Is this a PS-3 loco? If so make sure you have a good connection between engine and tender with the wireless drawbar. If that is fine, remove the engine shell and examine the wiring to the smoke unit making sure nothing is pinched, damaged. Carefully remove the 32pin connector from the boiler board by the connector not pulling wires, and reseat it after ensuring no pins are bent. If the fan motor still runs on it's own I would think the boiler board has a shorted fet and needs to be replaced.
If this is a PS-2 3V engine. The above doesn't apply, but I would still inspect engine wiring, but you will also have to look inside tender. What model #? G
