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Dapol Class 122 Strange Noise On DCC


richscylla
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My Dapol Class 122 was a perfect runner on DC. Then I put in a 21 pin decoder and now it has this loud noise when it runs. Does anyone know what might be causing it and if there are any remedies. 
 
For clarity....
 
Model - Dapol Class 122
Controller - Bachmann EZ Command
Chip - Zimo MX638D

 
Any help would be wonderful! Thanks. 
 
Rich
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Does it make the same noise with the body removed?

Whilst it's natural to think it's to do with the DCC decoder, perhaps you've trapped or routed a wire in such a way it's getting caught by the motor or other moving parts?

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As post 3; there is no substitute for being systematic. In principle, first find out if 'something else happened' when the decoder was installed by removing the decoder and retesting on DC. Then if it is clear that there is no mechanical cause, get to work on decoder settings.

 

(To avoid handling the model however, I would be inclined to first try a big change in decoder set up for motor drive frequency, to see if the noise can be significantly changed by the decoder: but only if I was confident that all was well mechanically, for which the indicators would be that the movement performance is as good or superior to that obtained on DC, despite the noise.)

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Sounds like the noise I had occasionally when using Digitrax chips when I first started in DCC, turned out to be the “dither” control, what I believe is called frequency adjustment on other chips, it causes the motor armature to literally stutter back and forth at high speed when at low speed settings, presumably to improve low speed performance, a lot of motors do not like it though.

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Thanks for the suggestions. I will go back and see if it's still an issue with DC operation. I'm fairly sure it made the same noise without the bodyshell and I wondered if it was BECAUSE there was no bodyshell. 

I'm very new to DCC and so if it is the frequencies that need changing I'll probably be back with hundreds more questions! 

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I do not think that the noise sounds as if there is a problem with the frequency of the decoder output.  There is none of the stutter (literal or otherwise) that this causes.  Moreover Zimo decoders offer a choice of alternative frequencies, 20kH or 40kH.  The lower of these is considerably higher than is required for any conventional motor.  It is high enough for coreless motors, with which a high frequency is essential.

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I've got a similar problem (I have a Zimo sound decoder installed).  Luckily the decoder sounds muffle the underlying noise, (but you can still hear the noise).  I have not tried running the unit on DC.  At first I thought the problem was the motor vibrating against the false floor which sits above the motor.  I ran the unit without the body and flooring installed and this seemed to improve things (but not totally eradicate the problem) .  I do not think it is a decoder problem (but am no expert), and wonder if it is something to do with the motor.  I think the noise may be amplified when the flooring and body are fitted.

 

I use a Digitrax DCC controller.             

Edited by Gopher
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The motor doesn’t get real DC, it gets a high frequency signal that is alway positive and it is this signal that you change with the various CV values.

 

Changing the motor type, chagingbthe frequenct, switching back EMF on/off, and a gust of other settings can make a terrible motor run sweetly or it can make a good model run like a dog and getting the setting right is an art not a science with what works on one loco failing to cure an other ‘identical’ loco.

Edited by WIMorrison
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  • 1 year later...

Hi Rich,

 

You might of already figured it out as I see this is an old thread, but i've been having the same issue with my Dapol 121 that i fitted with a Zimo MX634 chip today.

 

I came across your post on here long before I discovered the solution, so maybe this information will be of help to you, or anyone else with the same problem in future.

 

In essence it appears that it is the Back EMF functionality that is causing the noise, as it looks like it is set to be on max by default.

 

To adjust the Back EMF is CV 58. The default value i had is 255, which is fully on. Set this to 0 to turn the Back EMF off.

 

This should solve your noise problem - it did with mine.

 

Hope this helps.

 

CoBoLoco

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