Well, there are only a handful of things that would cause that. First off, try running the fan motor on 1.5V from a single battery when the motor is cold. If it won't run on that, replace the motor. If it does run on that, look at the three components on the PCB, the capacitor is the top suspect, followed by the 5V regulator and then the diode. All of the parts aren't much more than a dollar, so simply replacing everything is not a bad idea if the motor is good.
The only other suspect would be the wiring and smoke switch. A long shot is the triac on the R2LC, but if that works normally and turns the smoke on and off, that isn't that likely.
