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Author Topic: Strange issues with Zimo MX621N decoders & Z21 double heading  (Read 200 times)

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Offline jpendle

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Hi,

I use a Z21 and 90% of my locos have Zimo decoders, MX621N, MX622N, MX617N, & MX618N18.

I have been experimenting with the Z21's "Multi-traction" feature, which allows the creation of 'trains' for double heading and banking. Each loco has a set of measured traction setting times stored on the Z21 app and then a 'train' can be created with 2 or more locos from the Z21 database.

I have setup 2 CL68's to top and tail a nuclear flask train and that works reasonably well.

I have also tried to setup 2 CL86's to double head an intermodal train and that is where my problems began.

One loco has an MX617N fitted and the other has an MX621N. I presumed that this would not be an issue and went about timing each loco at various speed steps over a fixed length of track to get the traction settings needed to create the double header 'train'.

The loco with the MX621N was over 3 times slower than the other at virtually every speed step setting I tried. For example at SS40, the MX612N fitted loco would take 90 seconds to traverse my storage yards, the other loco only took 30 seconds at SS40.

I tried to setup a 'train' but found that the locos would stop and start at fixed intervals around my layout, which I assumed was caused by the vastly different speed performance of the locos.

I decided to investigate and ran a number of experiments.

I ran both locos on my DC test track, with the decoders still fitted, and measured track voltage and current draw. Both loco's draw around 110mA and run at roughly the same speed, at any voltage between 6V and 12V. One issue I found was that the locos would run in opposite directions when placed on the DC test track at the same time.

Next I decided to check CV settings, although both decoders were bought brand new and the only programming I have done is to change their addresses.

This is where the fun started.

The Z21 app has a feature called 'read traction settings' in CV programming mode, this reads back CV's 2 through 6. On the MX617N equipped loco I read back the Zimo default values, 1,2,1,1,1, on the MX621N equipped loco the Z21 hung up. I found that I cannot get thos to work on either of the MX621N's that I have tried but it works fine on the MX617N's and MX618N18's, maybe software revision related? When I manually read back the same CV's I got the same values on both decoders.

Next I read back CV29. On the MX617N I got a value of 14, which is the default. On the MX621N I got a value of 223!! Or 1101 1111. So my MX621N had been programmed to reverse the direction of travel, and to use the 28 step custom speed table and long addressing?, plus bits 6 & 7 were set and I have no clue what they do.
The other weird coincidence is that I had also read back CV250 to determine exactly what kind of Zimo decoder was in the loco and the value for an MX621N is also 223!

The thing I don't understand here is that the decoder was supposed to be new, and it arrived stuck in a box like all the others I have bought (I think). But somehow CV29 had been changed from the default value of 14.

Anyway I did a hard (Zimo) reset on the decoder (CV8 to zero), and read back CV29 and got a value of 14. I then checked the locos performance and it was much faster than it had been, but still wasn't as fast as the MX617N equipped loco.

I then manually checked each CV from CV1 to CV120 (I got bored) and found that both decoders had exactly the same CV settings. I swapped the decoders round and the slow performance stayed with the MX621N decoder, regardless of which CL86 it was in.

I then decided to find another MX621N equipped loco with the idea having identical MX621N decoders in my CL86's for the double header and putting the MX617N in some other 'random' loco.

I tried a couple of locos, but they both had MX622N's fitted and CV29 was set to 14 on both of those, but the third loco I tried had an MX621N. I read back CV29 and it also has a value of 223!!! So another 'new' decoder that had incorrect values in CV29. I then randomly checked 2 or 3 more locos with Next18 and MX617N decoders and they all read back 14 from CV29. I tried this 2nd MX621N in one of the CL86's and, sure enough, it ran extremely slowly, as had the first MX621N that I had tried.

OK so if you got this far here are my questions.

How can 'new' MX621N decoders have a value of 223 in CV29? Did this used to be the default value and they are just old decoders, or does it mean that they have been programmed by someone.

Why would anyone program CV29 to 223, what do bits 6 & 7 even do? I could understand programming CV29 to 31, but 223?

