Hornby J50

In UK law the retailer is the place you send the item back to, also you can return it within 16 days if you change your mind however you have rather exceeded that already.
Caveat emptor applies, sometimes you can get a dud loco especially it seems with dcc wiring, I have 9 locos now needing some attention however Hattons are not cheap for nothing, I once sent back 5 locos to them but they allowed warranty on only 1, generally they are better than this having probably bought about 100 off them over the years I can readily testify.
In your case the J50 is a small cheap loco it depends upon the postage (return) you may be better off buying another one and leaving that first one aside until you next come back to UK, annoying but the trials and tribulations of living away, Hattons at my instigation did start in 2011 to offer DHL which to Oman I found was about half the cost of the VAT I saved, they told me it took 9 days to reach Tuavalu or similar and that was as far as they could send send anything, DHL are good but pricey when we as citizens use it, regular business gets it at about 20% of the cost we pay.

Good luck

Removing the decoder, replacing the blanking plug and retesting on DC is the natural place to start as already suggested above. If it runs then it's decoder, but let us assume it doesn't, so there's an open circuit on the loco.

If I had to suggest a single top suspect for an 'open circuit' condition on a J50, it would be failure of one of the sprung contacts below the decoder socket, that bear on the pick up wiper strips. I have these marked down as 'first to go' at the earliest hint of anything less than reliable operation from my two. Fortunately the design will make this very simple, as the access holes in the chassis casting for the sprung contacts are equally suitable for wires, soldered onto the pick up strips.

I regard the use of sprung contacts in this way - commonly seen now on both Bachmann and Hornby product - as a production line expedient, as it eliminates the need for soldering during final assembly. That must effect significant savings both in not having to train final assembly operatives in soldering, and in keeping soldering irons away from many easily melted or heat damageable plastic components. Other than this on the basis of the three mechanisms I have looked at, I would say that the design and build quality is near as good as it gets in RTR OO. In design, only a sprung axle lacking, compared to the best models we have had; and the assembly excellent, nothing to correct on any of them.

Many thanks to you all for your suggestions.

We have an unexpected public holiday here tomorrow so it will give me the time to look at the issue in more detail and try out the suggestions made.

I have already tried with the blanking plug in place and setting on DC but it is still dead.

I will report back in due course.

Thanks again

Peter

One of my (Lenz Standard) decoder fitted J50's was afflicted with intermittent stopping, which responded to a tap on the body work to resume running, and after about four months of this I finally got around to taking it off the layout yesterday evening to be prodded at in the morning sunshine. Tyres clean and shiny, all pick up wipers in contact, but what's this? All the wheelbacks where the pick up wipers run, on one side only, were dirty, and it looked like normal railhead dirt. Wiped off very easily - like regular railhead dirt - and normal service has been restored.

I can only imagine there was 'something' in a location like a checkrail or point crossing gap that was 'picked up', as there was no grease on the wheelbacks. Never seen a problem like this before. I have quickly inspected the other traction that runs where the J50s mostly operate, nothing on any of these.

Hey-ho, another one to put down to experience. Simpler to deal with than my suspicion that a spring contacter to a pick up strip had 'gone soft' and become unreliable.