Major DCC issues.

Discussion in 'Talk' started by Scale7JB, 31 October 2018.

  1. Steph Dale

    Steph Dale Western Thunderer

    Ref your remaining fault: It's not a short. You've described an open circuit, if locos with stay alive are running across, it tests open circuit and locos without keep alive stall then its an open circuit.

    Sorry I can't elaborate more, I'm v. Busy and at work...

  2. Kev T

    Kev T Active Member

    good news about finding the fault.

    The volt reading across the zones has me a bit confused. I'm not being definitive about this because I'm not completely sure of my facts. I suspect that you can't measure across two different circuits that are electrically isolated from each other and get meaningful readings. My guess is that the two zones are electrically isolated from each other because the DCC voltage is not referenced to anything, floats. They will only be connected when there is a connection between the zones, i.e.when a long loco bridges the gap electrically. It would be interesting to get the opinions of an electrical engineer who has more knowledge on this.

    If the above is wrong then the fact that you get no volts across the gap suggests that the tracks are in phase. Did you measure across the gap across the rails and get a voltage?

  3. Scale7JB

    Scale7JB Western Thunderer

    All good news as above.

    We are still getting a difference in speed when a loco passes from one power district to the other (scenic section -> fiddle yard), but I think this is something we will have to live with for the time being.

  4. simond

    simond Western Thunderer

    JB, Robin,

    good news, it appears. I am not familiar with "zoneshare" but had a look - are you wired up like their graphic ?



    The suspicion is that you have a "red to blue" situation at one or other zone boundaries.

    It "should" be simple, and I don't imagine that you can reverse the connections except between the outputs and the track (unless you have another booster that is connected to a section of the track in parallel with, but not through the zoneshare - see below). It would appear that the zoneshare is all PCB based, so it's not going to have a reversed connection internally.

    I presume you have it so that the whole layout does not shut down if one loco on one district has an issue. At least it suggests that all your track supplies radiate from a single point, and that makes a test quite easy. Looks like a useful unit, but not sure if extra boosters would not be a cheaper and more robust option.

    Anyway, I would suggest temporarily connecting all the red track feeds together, ditto the blue feeds, and connect both direct to the main booster, without a zoneshare, or anything else, and see if your boundary problem still exists. If it does, you have a reversed track feed somewhere, but you would be able to find that with a meter, if all the track supplies are connected to the same terminals on the same booster.


    You can then check the polarity across the boundaries using a multimeter set on 20V Ac or similar - you should have zero volts between the adjacent rails (A-B & C-D) and track voltage between opposite rails (A-C, A-D, B-C, B-D), of course.

    If your multimeter is playing the goat, turn off the power but leave it connected as suggested above, and use the multimeter on resistance. Connecting the probes together should show zero, and disconnecting them should show "high" or "1" or infinity or something similar, so you can verify that it's working. You could also use a battery and bulb, and a pair of probes.

    The resistance between A-B and C-D should be very low, and between opposite rails (A-C, A-D, B-C, B-D) an obviously higher value, though I do not know how high - "very" I expect.

    Assuming that works as expected, and you can drive a loco over the boundary with no sparks and no misbehavior, then you can reconnect your zoneshare and see whether the problem recurs. If so, you know where to look.

    You should not get a difference in speed when driving across a boundary where both sections are supplied by the zoneshare, unless it is damaged. You may get a difference when driving onto a zoneshare section from a section supplied by another booster. If this is the case, I suggest that you disconnect the zoneshare (connect all supplied sections together as above, to a single booster) whilst you sort out the boundary issue between boosters. You can then adjust all the boosters to give the same voltage, (and polarity) and the speed change issue should go away. It will return when you reconnect the zoneshare, because there are semiconductors in the track current pathway. You will need to turn the output voltage of the booster supplying the zoneshare up to compensate for this.

    Hope this helps finally sort out the issue
    Last edited: 8 November 2018 at 18:10
  5. Scale7JB

    Scale7JB Western Thunderer

    Robin, I could be wrong, but I have a feeling I saw the 'X1' dipswitch on the lower position on our unit?

