest of the drive still worked).