Boy! Do I have one for you.......

HOexplorer Jan 12, 2013

  1. lexon

    lexon TrainBoard Member

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    The DCC signal comes in the connector at the bottom right in the photo. Remember the board is upside down right now.
    The signal for both sides flow up to the two black spots in the middle of the board. Two thin traces rout the power to the LED and resistor.
    On the opposite site of the PC board, two traces from those same two black circles connect to the track connector.
    I doubt another close up photo would show exactly what I am seeing.
    If the LED is on and no track power, there is at least one trace break between the two spots in the center and the track connector.
    The two spots in the center are plated through the PC board to the top side and go to the track connector. This would tell me one or both plated though holes have a break. Something I have seen over the many years of PC board work. That can be a tough one to find.
     
  2. lexon

    lexon TrainBoard Member

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    The DC power has its own to traces which sends DC power up to the cab.
    There are four other plated through holes for the DCC path that may have a crack.
    I have not figured out what the other two traces do but not important now. They may be part of the DC path.

    Rich
     
    Last edited by a moderator: Jan 18, 2013
  3. ScaleCraft

    ScaleCraft TrainBoard Member

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    True, not important, but, the LED comes from the last board through holes (circled) before the plug to the track. No power at the through holes, yet the LED lights.
    I've traced it, both sides, and there is no way for the LED to light AND the circled through holes to be dead at the same time, unless loading the circled through holes kills a bad solder joint and the LED goes out, too.
    Dave
     
  4. HOexplorer

    HOexplorer TrainBoard Supporter

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    A friend of mine came over and traced power to the large black diode just before the 'power to the tracks' needles. Power got to the diode not throught it. What I need to know from all you folks is: Could I have done something on the layout, short, reversed wiring etc., that could have made this diode not work? It worked at NCE, but not when hooked to my layout and it doesn't work sitting on the floor not hooked up to the layout? Thanks, Jim

    The diode is the one the screw drive is pointing to.

    [​IMG]
     
  5. lexon

    lexon TrainBoard Member

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    Ok, I now see why we were not in agreement. I have a different PC board. I did not see your complete PC board in your first message. Mine is NCE 2005 version. No diode on mine.


    [​IMG]

    Rich

    Rich
     
  6. ScaleCraft

    ScaleCraft TrainBoard Member

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    Now we're getting somewhere!
    You DO have power at the circled points Lexon posted.......even with the "diode".
    Since the output is DCC AC, a "diode" would shunt half the signal.
    Are we certain it's a diode? I don't see a band on the end.
    The green you see on the tracks is a lacquer coating. You cannot read voltage through it. Needs to be carefully scraped off to measure.
    Scrape both tracks next to the plug that goes to the track. Tell us if you have power on the legs of the "diode", and if you have power at the scraped portion of the tracks right next to the plug for track power.
    Dave
     
  7. lexon

    lexon TrainBoard Member

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    I just downloaded the photo and enlarged it. That does not look like a diode. I do not see any indication of the band that marks one end. There is a component ID on it but I cannot quite read it. I suspect a device to keep the DCC signal from going too high but that is just a WAG.
    The PC layout looks identical, otherwise.

    I would use the meter on AC with a loco on the track for a load and troubleshoot like looking for a bad connection on the layout. Same principle. Two paths to check.

    Rich
     
  8. ScaleCraft

    ScaleCraft TrainBoard Member

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    And the issue is the device is across the leads, not in parallel. If it was open, no problem. If it was shorted, the system would shut down and no LED.
    The issue is not the device. Period. (hate to say that, but given the data we now have, all it can be).
    If the power is present on the leads of the device, and not in the plug, the issue is more likely a poor solder joint where the plug hits the board.
    Dave
     
  9. ScaleCraft

    ScaleCraft TrainBoard Member

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    One other thing...trying to blow up the picture as large as I can....
    Long Shot....if the through hole plating is bad or missing, and the solder is only on the back (solder) side, and the lead of the device is not touching the pad on the component side, all it takes is one side, we'll know if we get zero reading on the scraped pads near the plug.
    I do not see a solder ring on top of the board at the device leads.
    Dave
     
  10. lexon

    lexon TrainBoard Member

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    Remove the device in the center. Four of six holes are part of the circuit for each side of the DCC signal. Look at my photo of the board without the device.
    The two copper traces connect to the LED and resistor go to the two outer circles which are around six closely spaced holes. Four of those holes are used to connect the track connector the the DCC connector from the cab.
    I am using a lighted Optivisor for magnification and I can see all the copper traces just fine.

