Need help from the DCC installation gurus

Primavw Nov 16, 2012

  1. Primavw

    Primavw TrainBoard Member

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    My frustration is mounting with a Digitrax SDN144K1E. I purchased this decoder brand new last year. Upon pulling my Kato SD70M apart to install the decoder, I had terrible pick-up. Basically, the loco had to be pushed down with some force to get it to fire up, and release of pressure would cause it to shut off. I cleaned the copper "wipers", isolated the motor. This time no pressure was needed, but the loco would then start, stall and reset. So the next assumption was the decoder needed a capacitor. So I sourced a Digikey 47UF cap. I installed the thing tonight because honestly I just didn't want to tackle this until now. So the cap is installed, and I put everything back together, and suprise, suprise I have the same issue.

    Below are three videos of the behavior of the frame under power.

    1. "wipers" and frame directly on tracks, tabs from decoder to motor contacts removed, no movement from motor.
    [video=youtube;be_ewPVmeaA]http://www.youtube.com/watch?v=be_ewPVmeaA[/video]

    2. "wipers" and frame directly on track with trucks removed, tabs from decoder on, motor moving
    [video=youtube;Ns0pvS8p-I0]http://www.youtube.com/watch?v=Ns0pvS8p-I0[/video]

    3. Trucks installed, stalling, stopping, and resetting
    [video=youtube;VEn-hj3sa50]http://www.youtube.com/watch?v=VEn-hj3sa50[/video]


    Honestly, I am still a novice when it comes to DCC, and having limited experience with electrical and almost no experience with electronics, I've exhausted my knowledge and resources... is there anyone out there who would like to help me troubleshoot this loco? Possibly I could send it over to you and let you take a look at it? Honestly, without help I'm about to sell the whole thing for parts and take a loss ($70 loco, $50 decoder, $10 capacitor, $20 materials, milled frame, hole in tank...). So any help would be a big relief.

    Josh

    PS- Seems like the problem is starting at the pickup from the trucks, but there is no garauntee I installed the cap correctly...
     
  2. jp2005

    jp2005 TrainBoard Member

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    I've had the exact same problem, although with an Atlas SD50 and a SDN144A1. I've since swapped it for the non-sound version and it runs fine. Seems to be a decoder issue. When I had that decoder, it performed and acted just like yours.
     
  3. Bob Horn

    Bob Horn TrainBoard Member

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    Check your PM. Bob
     
  4. Bob Horn

    Bob Horn TrainBoard Member

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    It is not a decoder problem guys. Every one is chassis or contact issues. Bob
     
  5. Carl Sowell

    Carl Sowell TrainBoard Supporter

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    Josh, I'm no expert by any means but in looking at your last vid with the unit trying to run I think I see something that could be causing the problem. It looks like, my 72 year old eyes may be fooling me, that the pickup strip is laying to one side of the truck rab instead of on top of it. Check and make sure all four truck tabs are being contacted on top. Might be the prob. Those wipers have to go in a certain way.

    Carl
     
  6. customNscaler

    customNscaler TrainBoard Member

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    Carl is correct. The truck contacts are not doing there job, make sure the long copper strips that run along side of the chassis are secured in the chassis properly. After you do this get the fuel tank on the chassis as this helps keep the long copper strips situated in the correct form. Finally find the ends of the copper strips located at the trucks and make sure they are resting on the tab sticking up from the truck. There should be sprung like pressure from the copper strip pushing down on the truck, this would be a good time to make sure every thing is clean. Hope this helps.
     
  7. customNscaler

    customNscaler TrainBoard Member

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    Here is a picture to show you how the contacts should look, hope this helps.
     

    Attached Files:

  8. Primavw

    Primavw TrainBoard Member

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    Thanks folks, I do understand the contacts should be touching at the trucks... I'll make triple sure and report back
     
  9. ken G Price

    ken G Price TrainBoard Member

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    On my Kato's or Atlas it makes absolutely no difference if one or two of the wipers are not directly on top of the contacts.
    I will put them back on top when I do notice them off.