    JB B
  6. Tim Watson

    Tim Watson Western Thunderer

    I’m sure Steve will be looking down from his steam cloud with a wry smile.

  7. Boyblunder

    Boyblunder Member

    Tim, You are quite right about Steve's view and I hope he is looking down and laughing because he had decided to do Bath Green differently within a few days of trialling the system that we have been using. CVP in the USA have replied promptly and say: "Nobody has ever asked that question before. But, regardless, the DCC phasing of the outputs relative to the inputs is fixed. If it is backward from what you want, just reverse the two input wires. This doesn't apply to the A ouput since it has autoreverse capability." So I guess this means that our unit is not constructed incorrectly, the reversal is a feature. Simon, we followed the CVP diagram but you can see the input wires are both printed red so it omits to show the polarity of the input. CVP's reply appears to confirm that the polarity or phase is reversed within the unit, so their red is on the right hand side of their input connector whereas its on the left of the output connectors. This wouldn't be noticed by most users but we are feeding the output from the big NCE booster to the Zoneshare and the output from the smaller one to the PSX-1, expecting the phase to come out in the same order from both, but they don't. We are not using the autoreverse feature because we don't have a loop so D4 is set to off, D1 is set to on to enable the short circuit buzzers. D2 and 3 are set to off so we have a 40ms short circuit delay and that seems to be fine. The mystery is solved I think, although I'm not sure why CVP reverse the output compared to the input and I don't fully understand Steph's point about the open circuit but I expect its correct. The system is working at the moment so I think we will just leave it alone and concentrate on improving the reliability of the 320ft of track, 3 crossovers and 17 turnouts to make it absolutely bullet proof in the next 2 weeks. Ho hum.
  8. simond

    simond Western Thunderer

    Good news indeed.

    I think that it makes sense that the zoneshare might reverse the phase, it’s probably intended to be used in place of a few smaller boosters, and therefore the boundaries are expected to be between its subsections, rather between a sub section and another booster. So I guess their designer would have selected the most convenient / cost effective board layout, without considering it as a constraint. And, as they’ve said, simply invert the inputs if it is an issue.

    I think you will see a voltage drop in the zoneshare itself, you might need to adjust the booster to compensate, so you don’t get a change in speed as a loco crosses the boundary.

  9. Boyblunder

    Boyblunder Member

    Yesterday we dismantled the 8 boards that make up the country end curve and I spent most of the day re-making the joints that were showing signs of acid attack. Put it back together and it all worked, after an initial glitch caused by my forgetting to plug in the cab bus power injector etc. The Zoneshare doesn't cause much voltage drop but there is a notable difference between the PB110 & PB5 outputs which is causing the effect that Jonathan mentioned. The PB5 isn't adjustable which is a nuisance so I'll have to reduce the voltage on the PB110, that means taking the lid off the box and sticking a screwdriver into a pot as per NCE instructions. The voltage difference isn't noticeable with most locos. Curiously one or 2 show it up quite clearly, John observed that it seems to be related to the throttle step set-up on the decoder. I'll adjust the PB110 when I'm feeling brave enough to take the lid off it.

    Going back to Kev's point about volt readings across zones, I was referring to some advice given on the NCE support group site about checking phase miss-matched wiring. It was based on boosters using a common return but as we are trying to follow Alan Gartner's Wiring for DCC advice wherever possible we don't use common return. WforDCC includes diagrams that demonstrate a voltage between zones from different boosters on opposite rails should be measurable, but a voltage across the same rail may indicate a missing earth or a voltage difference between boosters. The NCE manual suggests there is only a need to fit an earth if locos stutter when crossing zones when all other wiring is correct, NCE don't provide an earth connection on the booster cases. Having found the main problem I wasn't going to bother with the 58' earth wire between the casing screws, but having re-read Alan Gartner's advice maybe I will next week. Here is the diagram:


    Attached Files:

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