Recently I fitted an Athearn BB F7 A-B set with Digitrax decoders (DZ125’s). They work fine most of the time but sometimes the lead unit won’t start up on DCC. If I switch the block to DC and give the loco a little power then shut down and switch the block back to DCC it then will start up and run just fine. Am I correct in assuming that this is because the decoder is having trouble determining whether or not the current it’s getting is DC or DCC? I’m using a Bachmann DCC system so changing CV’s is out at this time. Is there another way I can correct this or do I continue with the method I’ve been using? Starting the units separately isn’t possible as the two units are hardwired together so they pick up power like a single sixteen wheel unit.
I would assume so. CV29 issue. You may have to set CV29 to a value that turns off DC conversion. If you have access to other make controler at a friends house, here is a link to a table that assists in determining the value to apply.
http://www.cmlelectronics.co.uk/support/digitraxmobilecv.htm
Thank you for the link. That looks like the info I need.
If it’s a “sometimes” thing, then it’s not a CV issue, because that would be more consistent.
I’m going with a loose wire or cold solder joint as my first guess, and a sticky motor / gear train as my second, particularly if this is an older, 3-pole motor. It may have a dead spot.
When the engine doesn’t start, what happens if you keep cranking up the power? Will it eventually take off? Or, if it doesn’t start, what happens if you reverse direction and try it?
It does it’s little trick any time the system is started up cold, ie: that the system has been without power. Sometimes it’s the B unit that does it but mostly the A unit. The motors are 5 pole skew wound type. Cranking up the power does nothing except make the unit that did respond go faster. Reversing direction also does nothing. Only by cutting power, switching to DC and giving them just enough power to move, shutting down and switching back to DCC will both units then respond to DCC. I’m pretty sure it’s a CV problem.
Someone mentioned a few weeks back that he was having problems with MU’d engines. His solution was to briefly lift the one that wasn’t responding off the tracks and then put it back down. This power-cycled the engine and it began to respond correctly. I’m not sure what the problem was, though, or who made the decoders he was having trouble with.
How do you have these two engines set up as a consist if the Bachmann won’t support Advanced Consisting like the better systems? If you have tried setting both decoders to the same address, and if you have CV29 set correctly in both, they should run together okay. It sounds to me like the Start Voltage or Momentum settings are different between the two decoders, and you can’t correct this if you can’t change CVs 2 through 4, or if CV29 is not set exactly the same in both units. DC Conversion should either be on or off in both units.
Reread the original post. Both units are equipped with identical decoders. The locos are hard-wired together so they both can pick up power as a single sixteen wheel unit, so picking one up and setting it back down won’t work because it will still be getting power from the other loco. Except for a change of address (originally 03 reset to 02) the decoders are set as they were when they came from Digitrax. When I turn the system on either the lead loco (most of the time) or the booster loco (sometimes) won’t react to the DCC signal. At this point I turn the throttle back to zero and switch the block from DCC to DC and give the locos just enough DC power to make them move then cut the DC power and switch the block back to DCC. After that they work fine. Their speed is near identical.
I assume you’re using DPDT center-off switches for the transition from DCC to DC. Have you tried just turning off the block completely (leaving everything else on) and then just going back to DCC? That should have the same effect as lifting the engines.
Yes, I am using DPDT center off switches for the blocks. I tried just turning the block off but that didn’t do anything. The more I look at this, the more it looks like a CV29 issue. CV13 controls DC on/off on many Digitrax decoders but not on the FX3 decoders. The DZ125 is an FX3 type.
JW,
Your posts are contradictory. You state that the two decoders are wired together for pick-up. If that is the case, each decoder is receiving exactly the same quality of signal. If they are programmed exactly the same, programmed to the same address, and the signal is the same, then is serves to reason that they should respond the same. Yet, they don’t respond the same or consistently. You state that sometimes its the A unit and sometimes its the B unit.
A few possibilities to explore.
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Like others have suggested, there is some difference in the CV settings between the two decoders. The best way to investigate this is to have DecoderPro read the complete set of CVs for each decoder and compare the two to find the difference.
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The DC option should be turned off.
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Separate each loco sop they are standalone units.
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It is possibile that they switching back and forth from DC to DCC has scrambled the decoder and caused one of the CVs to change. This can happen when a short occurs. Since you are running two units wired together as one it is possible to have one unit short and shut down but the decoder still receive power, and signal, from the second unit.
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Lastly, the problem may lie with the Bachmann E-Z Command system. The E-Z system is also capable of running a non-decoder equipped loco. Since the problem only occurs at start up, it maybe that the DCC signal generated from the E-Z is not a “clean” DCC signal. The decoder gets confused with the dirty signal and goes to DC mode. The flipping from DCC to DC and back clears the signal and the decoder. There type of “confused” decoder response has also been reported by Digitrax users, another system with non-decoder loco running capabilities.
