Check that the cardan shaft leading to the front drivers has not come out of the gearbox. If it has, you should be able to put it back in, carefully, with a pair of angle nosed pliers.

I have had this happen a couple of time with my Marklin 37993 Big Boy, I assume the Trix has similar construction.

It should be fairly straightforward. Just follow the diagram in the instruction manual. AFAIR there are two or three small phillips screws to be removed.

The question isn't whether the Cardan Shaft has fallen out (it undoubtedly has) but why it falls out.

I had the same problem on my 37990 Bigboy and it turns out there was a whole batch of them came out of the factory missing the retaining screw that holds the front "engine unit" into the frame. Without that screw, the front driving wheel assembly is free to flop about all over the place (it doesn't fall out) and on curved track it can pivot so far that the cardan shaft drops out. Being a worm drive system, without the drive shaft the front wheels just lock up.

The following applies to the 37990 Bigboy (which is the one I have) but it'll probably be pretty similar for all. Here's how to check whether that screw is in place correctly or not:
With the body shell lifted off as per the manual, you can see the rounded top of the motor housing midway between the two sets of driving wheels. In front of that there is a small circuit board (NOT the decoder one) with not much on it. The drive shaft for the front wheels is underneath the rectangular plastic housing that circuit board is mounted on.

Remove the single screw that holds the front circuit board onto the rectangular plastic housing it is mounted on, and also remove the screw in front of that plastic housing that holds the metal contact springs for the smoke units. This also releases that rectangular plastic housing (and the front half of the "running boards")
You might need to unclip the wires from the top of that plastic housing to enable the rectangular plastic bit to lift up and swing aside enough to see beneath it.

The plastic drive shaft can be clearly seen (on mine it had just fallen out of the retaining "cups" at each end (one on the motor and one on the gear box).

Directly beneath that drive shaft is (or should be) the head of the shoulder-screw that goes down into the rear end of the front driving wheel frame. Make sure you check that screw.
In my case the screw was actually rattling around inside the packaging for the loco which helped immensely because I didn't have to worry about where to get another, but if you're not fortunate enough to actually have the screw then I guess we'll need to try and figure out the part number. I've just been perusing the parts diagram trying to work that out, but it isn't immedialty apparrent - Need to do a bit more research on that.

Anway, having got the screw it's just a question of putting it all back together. It can be a bit tricky to get back into place and I think the proper assembly sequence would be front frame retaining screw, and then drive shaft and motor, but I managed to get mine back together the other way round with the motor screws loosened off a bit. If the drive shaft has come out you'll maybe want to loosen the motor screws anyway to get it back in. (I didn't want to move the motor too much 'cos I was scared of the back drive shaft also falling out while I had the motor loose.)

Once you've done that it'll run like a dream and you should have no more problems

Have fun

Dennis

Wow, When I first got my Big Boy there was indeed a screw rolling around in the box. I might have even noted it on this forum. I'll have to look for it in the box again.

Thanks for the descriptive procedure. It makes me a lot more comfortable taking it apart.

Thank you both for your help. I hope to have a chance to try this later today.

Bill

Something is certainly lacking somewhere. I can sort-of accept that a whole batch of (say) the original Bigboys might have had a problem, but you saying that you had the same problem on your 37993 - which came out a year or 3 later thean the 37990 certainly did shock me. There was enough fuss made at the time about all the Bigboys with screws dropping out of them, and there's no way they can't have known about it. And I don't believe they just worked loose in the shipping process either:- Marklin have been using that sort of screw for that sort of application since time immemorial and I've never heard of that happening before. Sad, really.


Bill,

Glad you got yours sorted alright finally. Excellent news

cheers
Dennis

Maybe Marklin should be advertising on the box - "Some assembly required."

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Dennis, I found the screw fitted exactly into the place where you said it would. I find it really bad, that after having this sort of problem with the 37990, they repeat it with the 37993.

Jack your ideas up Märklin!