First DCC Decoder install: FAILED

Discussion in 'DCC & Electronics' started by GarrettSE, Oct 15, 2010.

  1. GarrettSE

    GarrettSE TrainBoard Member

    I followed this link with the Spectrum Dash 8, right down to using the same decoder

    I did do a few things different. Instead of drilling and tapping, I drilled the holes and soldered the power and ground to the holes instead of using a screw.
    Then I sort of reused the light circuit board.
    That circuit looked like this: (the RED things are the "WIPERS" that connect on the chassis to get power and ground)


    Then I modified it to this:
    The "blue" line is the wire that the directions said was the common and the "green" lines are each bulbs power according to the directions (Obviously the colors are not exact!)

    All went well. Put it back together but didn't put the shell on, put it on the track in DC mode. It wouldn't move unless I turned the motor then it would spin a bit and then stop. The rear light worked but not the front. I got it move a short distance so I put the DCC Control to "3" and it did the same thing. Would go a short distance and then just stop. Would only go "forward." Then after a bit of fiddling it ceased to do ANYTHING. The rear light would go on when I put the controller into "Reverse" but the front light wouldn't do anything and nor did it ever.
    Even if I turned the motor a bit, it still wouldn't move. So I gave up and took the decoder out and desoldered everything and essentially gave up.

    Does anyone know what I did wrong? It would be greatly appreciated, I would like to order the same decoder and give it a shot again.
  2. AtomicVette

    AtomicVette TrainBoard Member

    are those LED's or bulbs? if they're LED's, then the way you split that circuit you've got one light hooked up with backward polarity, the front one from your description.
  3. GarrettSE

    GarrettSE TrainBoard Member

    Ya know, I didn't even think of that. It's at my buddy's house now.
    It's from 1995 so I'm not sure if that helps in deciding whether it's a LED or incandescent.
  4. CMStP&P

    CMStP&P TrainBoard Supporter

    From the pdf it looks like there are incandescent lights in this loco.

    To help you finding the error the next step would be to connect only the motor and disconnect the lights. I always do it that way.
    Then test the loco on the tracks without the lights connected.
    If the motor works than we need to look deeper into your wiring.

  5. GarrettSE

    GarrettSE TrainBoard Member

    My friend is going to build me the decoder tester at the end of the write up :D
  6. CSX Robert

    CSX Robert TrainBoard Member

    From the PDF, it does look like the lights are incandescent bulbs; however, it also looks like the light board has diodes on it to make the lighting directional, which is causing the same polarity problem as the LED's would. If this is the case, I would remove the diode for the front light, reverse it, and reinstall it. You could just place a jumper wire around that diode, but the diode will cause a voltage drop which will extend the life of the bulb.
  7. markwr

    markwr TrainBoard Member

    Try hooking up the motor and decoder with neither one installed in the locomotive. Take clip leads and attach the red and black wires to the rails and attach the orange and gray to the motor. See if the motor will run and reverse. If it doesn't, either the decoder or the motor is bad.

    If the motor runs without being installed, try installing the motor in the locomotive but still using the clip leads to connect to the rails to the red and black wires. If the motor doesn't work this way, you've probably got a problem with the motor leads touching the frame.

    Next try connecting the red and black wires to the locomotive body. You said you soldered the leads directly to the frame previously. Depending on what size soldering iron you are using you may be getting a cold solder joint. Try making the connection with the clip leads first, if this works try making the solder connection again and see if it still works.

    If everything works to this point mount the decoder to the locomotive making sure that the underside of the decoder isn't touching the frame.

    Now get the lights to work. I think CSX Robert's post explains why the lights aren't working.
  8. GarrettSE

    GarrettSE TrainBoard Member

    This is just what I am looking for, thank you! I bought another decoder and will try this when it gets here. The motor works no problem when attached to the track with wire leads in both directions.
    And I should have the decoder tester next week.
  9. lexon

    lexon TrainBoard Member

    Decoder tester

    more info
    Be advised, I found this decoder tester info on the Internet. The idea is someone elses.

    I am including some photos of my simple decoder tester. The bi-polar LED indicator works but I preferred a motor. The decoder is an older SoundTraxx LC decoder. I attach the leads from my NCE Power Cab to the two leads on the blue terminal block. The blue terminal block came form Radio Shack.

    I used a 8 pin NMRA connector mounted on standoffs on an old plastic project box. Nothing in the box except some wires to the motor.
    I removed the 120 ohm resistor, 1 k resistor and bi-polar LED. I grabbed a can motor out of an old CD burner form a cast off PC.
    I put a flywheel with diagonal black marks on the motor shaft to get an idea of decoder/motor action.
    If your decoder has the 9 pin JST connector, DCC on line companies sell a 8 pin to 9 pin adapter.
    If the decoder only has wires, I solder the wires to another 8 pin NMRA connector and plug that connector into the one on the tester.


    Last edited by a moderator: Oct 15, 2010
  10. GarrettSE

    GarrettSE TrainBoard Member

    Just out of curiosity, where in MA are you? I'm on the South Shore.
  11. lexon

    lexon TrainBoard Member


    Springfield MA area. Great train show in West Springfield every year that you must be aware of.
    I also belong to the Amherst Railway Society. They put on a fantastic two day show the end of Jan, beginning of Feb.

    Lexon is not my name but I use it for joining forums becasue rich is usually in use.

  12. GarrettSE

    GarrettSE TrainBoard Member

    Ah very nice. There any places out there to "rail fan" it? There's nothing interesting here but the MBTA.
  13. rray

    rray Staff Member TrainBoard Supporter

    You have all probably heard it many time before, but for those that have not, always check resistance between the orange and gray wires after working on a DCC loco. If you measure 0 ohms, you have a short to the motor wires, and the decoder will fry.
  14. Mike Sheridan

    Mike Sheridan TrainBoard Member

    Got to agree with that - if it's a cast frame then the chances of a good solder joint are very slim. There is a reason why the drill/tap/screw method is recommended ... and AFAIK that is pretty much it.
  15. lexon

    lexon TrainBoard Member

    I will say it again. Trying to work without a meter with DCC when doing installs can be difficult and frustrating. A couple days ago I saw that Harbor Freight has a inexpensive digital multimeter for $3.99 that does everything a DCC modeler would like. I have had three of them for some time and compare very well to my expensive meter that I hardly ever use anymore.
    I always check for continuity with the pickups and check for possible shorts. This has saved me every time from disaster and extra expense.
    The meters come with instructions and you can find all kinds of suggestions for using them on the 'Net.
    There is no excuse for not having a meter.

  16. GarrettSE

    GarrettSE TrainBoard Member

    Oh we have was just missing at the moment I needed it and I was over confident.

    Will locate for next time!
  17. Flash Blackman

    Flash Blackman Staff Member TrainBoard Supporter

    There are some really good ideas in this thread. :thumbs_up:

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