Erratic DCC loco

I have just made my first foray into DCC, and would appreciate some advice concerning a problem loco which is behaving erratically.
Over the last few weeks I have gathered together a DCC system (a Gaugemaster Prodigy Advance 2) and a selection of DCC fitted locos. Only just got round to putting it all together today.
The OO Bachman Class 20 (with sound) behaves perfectly, controllable down to a barely visible crawl, with no glitches of any description. The sound is also great fun.
The N gauge Peco Collett goods also behaves well, with the odd hesitation (maybe my N-gauge test track needs a clean).
However, the Bachman OO gauge 4MT 2-6-0 - which works perfectly on DC control (as do both the others) - is wildly erratic on DCC. When set in motion, it jerks to full speed, stops, jerks to full speed again etc. It seems to do exactly the same, at the same speed, whether I set the speed to 1 or 28 (max), and whether it is set for forward or reverse.
Obviously, the ultimate step would be to take it back to the retailer, but that's an hour drive each way (and I only went there yesterday to buy the Class 20, dammit). Since I am a complete novice at this, I just wonder if I have overlooked something really obvious. I have checked the obvious CVs and they all seem to be set to factory defaults.
Do I have a dud?
Thanks,
David
--
David Littlewood

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David Littlewood wrote:

Some cheap decoders are cheap rubbish and best replaced with something decent. That includes the decoders some RTR makers fit to their locos from the factory, and some decoders carrying RTR makers brand names as aftermarket accessories. You need to check whether the Hornby/Bachmann decoder being sold is "cheap tat" or "really good value for money"; they do vary to a huge extent. Experts on Hornby and Bachmann offerings will be able to list which decoders fall into which category; I can only tell you that the sound ones will be excellent as they are the 100+ ESU LokSound as fitted to the 20, with different sound effects loaded.
Suggest checking that CV29 is correct, particularly the 14/28 step bit. It should be 28 step mode to match your Gaugemaster controller. It may be worth turning off DC (analogue) running in CV29 to see if that helps.

May prove to be the only thing to do. If you've been buying stuff from them, they should be able to either make it work correctly, or replace with something which works.
- Nigel
--
Nigel Cliffe,
Webmaster at http://www.2mm.org.uk/
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"David Littlewood" wrote

Have you snipped all of the (TV suppression) capacitors from around the motor? That usually solves that sort of issue.
John.
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: <snip> : : Have you snipped all of the (TV suppression) capacitors from around the : motor? That usually solves that sort of issue. :
Do DCC boards have RF interference suppression built into them?...
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"Jerry" wrote

Some do, but if they're properly designed, installation of a decoder should bypass that aspect of the circuitry.
John.
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The main source of interference from unchipped locos on a DC layout is radiation from the motor wiring and track which are connected together.
A DCC decoder isolates the motor circuit from the track so there's very little radiation of the noise due to arcing at the commutator unless the leads to the motor are excessively long.
MBQ
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wrote:

Since you put up this thread I have given myself a similar problem by simply changing chips during a test of a "failed" chip.
The combination was a chip transferred from a good loco to another good loco which then developed the stutters at slow speed. It also became reluctant to change behaviour at slow speeds in either direction until it had run for a while!
Clearly chips are motor sensitive!
In the process I found that cork underlay scrap makes excellent track cleaner.
Peter A
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"Sailor" wrote

Without knowing what chips you're referring to, it possible that the decoder has back EMF; the 'feedback' can be adjusted by changing the appropriate CV setting. It may be that your chip is back EMF sensitive rather than motor sensitive - if you followin what I mean.
If all else fails read the instructions.
John.
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Same thing. The "back EMF" comes from the motor and different motors will exhibit different characteristics.
Decoders actually measure EMF rather than back EMF but that's probably a technical detail too far.
MBQ
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wrote:

I have just received some new Bachmann decoders so we shall see!!
Peter A
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"Sailor" wrote

Oh dear; they're as bad as the Hornby ones - worse in some respects.
John.
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John, in my previous incarnation the last statement in the Emergency Operating Procedures of a Pressurised Water Reactor was that relating to a Zirconium/ Stainless steel fire -- if all else fails : piss on it!
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"Sailor" wrote

Ah well, you could always try that I suppose.
John.
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Was that a 'wont have any effect but will give some satisfaction' ?
Cheers, Simon
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A popular method for extinguishing campfires.
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Martin S.

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