Why is it that an MX617N equipped loco and an MX621N equipped loco run at different speeds when the decoders are programmed the same and they are running at the same speed step settings? As I think I said, I can swap decoders around and the slow loco is always the one with the MX621N fitted. Clearly with CV29 set to use the 28 step speed table then the loco will behave very differently from one which uses the 3 step speed settings but when they are both set to 3 speed steps there is still a significant difference.

Is it foolish to assume that different Zimo decoders would behave the same as long as the loco's drive mechanisms are similar? For example I have been assuming that a Farish CL66 with either an MX617N, MX612N, or MX622N would all behave the same if the decoders had identical CV settings.

Here's hoping someone can shed a bit of light on this dark DCC hole  ;D

Thanks,

John P
« Last Edit: March 03, 2020, 09:36:50 AM by Railwaygun, Reason: Title expanded »
Check out my layout thread.

Contemporary NW (Wigan Wallgate and North Western)

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=39501.msg476247#msg476247

Offline Graham

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Re: Strange issues with Zimo MX621N decoders & Z21 double heading
« Reply #1 on: March 26, 2020, 04:36:46 AM »
Hi John ( @jpendle  )

I have just completed a test run of 2 Farish 66's, i tried to upload the video to demonstrate this but failed in the attempt.

66952 is fitted with a MX622 and 66610 is fitted with a MX617, both ran along my test track in sync. The test track has a Digikeijs 5000 to control it and i had my Digitrax throttle plugged into it. I used this to perform the consist. The CV's for both units are identical as follows:

CV 2 = 5
CV 3 = 2
CV 4 = 1
CV 5 = 255
CV 6 = 133
CV 9 = 95
CV 19 = 46

I also had similar problems with my Dapol 68's using the Imperium decoders, but when i switched to Zimo all came good.

If i get time i will see if i can get a couple of Dapol 66's set up with a 622 & 617 and see what happens, cant help on the 87's unfortunately as i dont have any.

cheers
Graham

Offline jpendle

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Re: Strange issues with Zimo MX621N decoders & Z21 double heading
« Reply #2 on: March 26, 2020, 02:11:26 PM »
Thanks very much @Graham

One reply on 3 forums after 3 weeks might be a record  :D

Anyhow, one question, is CV9 really set to 95 or is that a typo (mine are all defaulted to 55)?

I haven't actually tried creating a consist using CV19, the Z21 app allows consisting without programming CV's, so I might try that to see if that makes any difference.

Also do your two locos run at the same speed when they are NOT in a consist?

At the moment I've switched decoders so that both 86's have MX621N's and everything works fine, but I'm very tempted to invest in decoder tester so that I can do some more detailed measurements of motor voltage to try to get to the bottom of this. I'd have been really  :censored: if this had happened on locos with soldered decoders.

I'm also tempted to update the MX622's to the same software revision as the MX617N's and see what that does.

Regards,

John P

Check out my layout thread.

Contemporary NW (Wigan Wallgate and North Western)

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=39501.msg476247#msg476247

Offline Graham

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Re: Strange issues with Zimo MX621N decoders & Z21 double heading
« Reply #3 on: March 26, 2020, 09:41:44 PM »
Hi John,
I must admit to reading it on 2 forums and thinking "I am sure i have a combination which i could try this on" a couple of weeks ago, but as i mentioned only got round to it yesterday. I find it easy to put thing off till tomorrow since i retired and have no deadlines.

Both locos were running at the same speed before consist
CV9 to 95 is recommended in the fine tuning section of the Zimo manual along with CV56 to 55. I used to have both to 55 before reading this section and then made the change, it appears to me as if the slow speed running is better at 95 than it was at 55.

I have never tried to update the s/w on a decoder so will be interested in how you progress on that front.

Love your progress on Wigan, i still considering rebuilding my layout as I have to duck under and i can see this being an issue in the coming years.
cheers
Graham

Offline jpendle

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Re: Strange issues with Zimo MX621N decoders & Z21 double heading
« Reply #4 on: March 27, 2020, 01:50:47 PM »
Thanks once again.

As you know I'm, busy getting the station redone, but what with the lockdown over here as well, I'm sure I'll revisit this sooner rather than later.

Regards,

John P
Check out my layout thread.

Contemporary NW (Wigan Wallgate and North Western)

https://www.ngaugeforum.co.uk/SMFN/index.php?topic=39501.msg476247#msg476247

 

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