    You did not state if you really cleaned the wheels really good. All of the other stuff is is no use if you did not.
    Many times if my engines act as yours are doing and it is not a loose decoder board then a good wheel cleaning works wonders.

    If you have done a good wheel cleaning then, good luck otherwise.
     
  10. Primavw

    Primavw TrainBoard Member

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    Ok, so I cleaned the trucks, and wheels, and brass strips... no improvement. The only other thing I can think of is... the mechanism itself. Does anyone have a DCC SD70M (revised) with digitrax sound?

    [​IMG]

    I have two orginal SD70M's with the worm gears and different trucks. NS #2599 and #2608. #2599 has an MRC sound board, and #2608 has a digitrax non-sound board. The problem loco is #2596, a revised mech. I vaguely remember when I had this problem last year, switching the decoder into one of my other units and it working correctly. So, tomorrow, when its not so late, I'm going to swap the decoder back into one of the original units. If the darn thing works, I'm going to order a 10mm speaker and keep the decoder in my original mechs. Then I will throw one of my non-sound DCC boards in #2596 and put the damn thing on light duty.
     
  11. Avel

    Avel TrainBoard Member

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    The decoder could be loose in the frame. What I mean, the tabs on the frame halves that the decoder slides into, is it a tight fit? Can you wedge some aluminum foil between the decoder and the slot on the frame where it slides into? Or even tape so that the fit is tighter. I used solder to build up the pads on the decoder for a more secure fit. Also about the cap, I read somewhere that the new versions of the decoder where coming with 370uF capacitors. I have a Digitrax sound decoder that I replaced the stock capacitor with a 220uF. That eliminated the slowdowns when using the horn.
     
  12. Primavw

    Primavw TrainBoard Member

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    No its pretty tightly wedged in there. I used a voltmeter on the tabs from the decoder to the motor pickups and you can see the volts rise as it attempts to move, then it resets, and the volts drop to zero. This isn't so much of a "slow down" issue. Heck I'd take take over what its doing now.
     
  13. Primavw

    Primavw TrainBoard Member

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    Ok, so I swapped the decoder into one of my other SD70M's, and it is still having the problem. I also placed the DC lightboard back into #2596 and it works just fine. So I have decided it is the decoder, and not the mechanism. I plan on calling Digitrax at the beginning of the week, and if they won't repair/replace the decoder (especially since I soldered a random capacitor onto it), I guess its going back into its bag and onto a dusty shelf. Thanks everyone for the tips, but I guess I ust had a DOA decoder...

    Its just a shame that I milled out the frame and spent considerable money on trying to make it work, and it was a bit of a waste.
     
  14. mtntrainman

    mtntrainman TrainBoard Supporter

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    I been reading of lots of Digitrax decoders arriving DOA :-(
     
  15. maxairedale

    maxairedale TrainBoard Member

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    No reason to shelve the loco if Digitrax does not replace it. Just get another decoder of the brand of your choice.
     
  16. ram53

    ram53 TrainBoard Member

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    Let's assume the board sits tightly in the frame and is not loose (issues with different board thicknesses and frame slot thickness). Let's also assume you've got the pickup strips aligned properly with the truck tabs, and that the trucks are clean, wheels in gauge, etc. All that basic stuff.

    You still need more capacitance, 47 uF is not enough for a Digitrax sound decoder. I'm installing the same decoder right now in an FVM GEVO and I'm using 300uF, with 3-100 uF surface mount tantalum caps in parallel. You have to find space on the frame, usually at the back. Polarity is critical, if you accidently install it in reverse polarity, it usually is damaged and ceases to function. I have found that 100 uF is not enough, 200 uF might be enough, but 300 uF yields a engine that runs without stalls and restarts. The photo shows the 3 caps (little black rectangular shapes at the rear of the engine) using a piece of left-over LED lead to solder them all together, one piece across all three negative sides, one across the blue positive. Then attach a wire to each side and solder to the appropriate pad on the decoder. If you have to push them under the decoder because of space issues, coat the exposed metal with epoxy as shorts can occur.

