A question about "unknown" DCC decoders

Pastor John Mar 9, 2022

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  1. Pastor John

    Pastor John TrainBoard Member

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    I took a chance and bought a gallon ziplock bag full of DCC decoders from a batch of stuff donated to our club by a elderly former member. I paid all of $15 for five or more decoders but it remains to be seen if I can use any. All I really know about them is that they were probably purchased in the 1990's. There is no recognizable brand name on them, but they do all seem to use the standard decoder wire colors. No instructions came with any of them and the only markings are from a storefront on the west coast that no longer seems to be in business.

    I assume that when I connect them to my test track that my Digitrax throttle or my JMRI computer will be able to "read" them. But, since I've only done this a couple of times on by throttle, and not at all on my computer (yet), I don't know how much information that I will learn.

    Specifically, I have two questions.
    1) Will either of those devices tell me what brand the decoders are?
    2) Will they tell me how many functions are usable on each decoder?
     
  2. CSX Robert

    CSX Robert TrainBoard Member

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    Most if not all current decoders will give you a manufacturer code by reading CV 8, but some older ones do not support read back. Some decoders will also give you a version in CV 7. Your Digitrax throttle will not tell you the manufacturer, only the code, but JMRI will tell you the manufacturer (I believe there is an "identify decoder" function somewhere in JMRI). Note that most decoders require a motor or some other load to be able to read them. As far as the number of functions, if they are hardwired you can probably tell by the number of wires (I don't know of any that have wires for functions that aren't supported, though there could be).
     
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  3. wvgca

    wvgca TrainBoard Member

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    yes, hook up a load [motor or resistor], and just look at the wire colours for function
     
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  4. BigJake

    BigJake TrainBoard Member

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    If you wire up the decoder's DCC leads to your programming track, and motor leads to motor/resistor load, then JMRI Decoder Pro should be able to read out the decoder brand and type (series), and all register contents.

    Warning: JMRI has been found by the Surgeon General to be highly addictive. Symptoms include severe aversion to using DCC throttles for reading or programming decoders.
     
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  5. MK

    MK TrainBoard Member

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    Pastor John, take a look at the attached PDF. It might help you in ID'ing unknown decoders. I would have posted sooner but I was traveling and didn't have access to my PC.
     

    Attached Files:

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  6. Pastor John

    Pastor John TrainBoard Member

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    Thanks everyone. I got JMRI connected and running on my shop computer for the first time this weekend, then worked at isolating the motor to the locomotive that I intend to convert to DCC, and finally alligator clipped enough wires to try reading CV values. JMRI didn't want to read the manufacturer's ID at CV8 at all, and when I read CV8 from my Digitrax controller it read back a value of zero. Our of curiosity, I then tried to read the value for the "long address" and it returned "9999." It's quite curious, particularly since I have no experience at all with JMRI. So, this week I will likely try reading some values from a locomotive that already runs just to gain experience and confidence before I delve deeper into this particular problem. My guess is that, if everything is working properly, I may eventually use by Digitrax control station to (try to) change CV8 to "JMRI" (18) or something just so that the JMRI program can read it better than a value of zero.

    Again, thanks for all your help.
     
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  7. BigJake

    BigJake TrainBoard Member

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    MK,

    That pdf should be in a sticky post!

    IINM, JMRI will not give you any information about a decoder if JMRI DP does not have a definition for that decoder. Is there a way to get DP to display a generic register map (address and contents, either decoded for standard registers, or hex value for non-standard registers, for a decoder that it does not recognize?
     

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