Sudden direction change while running.

Discussion in 'DCC & Electronics' started by Chessie1973, Jul 8, 2004.

  1. Chessie1973

    Chessie1973 Member

    I have a Stewart F7 that I have installed an MRC AD370 sound decoder in.

    It has run great now for over a month when suddenly tonight in the middle of running it suddenly acts like the direction control has been reversed.

    It was very strange. I was sitting here at my computer letting the train run slowly around my loop when it all of a sudden went from going forwards to running backwards.

    All of my other DCC equipped locomotives run correctly on the layout so it isn't a problem with the Digitrax system I have (a Zephyr). Not sure why it would suddenly reverse direction like that. And nothing I have tried has fixed it.

    I am seriously thinking about changing the NDOT bit on it to see if that helps any.

    BTW this loco came DCC ready with the NMRA plug.
  2. Gary Pfeil

    Gary Pfeil Active Member

    Hi Randall, I had a similar problem with a soundtraxx decoder. Haven't bought any of the MRC ones yet. I had installed the decoder in a brass steam loco and it operated ok for a short time, but then it would occasionally stutter, alittle while later I saw it actually go backwards, for just a second, then go back forward. Until then I had thought the stuter was a momentary short, I went crazy looking for it. Thought perhaps the brake shoes were touching a driver in a curve, etc. When it went in reverse I still thought that perhaps a short had "confused" the decoder. I eventually swapped out the decoder with a nonsound Digitrax one, and the loco ran fine, so the problem was in the decoder. You may want to try swapping the decoder with another in another loco and see if the problem moves to the new loco. I don't think the problem is going to be due to a cv setting, but I'm no expert.

    Good luck, Gary
  3. Chessie1973

    Chessie1973 Member

    Well I found the problem.

    Somehow the CV value for CV 29 got set to 49 which is a NDOT of reverse.

    I have no idea how this happened. Only thing I can figure is some sort of glitch as i set it to a value of 50 now and it works perfectly again.
  4. Gary Pfeil

    Gary Pfeil Active Member

    Randall, You're saying that the cv changed while the train was running unattended? Or when you say you were sitting at your computer do you have it interfaced with the DCC system and you were in programming on the main? Can't imagine the cv changing on its own. Unless there was a hard short which sometimes do unexpected things to decoders, I've had some locos which weren't in use start moving after a short elsewhwere on the layout.
  5. Chessie1973

    Chessie1973 Member

    I think what caused it was me running the train very slowly through these cheap Atlas #4 switches which sometimes will cause a short if the wheels hit just right.

    Sometimes my loco's will get to the switch points and stall out and the Digitrax box will indicate a short until I move the train off the switch.

    So I think what happened is the loco shorted out on the switch just enough to cause it to somehow cause the CV value for CV 29 to be changed and it just happened to change to CV 49 which is set to 28/128 speed steps and NDOT of reverse. The default should have been 38 according to the MRC decoder manual.

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