    These come from DigiKey and the part number is 718-1491-1-ND Cap Tant 100uF 16V Vishay/Sprague. They are indispensible for installing Digitrax sound decoders. I don't have stalling issues with 300uF and I kind of like Digitrax's decoders now as you can download different soundfiles from either their site or the Digitraxsound Yahoo Group. The SDN144K1E has SD40-2 and GEVO files on it, but not an SD70MAC, but you can get one of those on one of the two sites I've listed, I forget offhand exactly where. You do need a PR-3 Soundloader from Digitrax to do this though.

    P1080527.JPG

    Richard.
     
  17. rrjim1

    rrjim1 TrainBoard Member

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    IMO 99% of the decoders arrives just fine, it's the installer that makes it dead. I have seen installs that look like a 5 year old did it! How many people even test a newly installed decoder before putting full power to them? My guess, not very many, they just send it back and try again!
     
  18. Rich Businger

    Rich Businger TrainBoard Member

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    Since your are new to DCC, why didn't you used the supplied capacitor from Digitrax? It is already soldered to the decoder for you. This looks like it is a power pickup problem and not the decoder. Digitrax tests every decoder before its packaged. I have witnessed them doing so. RRJIM1 is correct about installers damaging most decoders.


    Rich
     
  19. ram53

    ram53 TrainBoard Member

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    To me, it looks like a not-enough-capacitance problem. The Digitrax sound decoders will simply not work without at least 100uF, they do just what the video shows and it's extremely frustrating! You used a Digikey 47 uF Cap, you can get 100 uF ones that are physically the same size like the one I listed earlier. Or you could try parallel wiring two 47 uF caps to get 94 uF, if you have more of them, and if there is space. Make sure the blue sides (positive) are together, then use a piece of wire or LED lead to solder the + ends together, then the -, then make sure you take the wire from the positive cap pad on the decoder and solder to the + side of your two combined caps. Then the -. Use the photodiagram in the manual to be sure which lead is the positive one. You should get an improvement, maybe good enough. If it's improved but still stalls and restarts fairly often, you need more than 94 uF.

    The other problem with Digitrax's sound decoders is the sound amp hogs power from the motor control side, so using the sound functions slows the engine quite noticeably and annoyingly. This can be eliminated by disabling all BEMF CVs, 54 through 57 I think. Digitrax really does need to put some effort into fixing this quirk.
     
  20. Primavw

    Primavw TrainBoard Member

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    I have gone over all of these steps as I mentioned earlier.

    Honestly folks, I'm not sure if I have done anything to "hurt" the decoder on install... but this is a drop in decoder, so really, I bought in to the whole,"take the light board out put the decoder in, program and run the loco" idea. I have diagnosed this unit per member instructions to exhaustion. It is NOT a pick-up issue as the loco runs fine on DC with the lightboard, and with a non-sound Digitrax decoder.

    I did not install the supplied cap because the frame would have to be milled further to fit it since its rather large. It is NOT soldered to the board at time of purchase, and Digitrax calls it a "suggested" step. I am not interested in installed 2 more caps because I have already spent a decent amount of money to make it work, and I'm not willing to go through the effort and have it not fix the issue, or risk damaging the decoder past what Digitrax will will cover. I am going to talk to Digitrax and see what they suggest. If anything I will pay to send it over to them and have it diagnosed/installed.

    I have other Digitrax decoders in my SD70M and an Atlas high nose and they literally took 5 mins to install, and ran great. I have not lost faith in Digitrax, but reading reviews and complaints wider than in this forum alone, I have figured this particular decoder has had problems and the likelihood of it being the issue is what I'm banking on.
     

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