Nothing to do with a fuse. the smell and cracking, will be electrical arcing, but could be in several components, filter capacitor, (but why about same time) motor ( again would expect it at different times) speed controller is possibly the 1st to go for, after unplugging unit, remove back, and have a sniff around. Fault finding, is not just about using a test meter. you should be able to limit the area by smell. once you find where, next is why, if the smell takes you to the speed control pcb, look at it, you might see the arc point, look around, any signs of water, streaks etc, same for any other location
SD, February 2012