Digitrax SDN144K0a - Strange Behavior [SOLVED!]

[MetroRedLine]

I have a Digitrax SDN144K0a sound decoder installed in my Kato P42. I haven't run my P42 in several months, but now it's exhibiting some strange behavior - When I run it, the loco runs for a few feet, slows down, stops for a few seconds, then gradually speeds up to the previous speed, then repeats this behavior. I've reset the decoder and re-loaded my CV settings as stored in JMRI Decoder Pro - same thing.

I know this has NOTHING to do with track/wheel cleanliness or any sort of electrical contact, since the sound is still constant throughout (any contact issues would cut off the sound/lighting/running suddenly). I did clean the loco's wheels before running, and the track is not dirty. Also, when it slows down or speeds up, the prime mover's pitch lowers and raises accordingly, as if someone were controlling the speed manually - but no one is.

Sometimes the sound profile will act quirky - it has a custom sound profile made by a prominent Digitrax sound programmer in the DCC community, and occasionally the bell sound will get substituted for the brake squeal sounds (which gets annoying. But removing the loco from the track temporarily, or muting the sound and switching it back on will get rid of that.

Any explanations?

[Steveruger45]

Might be The locomotive cha-cha.
See this.

https://www.digitrax.com/tsd/KB175/erratic-loco-speed/

[MetroRedLine]

Might be The locomotive cha-cha.
See this.

https://www.digitrax.com/tsd/KB175/erratic-loco-speed/

I've thought about that, but I have no other throttles controlling my trains except for the one on my Digitrax DCS51.

[tehachapifan]

Does this happen after sounding the horn? I've heard of something that is called the "Digitrax stall" occurring after the horn is blown on some of the pre SDXN series decoders.

[EL3632]

I had this happen to a GP38-2, does your decoder function properly with the sound off? When I turned the sound off in mine the decoder worked as normal for me. I brought it to another layout and it worked as intended, with the sound on. I no longer own this, or any other engines with Digitrax sound, and never found a fix before I passed this one on.

[MetroRedLine]

Does this happen after sounding the horn? I've heard of something that is called the "Digitrax stall" occurring after the horn is blown on some of the pre SDXN series decoders.

I know what you're talking about, but no, this happens whether the horn is sounded or not.

[MetroRedLine]

I had this happen to a GP38-2, does your decoder function properly with the sound off? When I turned the sound off in mine the decoder worked as normal for me. I brought it to another layout and it worked as intended, with the sound on. I no longer own this, or any other engines with Digitrax sound, and never found a fix before I passed this one on.

Okay, the other peculiarity with this decoder is that the "Mute" button seems to cycle between different sound levels: Full Volume, Muted Volume (quieter) and No Sound. This didn't happen before.

[peteski]

I was going to say something about Digitrax N scale sound decoders but I better not.   Well, ok, the *ONLY* good thing about them is that they are plug-n-play install.

My opinion is based on few of my friend's locos equipped with that decoder - we both spend quite some time trying to "fix" those behaviors. 'nuff said.

[Steveruger45]

Just a thought.  Do you have any snubbers installed on the track buss?
I had some strange behavior on a couple of decoders in the past and After resetting the decoders and then installing a couple of home made snubbers, one at each end of the buss, this cured the issue of erratic decoders appearing out of nowhere.

A link and some photos attached.  NCE makes a snubber if you dont want to make your own.

https://ncedcc.zendesk.com/hc/en-us/articles/204128735-Snubber-RC-Filter

You would still need to get this particular decoder issue sorted out, but fitting these things could give you beneficial results in the future.
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Decoder appears somehow scrambled or DCC signal received erratic.
Maybe do another reset and cv reload and then also cut the power after these steps.  Sometimes the changes  don’t take unless the power is interrupted.  Sorry if you already tried that.
I would also check the decoder is not shorted or partially shorted out somewhere too.  This would disrupt a DCC signal if not completely destroy the decoder.
On these locos the wheel pick up strips need to be insulated from the motor tabs, where they fold over the pickup strips, with kapton tape.
There might be an insulation issue in this location causing the problem.  I actually redirect the motor tabs to inside to avoid them folding over the wheel pickup strips as I feel that is a safer solution by keeping the motor tabs and wheel pick ups physically separated.