The short of it is that without a better DCC system analyzing and solving such an issue will be next to impossible because you can not read or write CVs to try and
I never said that the decoders are wired together. I said that the locos are hard-wired together. There are two jumper wires between the locos, one connects the frames (left side pick-ups), the other connects the right-side pick-ups. The decoders were installed in each loco as if they were stand-alone units.
As far as I know, the decoders CV settings are as they were from the factory with the exception of CV01 (address) which has been changed from the default address of 03 to 02. I’ll know more when I get the set to a modeler who has a system that will read back CV’s. What I’ve seen so far seems to confirm that it’s a CV problem. It’s not a big problem, just a minor nuisance, but I would like both units to start together as I had intended.
On this point we’re in complete agreement and it WILL be done at the earliest opportunity. I had wanted to keep them DC/DCC capable in case I would be running them on an analog layout at some point, but not if it’s going to make the set act like a bride w
Whether you said it directly in those words or not, what you described is exactly that.
Just for grins why did you choose a DZ decoder when there is so much space inside a BB F unit?
Reading the specs for that decoder it says, “Switching Speed feature for easier and faster access to yard speeds.” Could this feature be causing the issue and can it be turned off?
What do you mean you never said the decoders were wired together!
JW - Let’s go back and look at the prior post.
For it to work as a single 16 wheeled unit, power is feed from all wheels to each decoder. Therefore, the input side of the decoders are wired together
Yes, but even when I broke them up as single units and proghrammed them individually, they did the same thing. Besides which, there’s no difference between the decoders getting their power from the track through a shared pick-up than through separated pick-ups.
Are these relatively new engines, or older BB’s? I’m wondering if they have a high initial startup current requirement. If so, the DCC system may not be able to supply it for both at the same time. How do they respond individually? If they both work fine when on the track by themselves, but they don’t when they share the track, this would be a likely explanation.
Does the Bachmann have its own built-in power supply, or do you drive it with something else? When I started in DCC, I drove my Lenz, which has a 5-amp capacity, with an old train tranformer that probably could only put out an amp. Eventually, I had enough load on the system that I ran out, even though I was far less than the 5 amps of the Lenz. Of course, the Lenz couldn’t put out more than I put in, so I ended up replacing the power supply and getting the full value out of my DCC system.
These locos are completely rebuilt. They have the newest 5-pole skew wound motors and the gears have had any and all flash removed. The gear teeth have been smoothed with the ‘Pearl drops’ treatment. The two locos together pull .75 amps at full stall load, way less than the peak the decoders are rated for. Track voltage drops less than one volt on startup. I thought something must be wrong with my meter so I checked it on my old Athearn PA2. It read .80 amps just like it should for that old dinosaur. It uses a Bachmann decoder. Separating the locos has no effect on the problem. The A unit needs to be DC jumped 3 times out 4 on the systems initial startup. The B unit needs to be DC jumped 1 time out of 4. Never have they needed to both be jumped at once, it’s one or the other. I tried running them separately, same thing. Yesterday it was the B unit doing it most of the time. I swapped the decoders around and now it’s the A unit doing it most of the time. When Charlie gets back from his trip I’ll take them to him and have him set CV29 for no DC operation. That’ll settle their hash. As far as power goes, the Bachmann controller is powered by it’s wall wart. The controller pushes it’s power through a 5 amp booster. I’ve tried starting the locos on initial startup with and without the booster. No difference. Once they start up for the first time of the operation session they run fine. They’ll run all day long, start, stop, forward, reverse, no problem at all.
Don’t you just love DCC … When these type of things happen.
Makes you want to go back to DC and cab control sometimes.
Doesn’t it though! But if I did that, I wouldn’t have little things like this to make my life more interesting.[(-D]
IMO, I think the problem will be related to the E-Z Command generating a dirty DCC signal on startup. Because of the dirty signal the decoder can’t tell whether its receiving DCC or DC power. It goes into “protect mode” and goes into DC compatible mode. Cycling through DCC to DC and back by simply flipping the toggle switch, without shutting down the E-Z, cycles the decoder from DC to DCC mode. Because you’ve tried to run the unit in DCC, the E-Z signal is now cleaned and when you cycle it back it can now read the clean DCC signal.
The other question that will need to be considered and answered is “If you find out that there is a difference in the CVs between the 2 decoders, How did that happen?” The E-Z system is incapable of changing CVs, other than address. If the there is difference, how did it occur? - Factory screwed up with initial programming? Phantom reprogramming? Short circuit scrambling becuase the decoders are picking up power over 16 wheels?