Unusual Decoder Behaviour

[Jamesn320]

Hi Guys.  I’ve got some strange happenings with a few decoders.  Or it may be something else but I was wondering if anybody had any ideas.

We have a circle of track set up as a test station.  The track is connected, via a rotary switch, both poles, to a Digitrax Zephyr, an MRC Prodigy and a DC controller.

It all works, has done for ages.  Select the right controller, turn it on and test your train, simple.

Hoverer recently we have been having an issue where DCC fitted locos won’t run or respond unless there is something else drawing power.

For example, a Helgen Class 14 (English OO Scale Loco) with and a TCS decoder fitted.  Runs on the main layout (Digitrax DCS100), runs on my programming track (Sprog and PC), put it on our test track (Digitrax Zephyr or MRC prodigy) and it sits there with both front and rear lights on and will not respond.  But if you put another DCC loco and make it do something like move or simply turn on the sound the class 14 works perfectly.  Now if you get it running and remove the other loco it keeps on running.  If the lights are on it can be stopped and started again.  But if turn the lights off and stop the loco it dies again until you pun the other loco back on?

It’s very strange.  I have done continuity checks through all the wires and nothing is wrong.  Plus if it was shorting the Zephyr or Prodigy would pick it up?  What is also odd, if the analogue function is on the loco jerks when put on the track three times but doesn’t if the analogue is off.  I did wonder if DC power was getting to the track but how, I disconnected everything except Zephyr and its still does it?

And I don’t think it is the decoder, not only does this loco run well else ware but it has happened to a few different locos?

Is it connected to current draw?

Any ideas are welcome.

James

[RBrodzinsky]

Definitely sounds like a signal/power problem, and not decoder.   My immediate first thought is the power supply to the Zephyr (or even the internal regulator).  Do you have a RRampmeter with which to accurately measure the voltage on the track?  And, you might actually want to run the output from the command station through the meter, to the track, to also check current: with nothing on track, with just non-responsive loco on track, with >=2 locos on track.

The other thing to check is the rotary switch.  Is there an easy way to bypass it, hooking each of your three inputs directly to the track (singly, of course).

Does the problem only happen with non-sound locos?   If you put a sound unit on the loop, does it respond normally? 

[MK]

Like Rick said, I would do a direct connection to the test track one at a time, bypassing your rotary selection switch.  Just plain straight two wires and see if the condition occurs.

[Greg Elmassian]

noise on the DCC signal does make sense. Adding a load should reduce the main signal, but will normally reduce the noise even more...

this is one possible theory. do things to clean up the signal.

Greg

[peteski]

Can you disconnect the Zephyr from that circle of track (and from the rotary switch) then hook it up directly to a piece of track and then see how it behaves?

If this configurations works correctly then you know the problem is the loop of track, the rotary switch, or the wiring in between them and the Zephyr.

If it is still not working correctly then your problem is the Zephyr unit (which I suspect).

[jdcolombo]

Peteski is right.  Follow his troubleshooting advice. 

I suspect the Zephyr, too.

John C.