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Author Topic: DCC Control  (Read 4922 times)

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« on: April 29, 2011, 07:51:48 AM »

I have a Thomas Loco which after programming refuses to reverse.  Has anybody got any ideas as how I can resolve this?
Jim Banner

Enjoying electric model railroading since 1950.

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« Reply #1 on: April 29, 2011, 01:09:08 PM »

It is impossible to make any kind of guess with so little information to go on.  Perhaps you could tell us:
- what locomotive we are discussing and who it was made by.
- what decoder is installed.
- who installed the decoder - the factory, you, or a third party.
- if you or a third party installed the decoder, how the locomotive ran on dc before the installation.
- if you installed the decoder, what was the motor stall current at 12 volts?  How did this compare to the decoder rating?
- what DCC system you programmed the decoder with and how successfully it programmed other decoders.
- what DCC system you tried to run it with and how other locomotives run with it.
- whether or not it ran properly both forward and reverse when you tried it on address 3 before programming it.
- whether you reset the decoder and tried programming it again.
- whether you tried a different decoder.


Growing older is mandatory but growing up is optional.

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« Reply #2 on: April 29, 2011, 02:35:05 PM »

1. The loco is a Thomas made by Hornby
2. The decoder is an R8249 4 function
3. It was installed by my local model shop
4. Not tried prior to installation
5. ?
6. I am using the Bachman Dynamis system
7. It ran O.K in the shop before I brought it home (they were using Hornby DCC Controller)
8. All other loco's run very well, no problems.
9. No it only ran forwards
10. Yes I did reset it and no it still only runs forwards
11. No, but I did return it and there comment was "reverse was switched off"Huh? but the problem still persists

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« Reply #3 on: April 29, 2011, 08:37:37 PM »

Reverse was switched off? I've never heard of a CV setting that can do that. Has anyone else? What would be the point of it?
Can you reverse your other locos? Did you enter 8 into CV8 when resetting the decoder? Have you tried new batteries in the Dynamis.
If the answer to those questions is yes, then take the model back to the shop and ask them what they mean by 'reverse was switched off' and what CV setting would do that?
Jim Banner

Enjoying electric model railroading since 1950.

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« Reply #4 on: April 29, 2011, 10:06:56 PM »

Interesting comment "reverse was switched off."  I have never seen or heard of a DCC decoder where it was possible to disable reverse running and Honby's pamphlet on this decoder makes no mention of such.  I have read some reports of problems operating Hornby decoders with the Dynamis such as:

Then again, other reports have indicated specific R8249 decoders have worked properly with Dynamis such as this thread:

These problems are in spite of both Dynamis and the decoders being NMRA compliant.  No mention is made of the qualifications of the the installers and programmers.  The R8249 is a bare decoder (no insulating sleeve) and comes with the warning "To prevent the risk of electro-static damage occurring to the decoder, NEVER directly touch the component parts of a decoder PCB."  As avoiding touching the PCB (Printed Circuit Board) is well nigh impossible and very few if any decoders are installed at static free work stations, I have to wonder how many of the complaints seen online are the result of damage during installation.  I also wonder if the installer at your local model shop took all required precautions when installing this decoder.  I would guess that if he installs only Hornby decoders, he probably did.  But if he installs a wide variety of decoders, there is a good chance he did not.

There are some other possible causes of your problem.  The R8249 is a small, light duty decoder rated at 500 milliamps total for motor and accessories.  It is just possible that your locomotive draws a bit more current in reverse than in forward, either because of slightly different mechanical loads on the motor depending on direction or because the rear light draws more current than the headlight, or both.  This by itself would not explain why it runs in reverse on the Hornby system but not the Dynamis.  But adding this would:  The Dynamis may deliver a higher voltage to the track than the Hornby system.  This can be the case even if both systems are NMRA compliant.  The higher voltage could cause the current to exceed the allowable maximum in reverse, shutting down the decoder with the Dynamis.  If the Hornby system has a slightly lower track voltage, it might not send the decoder into overload in reverse.  This, by the way, is the significance of the stalled motor current tests (item 5.)

So what is the solution?  My own solution would be to replace your decoder with a more robust one.  I happen to like Digitrax decoders and would want to use a DZ125 which has only 2 function outputs (normally head and rear lights) but has a current rating of 1.0 amps.  It is also similar in size to the R8249 so I would have some assurance that it would fit.  I would not charge you for the decoder or for the installation but I would keep the R8249.  If the R8249 tested satisfactory on my decoder tester, I would consider selling it as a used decoder.  If not, I would cut it in half and toss it out.  The second decoder and installation would eat up the profit from the first one but I would have a happy customer who I could expect to return in the future rather than an unhappy ex-customer who would be bad mouthing me to all his friends.  The installer at your local model shop may see things differently.

If you like, please feel free to print out my response and take it along with you when you return to the model shop once again.

James Banner
Electronics Technologist

Growing older is mandatory but growing up is optional.

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« Reply #5 on: April 30, 2011, 04:32:42 PM »

Hi, I'm curious about a couple things,

Did it run correctly at the hobby shop when you took it back to them?

if not and they say it was "turned off"... why didn't they "turn it on" for you?

if they installed everything did you buy everything from them?

If so it seems like it should be under warranty. Programming a decoder that  wont then reset should not void it. 

If they wont get the loco up and running for you, can you please post the name of the hobby shop so others can avoid it.


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« Reply #6 on: May 31, 2011, 11:01:40 AM »

Have at last pinned down the problem - the Dynamis hand controller lost its brains for a while, but after a few attempts at re-setting it eventually corrected itself, so all's well that ends well.

Many thanks to Jim Banner, Poliss and NarrowMinded for your input and encouragement.

Best regards

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