    Rich
     
    Last edited by a moderator: Jan 21, 2013
  11. Old Reliable

    Old Reliable TrainBoard Member

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    The diode in question is not a unidirectional diode (with a band), but a bidirectional diode. More specifically it is a transient voltage suppressor or TVS. They are used to protect circuits and this particular one can with stand 1500 watts of energy for a very short time. They are generally used for a cushion in the time between a short and a fuse or other circuit breaker activating. At least thats how I am familiar with them. I'm sure there is a lot more to them and I am no expert. TVS diodes are commonly used when running modern o gauge trains with electronics on an old transformer from the 50's. In the very short time between a short circuit and a circuit breaker activating a huge voltage surge can be thrown into delicate electronics. A TVS activates very quickly - a picosecond or so. You should read ac voltage across the tvs- one meter lead on one leg, the other meter lead on the other leg. I just wanted to give a little info about the mystery diode. I realize that we are past that point in the troubleshooting. This was just an fyi for anyone that might not know.
     
  12. maxairedale

    maxairedale TrainBoard Member

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    Hi Jim,

    I use a different brand DCC system but I have been following this thread.

    I really can't give advice on how the system works, but would like to ask if there is power on both sides of the Black thing when following the respective traces. When you said "Power got to the diode not through it.", what do you mean? Was your friend following one trace up to that point and then moved the probe from one side of the black thing to the other or did your friend put the probes on both sides of it at the same time?
    It is mounted in the two holes that Lexon circled in the following

    [​IMG]

    I have marked the same location in your photo where it passed through the PCB.

    Clipboard01.jpg


    Gary
     
  13. ScaleCraft

    ScaleCraft TrainBoard Member

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    That's what I've been asking since page three, I think. No power at the points circled by Lexon, now on page 8 we suddenly have power at those points, but none at the output plug.
    A await the final report.
    Dave
     
  14. lexon

    lexon TrainBoard Member

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    Four of the six small holes between the two large holes with black circles are part of the path on both sides of the PC board.

    Rich
     
  15. ScaleCraft

    ScaleCraft TrainBoard Member

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    Yeah, I know. I had looked up a photo of the component side so I could trace it all out.
     
  16. HOexplorer

    HOexplorer TrainBoard Supporter

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    I'm an electrical dummy. I should have said, he got a reading using the om meter, not 'power.' Jim
     
  17. ScaleCraft

    ScaleCraft TrainBoard Member

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    Okay, ohmmeter. Reading what?
    What did you measure?
    You still have no power on the legs of the device, yet the LED lights?
    Dave
     
  18. HOexplorer

    HOexplorer TrainBoard Supporter

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    Correct no power to the legs of the 'whatever it is diode.' Powe stops at the light. I'm calling NCE tomorrow and giving them this thread address an see what they think. Is there anything I could have done when I initially plugged the whole set up in when I got it back from NCE the second time. Is there some possible short on the layout that could have fried it upon applying power to the power panel and killing the diode? Jim
     
  19. ScaleCraft

    ScaleCraft TrainBoard Member

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    If the device is shorted, it would shut down the system, and NO red LED. If open, it would work just like the one Lexon has with no such device.
    If it's half bad, as in one direction, it would do some odd things, possibly half power, and usually if shorted in one direction get warm....possibly very warm.
    Granted, the LED doesn't take much voltage to light, but it's certainly more than nothing (zero).
    Dave
     
  20. HOexplorer

    HOexplorer TrainBoard Supporter

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    Thanks Dave, Makes sense. NCE will ask me again if my layout is causing the issue. It all runs on DC so I'm not sure any of this is my fault? Jim
     

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