Loco Unresponsive After Starting Up - Works with

[StuB80]

Hi, I'm new to the forum and DCC layouts but am really hoping that someone can help with an issue on a new layout that I'm struggling to get my head around - apologies in advance for the long post, I'm just trying to share as much info as possible!

I'm building a new dual oval layout with a handful of sidings, approx 1.8m x 2.4m with a 32/0.2 DCC bus and 16/0.2 dropper wires fixed to the track in multiple areas, all controlled by a Hornby Elite.  At the moment I only have one DCC fitted train - from a hornby R1230 class 43 hst set that I have fitted with R8120 sound enabled decoder.

If the train is stationary, then all sounds work perfectly fine and the train will start to move in the right direction when the controller is operated. Unfortunately this is where the expected behaviour ends! As soon as the train is in motion it won't respond to any commands (movement and sound) from the controller and can only be stopped by the emergency button. When the emergency button is reset the train will then respond again until it is in motion once more.

I have tried numerous things to rule out various items (including a second DCC decoder) and have reached a point where I can now replicate the issue away from the layout with a few pieces of straight track connected together with some short dropper wires soldered to one end that are connected straight into the controller. 

I have also found a configuration that resolves the issue but goes against the guidance I had read up on when planning and putting the layout together!  If I place a track connector (i.e. one of the black ones supplied in the R8201 DC link wire) with no input wires in it, at any point of the track the train responds perfectly when in motion and responds to motion/sound instructions as expected.  I'm guessing the component that is contained within the clip is having some form of positive effect on the circuit, so with this I have tried creating a 'bus terminator' as per the suggestion on the Brian Lambert guide but this made no difference. 

As that was the last idea I had I'm hoping someone can offer some advice, I don't really want to leave a track connector in the layout just for the sake of it but guess I could detach the component in it and solder it into the circuit out of sight if it resolves the problem, but equally it seems to go against everything I've read and I don't want to create problems further down the line.

Thanks in advance!

[Chrissaf]

....apologies in advance for the long post, I'm just trying to share as much info as possible!

 

Apologies not needed. Your post is perfect. Huge amounts of detail in a well constructed logical concise set of paragraphs, detailing the issue and what you have done so far to resolve it.

 

Something we see far too little off.

 

If I place a track connector (i.e. one of the black ones supplied in the R8201 DC link wire) with no input wires in it, at any point of the track the train responds perfectly when in motion and responds to motion/sound instructions as expected.

 

This is extremely odd and completely unexpected. The R8201 is a DC Analogue product and contains a 0.1µF suppression capacitor in it, that in essence goes across the two rails. Now what makes this very odd indeed, is that in every other documented case, this suppression capacitor has detrimental effects on the DCC signal, not positive ones. And has the complete opposite effect of what you are observing.

 

The only thing I can suggest is that you use the Elite to read the value of CV29. If you read a value of 6, then write a value of 2 to it instead. If you don't read a value of 6 and it isn't already 2 then tell us what value you do get and await further advice.

 

A value of 2 will disable 'DC Operation' and may possibly help with the following symptom you described:

 

As soon as the train is in motion it won't respond to any commands (movement and sound) from the controller and can only be stopped by the emergency button.

 

To be honest, the symptom described above in the quote of your post is exactly what one might expect to see when the suppression capacitor is present, not removed.

 

If adjusting CV29 as described makes no improvement, then I would try swapping the two decoders round, so the dummy car decoder is in the motor car and the motor car decoder is in the dummy car and see what happens.

 

If still no improvement, write 8 to CV8 to perform a factory reset on both decoders and start configuring them again. Making sure to check CV29 again and make it 2 if it isn't already.

 

If still no improvement, then in the absence of anybody else on the forum offering alternative advice, I suggest you treat the R8120 dual decoder pack as potentially faulty and negotiate a replacement from your supplier.

 

To the best of my recollection, I do seem to vaguely recall Class 43 HST R8120 decoders being reported before with similar symptoms. In those cases, they were returned for refund/replacement. Refund and purchasing again from a different supplier might be the more prudent option to undertake, as your original supplier might have a bad batch and any replacement that supplier provides potentially might have the same issue.

 

TIP: As a newbie poster on the forum, just be aware that the 'Blue Button with the White Arrow' is not a 'Reply to this post' button. If you want to reply to any of the posts, scroll down and write your reply in the reply text box at the bottom of the page and click the Green 'Reply' button.

 

See also – further TIPs on how to get the best user experience from this forum.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

 

[Fishmanoz]

Hi Stu, welcome to the forums and thank you for a very informative first post where you have given a lot of relevant information to us to help solve your problem. 

As you have rightly surmised, your "fix" is completely counter-intuitive because the capacitor connected across the track by that connector should make things worse as its effect should be to distort the DCC signal (the capacitor presents a lower and lower resistance to higher and higher frequency components in the signal, effectively shorting them out).

