Rail king imperial Hudson smoke unit heats up fine but fan quit working all wiring and plugs seem good .when I put a 9volt battery to smoke units fan runs perfectly. Does any one have any thoughts on this problem. Thanks for any help.
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The transistor or regulator (depending on which version you have) has been known to go bad. If you are somewhat handy with a soldering iron the component is available and inexpensive (less than $1). An exact model # or photo would be the next step.
Is this PS-1 or PS-2? Hopefully you unplugged smoke fan before test. Could be slipping impeller, could be bad motor. Needs to run on lower voltage, some run on 9V but won't on 4 or 5V. Could be bad circuit. If PS-1 the smoke unit has the 5V regulator which would be the problem since the resistor gets hot. On PS-2 it would be on the PS-2 board and that is more complicated. Also could be harness for PS-2, but you would also loose speed control and sounds. So what model is this? G
It's a ps-3. All other functions work ok on dcs. Thanks
I looked for Imperial Hudsons, I don't find any PS/1, so I'm guessing this is PS/2 or PS/3. Obviously, the exact model would be the way to go. 
It's a 30-1567-1 purchased 11/2014
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As I suspected, it's a PS/3 locomotive. I'd closely check the wiring from the fan motor over to the boiler PCB. If you find nothing wrong there, it's likely that the boiler PCB is defective. The good news is that's the cheap board, the tender board is the expensive one. 
An MTH tech that has the PS/3 test fixture can test the boards for you.
Thanks John
Interestingly, tender coupler won't fire now! I wonder if mth will send a pcb replacement to me. In the past they wouldn't. So I had to ship engine to them. The 5 minute snap out/snap in repair took them 7 weeks.
The tender coupler not firing doesn't sound good, that's two failures... I think it's time to have someone test the board set and see what is going on. Of course, if the board(s) are experiencing issues, it's also prudent to closely inspect all the wiring to make sure something's not killing them.
If you want to send to me I can test repair. E-mail in profile. Have you tried a factory reset? This still can be a bad fan motor. Measure ohms, is it around 11-12? Are both coupler wires attached to the coupler on the tender? G
Reset to no avail will check ohms as soon as possible coupler wires are all sound.
