Loco won't run with DCC - DC OK

[craigwatkinson]

Hello,

 

I have a loco that came DCC fitted which refuses to run under DCC. If I remove the 21-pin decoder and fit a blanking plate, it runs correctly on DC. I have bought a new decoder and tried that, same behaviour, so the obvious answer of a faulty decoder appears not to be the case. The controller (Hornby Select) runs other DCC locos with no issues. All wires within the loco appear to be connected, and have not come loose. I have tried re-programming the loco address back to 3. 

 

 

Any suggestions on how to proceed would be much appreciated. I'm a bit stuck.

 

Thanks

[johnd]

To reset the decoder to its original setting have you tried programming it  CV8 to 8 ? and see what happens its resets  the loco address to 3.

Edited April 4, 2021 by johnd

[craigwatkinson]

I have not tried that, but the new decoder would presumably come with default settings? I'll give it a go though.

 

The other thought I had since writing the post was that the original decoder might be programmed with a 4 digit code. I don't think the Select controller correctly re-writes these as it doesn't support 4 digit codes, but again, that wouldn't apply to the new decoder.

 

Cheers

[Kaput]

2 Important questions.

 

Which loco and which decoder(s)?

[craigwatkinson]

Hello,

 

The loco is a Bachmann Windhoff MPV, 32-576DC. I presume the controller is the one supplied by Bachmann, but I don't know for certain. Pictures below incase it looks familiar to anybody.

The other controller I tried was a Rails Connect decoder, again, pic below.

Cheers Craig

[Kaput]

Ah, the MPV has a history of being tempramental with decoders. When I had one a while back it would only work with a Hornby Sapphire decoder.

 

The factory fitted one is possibly one of the old rebadged ESU LokPilot Basic's.

 

As the Sapphire is nearly impossible to get these days I'd try a Zimo MX633D in it.

[John ks]

If it was mine i would remove the 3 capacitors on the motor, they are there for RFI suppression 

 

I've got a HST that would run erratically when i installed a Hornby TTS sound decoder Running on Digitrax 

When i removed the RFI capacitors it ran fine

 

On the mother board are 2 components which i am fairly sure are Inductors (marked J1 & J2) & would also be part of the RFI suppression & i suspect that capacitors C3 & C4 are also RFI suppression

If I had one of these locos then i could trace the motor circuit & would know if J1, J2, C3 & C4 were RFI components & could be removed

If J1 & J2 are inductors & were removed then they would have to be replaced with jumpers

John

 

 

 

 

Edited April 5, 2021 by John ks
added image

[KingEdwardII]

Hmm, the components labelled as "Inductors" on the picture in the previous post look awfully like resistors - they even have the resistor colour coded markings on them. I would not recommend removing those resistors.

 

Yours, Mike.

[WIMorrison]

If a loco is supplied DCC Ready with a socket then you do not need to remove the DC RF suppression circuit components (capacitor and coil) because they are not in the circuit when a decoder is fitted.

 

they are only in circuit when the blanking plug is fitted.

[Nigelcliffe]

20 minutes ago, KingEdwardII said:

Hmm, the components labelled as "Inductors" on the picture in the previous post look awfully like resistors - they even have the resistor colour coded markings on them. I would not recommend removing those resistors.

 

Yours, Mike.

 

Inductors also have colour codes, with bands around them.   They look more like inductors than resistors to me, and the colour codes make sense as an inductor.  

 

 

6 minutes ago, WIMorrison said:

If a loco is supplied DCC Ready with a socket then you do not need to remove the DC RF suppression circuit components (capacitor and coil) because they are not in the circuit when a decoder is fitted.

 

they are only in circuit when the blanking plug is fitted.

 

Not in most (all) locos.   In most locos the suppression components have to be "in circuit" because the blanking plug is just some wires to link "pickup" to "motor" with a wire link.   The decoder does the same, but via the decoder's internal circuitry to decode the DCC signal and create motor voltages.  There is no connection which allows "suppression but only if blanking plate" unless the suppression components were placed on the blanking plate (which is not the case).  

 

 

 

[Crosland]

As Nigel says, and...

 

If you want to remove ALL of the suppression components then the inductors need to be replaced by wire links (that may be why they are labelled J, for Jumper) as they will be in series with the motor. The capacitors can just be removed.

[craigwatkinson]

Hi all,

 

thanks for the suggestions so far. My main question is why it should be necessary to remove the suppression components? The loco was supplied as DCC fitted by Bachmann, and hence I would expect it to work as intended. If it had been converted to DCC by somebody who didn't quite get it correct, then this may be necessary, but that is not the case.

 

Please can somebody explain the reasoning behind this, and why it might help?

 

Thanks

Craig

[WIMorrison]

Craig

 

you are absolutely correct, you shouldn’t need to remove any components 

[Nigelcliffe]

Multiple different things in the thread...

 

Loco not running at all on DCC, yet runs on DC with blanking plate, with multiple decoders, which (presumably) work in other locos.   Then the problem has to be something about the loco causes the decoder to not function.   

 

Yes, ideally the loco should just work.  

 

1 - might be the DCC system.  The Select isn't that highly thought of, and in its earliest form wasn't really DCC-compliant (see German model rail press early reviews).   So it might be the Select.  But as the decoders work in other locos that doesn't seem a high probability. 

 

2 - if loco is newly purchased, return to seller as "not working on DCC".   If you've owned it a while, from new, talk to either retailer or manufacturer about it and a warranty issue.  

 

3 - change settings in the decoder.  It may the motor sensing back-emf stuff causing the issue (caused by the capacitors/inductors around the motor in the model), so change the settings in decoder to turn off back-emf sensing.  Different CV changes in each decoder, and needs decoder manual.   

This is also why the comments about installing certain decoders which have reputations of being more capable in these situations.  

 

4 - alter the loco so decoder may work.  Many suppression components make it hard for decoders to measure back-EMF from a motor, so they can't control a motor, or the control is poor.  So the answer is remove them - they do nothing for electrical noise when a decoder is fitted (the decoder isolates the electrical noise from a motor from getting out to the rails).  

 

 

- Nigel

[craigwatkinson]

Thanks all for the suggestions, and the explanations. It's useful to know why removing the suppression components was suggested, but I think it's my last port of call. I'm ultimately looking to ensure this model is working correctly prior to selling it, and if I can't get it to work with DCC, then I will need the caps/inductors if it is to be any use as a DC only model.

 

I have the received the Zimo decoder that I ordered off the back of @Kaput's advice, and will try resetting the existing decoder, as well as digging out my Elite controller. I have some time today to try this. I'll let you know how I get on.

 

Cheers Craig

[craigwatkinson]

Hello,

 

thanks again for the suggestions - short update. 

 

- trying an Elite controller didn't make any difference

- re-programming address from the Elite didn't make any difference

- resetting the supplied decoder to default settings didn't make any difference

- replacing the supplied decoder with the recommended Zimo decoder  - worked - \o/

 

So not ideal that I have had to replace the existing controller, and doubly not ideal that the Rails decoder I bought didn't work, but great that it is working as it should, and I can now sell it as a working model.

 

Thanks again for all the help and suggestions

 

Craig