 

However, in your case, the "undistorted" signal is not being properly recognised by the decoder whereas the "distorted" is.  That, combined with the fact that your Elite is the common factor in what you've tried, suggests to me the possibility that your Elite is producing a distorted output (ringing on the DCC) which that capacitor is then correcting.

 

Therefore I'm thinking return the Elite to Hornby for testing.

 

But I'm also interested to hear what others think of your problem and my suggested solution. 

Just one question - does the connector fix the issue on your short test track too?

PS.  Chris has posted while I was typing.  I had discounted the decoder as Stu told us he had tried another. But if that was a second from a dual pack, Chris may be correct. 

 

[Chrissaf]

Fishy,

He did say [see quote below] that he tried the terminator documented on Brian Lambert's site. I assume that was a capacitor / resistor 'snubber' circuit. In theory, that should limit any ringing that the Elite might possibly be producing.

 

I have tried creating a 'bus terminator' as per the suggestion on the Brian Lambert guide but this made no difference.

[Fishmanoz]

I noted that Chris, I was thinking it to be a possible solution until I saw it.  And yes, you could be right that the snubber should stop any ringing in the original DCC signal. Yet what Stu is reporting says not so.  He is reporting more extreme damping than a snubber is needed to "correct" the DCC. Again says to me the signal was wrong in the first place. 

[Chrissaf]

I do agree that the Elite cannot be fully discounted at this stage. It really needs another loco exhibiting the same symptoms or not as the case may be to re-enforce or eliminate the Elite as a possible cause.

[StuB80]

Thanks for the warm welcome and the replies so far, it's much appreciated! 

 

I've checked CV29 and the value was 1 but I tried setting it to 2 which made no difference so for now I have put it back as assuming I have it right, I set this as part of the initial configuration to alter the direction.  I have tried the CV8 reset previously which didn't make a difference.  The decoders did indeed come as a pair and I haven't done much more with the second decoder beyond plugging it in and assigning a new id to it - the dummy car is essentially just a shell with no circuitry at all so I had planned to sell it on. I will take another look later though just to be sure.

 

I did wonder about the Elite as its a difficult one to rule out and I bought it second hand. It was sold as working but understandably that may not have been the case.  There is a faint buzzing sound emitted from it when it is on but I did some research on that and discounted it as it was suggested that was normal (you only notice it if it is within a few cms of earshot).  I did also upgrade the firmware to v1.44 and performed a factory reset on it before I started using it too.

 

I do also have a DCC ready Tornado that I might upgrade to DCC sooner than I'd planned, it would at least give me more options on the locos/chips as well.

 

Thanks for the suggestions so far, I'll add updates as I go! :-)

 

Stu

[Chrissaf]

I've checked CV29 and the value was 1 but I tried setting it to 2 which made no difference so for now I have put it back as assuming I have it right, I set this as part of the initial configuration to alter the direction.

 

Based upon the information in the quote above I strongly suggest that the optimum value that you set in CV29 is a value of 3. This may not resolve your issue, but the corrected value will help to ready your loco for when the issue is resolved.

 

The 1 is for reversing the direction.

The 2 is for 128 speed steps which is pretty much the default required now for correct decoder operation with modern DCC controllers.

 

1 plus 2 = 3

[Fishmanoz]

Changing CV29 from 1 to 2 should make a difference as Chris says. Did you check if it reversed the direction of the loco v what the controller is saying.

 

I would definitely not leave as 1.  Like Chris says, 2 for 128 speed steps, 3 if reversed direction needed.  Or if you want to run on DC (usually not recommended), then 6 or 7.

[StuB80]

So I've managed to get my hands on two more dcc chips; one that I have fitted to an 0-4-0 saddle tank engine and a R8108 TTS decoder that i have fitted to my DCC ready Tornado, and I now feel more even more confused about this issue than ever! 

 

Whilst the behaviour of the HST (CV29 value 3) is no different and works perfectly with the power connector in the track, the other two are showing completely different symptoms that do not change irrespective of whether the power connector is present. 

 

The sound on the Tornado works perfectly but when starting the motion, the wheels turn approximately 1/4 way round and then the loco stops completely. CV29 value is 3.

 

The 0-4-0 fairs a little better in that it moves further and stops when instructed around 60% of the but there are still occasions where it doesn't stop or stalls abruptly. CV29 value is 2.

 

This behaviour is consistent on both my main oval layout and the short test straight that I have constructed. 

 

All 3 locos work fine under a DC setup with the chips removed.

 

I'm open to suggestions if anyone has any other ideas but the only thing that I haven't ruled out now is the Elite controller so I think I'll try and see if a local retailer can help test it further when lockdown is over. 

 

I'm also going to invest in some track cleaning tools in case the track/wheels are dirty but they look ok and the HST and track are brand new.