Good luck.

[tehachapifan]

Though you said the horn has no effect, something I was just reading on "Digitrax stall" (can I post links here, even if it's from a dealer?) said that particular issue can be resolved by turning off BEMF. Might be worth a try anyway.

[peteski]

Though you said the horn has no effect, something I was just reading on "Digitrax stall" (can I post links here, even if it's from a dealer?) said that particular issue can be resolved by turning off BEMF. Might be worth a try anyway.

Funny how other forums make people sheepish with posting links. You should have no trouble posting any link here on TRW.  Well, excluding porn sites.    And what if someone wants to keep using BEMF?     Great workaround for a quality decoder.

BTW the horn-triggered Digitrax-stall is my friend's problem.

[conrad]

Might be The locomotive cha-cha.
See this.
https://www.digitrax.com/tsd/KB175/erratic-loco-speed/

In the same vein as what Steve suggested, are you sure you only have the loco selected on one throttle?  Perhaps you forgot to dispatch the loco some time back.  Lots of throttles (digi, etc.) allow for multiple locos.  If you're using LocoNet, I'd go to JMRI DecoderPro's LocoNet pane - Monitor Slots and clear all the slots.

Conrad

[MetroRedLine]

Though you said the horn has no effect, something I was just reading on "Digitrax stall" (can I post links here, even if it's from a dealer?) said that particular issue can be resolved by turning off BEMF. Might be worth a try anyway.

Thanks, I looked into that after reading your reply, but I already had it off ("Torque Compensation" in the JMRI profile) to begin with...And turning it on had no effect either.

[samusi01]

Have you tried doing a reset of the command station? I have a short checklist I'll occasionally do as I don't trust Digitrax slot management at all, and it's caused problems for me in the past. For some reason, clearing slots though JMRI only lasts until I power down the command station (e.g., I can clear all the slots through JMRI, shut everything down, power back up, and all the slots are still there and in use...)

My checklist:

   1. Track power off
   2. Press PROGRAM MODE, SWITCH, 3, 9, CV-WR (c(losed)), EXIT
      This resets the DCS51 to factory settings.
   3. Check command station status with either JMRI or Loconet-Checker
   4. Press PROGRAM MODE, SWITCH, 1, 8, CV-WR (c(losed)), EXIT
      This extends booster short circuit shutdown to 1/2 second.
   5. Press PROGRAM MODE, SWITCH, 2, 0, CV-WR (c(losed)), EXIT
      This disables analog stretching.
   6. Press PROGRAM MODE, SWITCH, 2, 3, CV-WR (c(losed)), EXIT
      This sets system default to 128FX mode.
   7. Press PROGRAM MODE, SWITCH, 3, 3, t/+ (t(hrown)), EXIT
      This forces system to start powered off.
   8. Press PROGRAM MODE, SWITCH, 3, 4, t/+ (t(hrown)), EXIT
      This forces system to start powered off. (Different function from 33).
   9. Check command station status with either JMRI or Loconet-Checker

[MetroRedLine]

Okay, I did some more digging into this issue. Not totally solved but I have a sense of what's going on. The loco in question has an address of 99 (It's a Kato Amtrak P42 with that road number). Apparently SOMETHING is causing my system to respond to a "phantom throttle" that is telling my system to control address 99 with alternating speed levels of 0 and the currently-set level of my throttle. When I select address 99 on my DCS51 after power on, I get a "StLo" (Steal Loco) prompt on my DCS51's display, which means the system recognizes another throttle somewhere...

I have NO external throttles, and the only thing plugged into my LocoNet jacks is one PR3 USB interface (the problem still happens if I unplug it, so that's not the cause).
In the past, I've used Engine Driver (smartphone throttle app for Android), but the last time I did that was a few years ago, and that app hasn't run since then, and I'd need to have JMRI running in the first place to use it anyway.|

For an experiment, I temporarily changed the address of loco 99 to "97." GUESS WHAT? No more problem!|

So something's giving my system a throttle command for address 99. I switched it back to 99 and the problem came back.