Dear forum,
After owning this otherwise excellent Märklin model (37984, Union Pacific Class 800, a dynamic smoke generation product) for a couple of years without any issues, I appear to have caused a smoke generation malfunction by mistakenly using the wrong smoke fluid (02420 instead of the correct 02421), or so I suspect. I’ve been unknowingly using the incorrect fluid once or twice a year since I bought the product a couple of years ago without noticing any problems. Last night, the locomotive again ran flawlessly with smoke generation on for a minute or so, before I switched the function off.

At that point, excessive amounts of smoke boiled off, and as I turned the function on again, there was this strange burnt smell as well as a weird electric noise coming from the locomotive. After only a few seconds of running with these issues, the circuit/mobile station powered down. If I try to run the locomotive again with smoke generation on, the problem repeats as above. With smoke generation off, there appear to be no issues (every other function works as it should).

After doing some basic research, it appears that using the wrong smoke fluid could cause issues with this product, and I’m worried I’ve broken something because of my mistake. I didn’t appreciate the difference between the different smoke fluids and thought them to be essentially the same product. The warranty has probably expired (in any case, the receipt is gone since I moved house), do you think a dealer or Märklin themselves could repair the locomotive (I expect that I should have to pay for the service)?

You might have a damaged "controller board" also....
Ref: https://www.marklin-users.net/forum/posts/m657105-Marklin-37984-Shorting-out-CS3#post657105

You can get the smoke generator as a spare part E353931, but the controller board is not included. and it seems that it's not available? as a spare part for normal consumers.

Hello,
I had the same issue also three friends had the same problem. The board that controls the dynamic smoke unit shorts due a failure in their components. The problem is that the spare part is not indicated in the part list, only the smoke unit wich is another part.

I live in Chile and in my case I was able to contact customer support of Märklin USA and they helped me selling to me the part (board and just in case I also changed the smoke unit).

Another friend here in Chile, was able to contact Märklin service in Germany and he explained his situation that the locomotive was too far away from Germany and was going to be too expensive to send the locomotive and then return it, so Märklin Service Center send to him the board free of charge.
I reccomend you to contact your Märklin Dealer and ask if he can request the part or try to contact Märklin Service center.

Kr,

Eduardo