Perfect on DC but not DCC

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smokebox
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Joined: Wed Jun 28, 2017 5:28 pm

Perfect on DC but not DCC

Postby smokebox » Fri Apr 26, 2019 9:26 pm

I have a new Standard class 4MT (2-6-0) that runs perfectly on DC with the blank chip and it's been run in. When I plug the decoder in (Hattons 6 pin) and run on DCC, it will go in the required direction but for only about half an inch or a couple of centimeters. It will do this maybe 3 or 4 times and then give up altogether. If I unplug the controller and then start again, the same thing happens. I ordered a new decoder chip from Hattons and the same thing happens so I guess it's not the decoder. Two other locos run with no problem.
Anyone have any thoughts about this? Thank you

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Mountain
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Location: Somewhere in Wales, UK.

Re: Perfect on DC but not DCC

Postby Mountain » Fri Apr 26, 2019 9:45 pm

It could be the decoder. Having said that, I had a DCC decoder which seemed to be causing issues. The train would go and then stop and go and then stop. I remember someone somewhere had posted about the need to dissable the back emf and/or the inertia to solve the problem. You may have to entre certain figures into thw right settings like 0 or 100 etc... I can't remember what I did but it worked. The loco has run excellently since. The decoder had given issues witth the loco when it was on its default settings but not when the back emf and inertia were dissabled. I think it was just the inertia.that needed to be turned off.

I have also heard that some have had the occasional issue with Hattons decoders, though I dont know what the issues actually were.

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SRman
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Re: Perfect on DC but not DCC

Postby SRman » Sat Apr 27, 2019 1:07 am

There are a few things you can try:

Try a different brand of decoder.

Remove any capacitors between the brush feed wires.

Try disabling the BEMF on the decoder (as suggested by Mountain), or vary the settings where BEMF kicks in or out.

On the latter item, I have three Hornby M7 0-4-4 tank locos, all using TCS DP2X-UK direct plug in decoders. Two behave perfectly, the third exhibits kangaroo behaviour in one direction only (perfect in the opposite direction). Disabling the Back EMF fixed the extreme surging, although I still don't know for sure what was causing it in the first place.

Bigmet
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Re: Perfect on DC but not DCC

Postby Bigmet » Sat Apr 27, 2019 10:26 am

smokebox wrote:I have a new Standard class 4MT (2-6-0) that runs perfectly on DC with the blank chip and it's been run in. When I plug the decoder in (Hattons 6 pin) and run on DCC, it will go in the required direction but for only about half an inch or a couple of centimeters. It will do this maybe 3 or 4 times and then give up altogether. If I unplug the controller and then start again, the same thing happens. I ordered a new decoder chip from Hattons and the same thing happens so I guess it's not the decoder. Two other locos run with no problem.

Return it for refund or replacement as a non runner on DCC, with the explanation above.

It is most probably a minor assembly or component fault somewhere in the mechanism, either momentarily interrupting power supply to the decoder, or causing very brief short circuits, which has the same effect.

(The alternative since you know the motor runs well when it gets DC supply, is to strip the loco completely, remove all superfluous components, rebuild checking the conduction paths at every step and hard wiring the decoder. Then it will run. But I suspect you wouldn't be asking the question, but would already be doing this if you were confident, making return the better option.)

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RAF96
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Re: Perfect on DC but not DCC

Postby RAF96 » Sat Apr 27, 2019 8:10 pm

Before undertaking major surgery try a different make of decoder. Certain makes are shall we say not very good.
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smokebox
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Re: Perfect on DC but not DCC

Postby smokebox » Thu May 02, 2019 5:39 am

Thank you all for your help.
I plugged in a working decoder from another loco and the same thing happened so it's not the decoder. Although I said the loco is new, I'd had it for a year before opening the box so the warranty has expired plus I live in the USA which makes returning it to the UK a bit more complicated. I'm going to take the advice of Bigmet and do a complete rebuild and install a hard wired quality decoder. If I'm modeling British steam and living over here, I think I should get used to having to do a lot of my own maintenance.

Paul-H
Posts: 208
Joined: Fri Jun 05, 2009 3:00 pm

Re: Perfect on DC but not DCC

Postby Paul-H » Fri May 03, 2019 7:41 am

Have you tried a quality decoder ie Zimo or Lenz or are you just swapping Hattons for Hattons decoders, Hattons decoders are not the best and can give quite erratic running.

Also in addition to what's been said above also turn off running on DC via CV29 some play up when that's turned on.

Mind you with is running fine in one direction, it does sound like a build issue so may warrant a total strip down, but good luck with that, assuming from the mention of a 6 pin decoder its a Farish 4mt we are talkin about :wink:

Paul


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