Loksound Short Circuit when Throttle is applied.

trptman Mar 4, 2019

  1. trptman

    trptman New Member

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    Strange problem - putting a Loksound Select Micro decoder into a Kato n scale MP36PH loco. The sound is working well as are the light outputs and I'm able to control these with function buttons (JMRI throttle) without difficulty. As soon as I apply some throttle, the sound ramps up, but after about 3 seconds it cuts out and my Sprog3 is flashing rapidly indicating a short-circuit. The loco never moves. The short-circuit lasts for about 1/2 second, and then 3 seconds later it does the same thing. When I place the throttle in stop, everything is fine and I'm able to reset the sound and lights.

    I thought it might be a short circuit with the motor in the loco, so I detached the gray motor lead from the loco, but this didn't change the results - still 3 seconds to a 1/2 second short-circuit etc.

    In the process of trying a few things, I accidentally touched an alligator clip to the motor solder connection where the gray wire was and bridged to the chassis - the loco lurched some, so power is going through the red wire in the decoder to the motor and back to the track on the other side. I don't think this means, anything other than the motor works, but you never know.

    I'm using DecoderPro and do not have a Lokprogrammer. This is my first attempt to do my own decoder install (my only other loco is a BLI which runs fine on this layout). I've tried DecoderPro in both Sprog and Sprog Command Station modes with no difference.

    Any debugging suggestions? Thanks!
     
  2. RBrodzinsky

    RBrodzinsky Staff Member TrainBoard Supporter

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    1) Make sure there are no solder bridges across the pads on the decoders (these do happen).
    2) disconnect both the Orange and Grey wires from the motor, and then make sure there is no short between the motor and frame (there shouldn't be or you would probably have already let the smoke out) with your multi-meter (DO NOT HAVE POWER ON)

    Your third paragraph is a bit disconcerting, since you talk about "the red wire in the decoder to the motor and back to the track". The red and black wires are picking up the track power and bringing them to the decoder, through its bridge rectifier. The decoder sends voltage to the motor via the GREY and ORANGE wires. These are not connected to the track power, but go through the motor control chips on the decoder.
     
  3. trptman

    trptman New Member

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    Rick - thank you for your reply. I misspoke above - I should have said orange wire.

    Some more info - I disconnected the orange wire, so now both orange and gray wires are disconnected. Got the same results. Then I tried putting it in reverse and applying throttle - lo and behold, it didn't short circuit! Put it in forward and applied throttle - short circuit. I then reconnected the orange and gray wires to the motor. I put it in reverse and the loco with the motor connected moved in the correct direction. Put it in forward and short circuit.

    I am suspecting a faulty decoder unless there is some CV setting that may be causing this. Has anyone seen anything like this?
     
  4. Onizukachan

    Onizukachan TrainBoard Member

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    Possible solder bridge as was stated above, as since the opposing polarity on the motor leads does not lead to short.
    But yes, it may simply be easier to exchange the decoder as defective than troubleshoot what sounds like a QA issue.
     
  5. RBrodzinsky

    RBrodzinsky Staff Member TrainBoard Supporter

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    Yep, at this point the decoder is suspect. Contact ESU, they are very good about exchanges
     

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