Decoder question

[PRSL66]

Replaced a decoder in a GP30 which I bought used and only the rear lamp comes on and no other functions, any ideas? I was leaning to possible motor/windings short.

[nickelplate759]

There's not enough information here for someone to help you much with answers, but here are some questions:

1.Can you describe the GP30 mechanism in more detail  - there have been several variations from Atlas, including one with a Kato mechanism and at least one (I think two, but very similar) with a mechanism made in China.  I'm assuming it's not the original Atlas/Roco, Arnold or Lima models as I can't imagine anyone putting DCC in those!       A picture of the frame would be helpful.

2. What model decoder did you install? 

3. Does (or did) it make any odd noises when you first power(ed) it on?  In my experience a loud, sometimes brief, buzzing is a sure sign of a short, and often a fatal (to the decoder) one.

4. Did the engine run on DC before you installed the decoder?

It's unlikely that the motor windings burned out, but since you'll almost certainly have to reinstall the decoder (best case it can be reinstalled, worst case you need a new one) it's always a good idea to test the mechanism on DC first.

5.  The rear light turns on - when it's supposed to (engine in reverse and headlight function on), or all the time?

Since something lights up the board is getting power (red and black connections to the rail).
There could well be a short somewhere - most likely brush tabs on the motor touching the frame, or possibly between a component of the board and the frame.

[PRSL66]

Atlas GP30- China 2007ish, #42907

Came with factory NCE

Change to Digitrax for reliability

Reads address and accepts change in address

Rear light on constant, no control, no noise.

[davefoxx]

Check the motor tabs for good contact with the decoder board.  That will always result in no-go, but lights will work. 

DFF

[nickelplate759]

As @davefoxx said, make sure that the motor brush tabs are contacting the decoder board.  Also, make sure that they are NOT shorting out to the frame.    I'd use a multimeter to check the points circled in orange and gray for shorts to the frame - be sure and check against both sides of the frame.
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Also, make sure that the four contact points (marked with red and black)  make good contact with the frame.  I don't know this particular decoder, but in general all four of them should make good contact.  If any are loose then you need to either build them up with a little solder or a little piece of bronze strip.

[peteski]

How did the model behave when it still had its original NCE decoder installed?

You mention that the rear LED is constantly on and you have no control over it?  Have you tried a decoder reset (write 8 into CV8)?  I believe that it the procedure for Digitrax decoders.

If you tried that and there is no change, then I suspect the decoder is defective.  If the decoder is not being addressed on any throttle then none of the functions should be on.

You mentioned that you can read and write CV values (on programming track)?   If yes, then take the body shell off the loco and watch the motor and headlight behavior as you reading and writing CVs.   The motor armature should twitch as the command station writes or reads the dedecoder, and often the headlights also flash at the same time.  Actually I think that since you are able to read/write  CVs means that the motor is ok and in proper contact with the decoder.  But still verify this using the above procedure.

If you are still worried about the motor (those rarely fails or short out), remove the decoder and see if you can connect some DC power to the motor leads. Use either a DC throttle if you still have one, or just a plain 9V battery.  I doubt the motor is your problem.

[EL3632]

I corresponded with PRSL66 off the wire, it seems that the problem is simply that the decoder did not take the four digit address it was given. The decoder functions fine on 03, but not on the new address. I suggested adding resistance to the programming track (he uses a Digitrax Zephyr, I suggested a track test light or a lighted passenger car).

[nickelplate759]

Glad it's resolved.   Debugging installs can be incredibly frustrating.

[peteski]

Glad it's resolved.   Debugging installs can be incredibly frustrating.

I'm still not sure why the rear headlight would be constantly illuminated as soon as the loco was on the track (at least that was how I understood the problem description).  Red herring?  While not always feasible. I like to understand causes of the problems I am solving.

And I don't see where EL3632 stated that the problem was actually solved. He just provided possible workarounds, but was the loco successfully programmed with the 4-digit address yet?

[PRSL66]

Thanks everyone for the help and support, problem resolved, glad I joined this site.

[EL3632]

I'm still not sure why the rear headlight would be constantly illuminated as soon as the loco was on the track (at least that was how I understood the problem description).  Red herring?  While not always feasible. I like to understand causes of the problems I am solving.

And I don't see where EL3632 stated that the problem was actually solved. He just provided possible workarounds, but was the loco successfully programmed with the 4-digit address yet?

Yes, that is a red herring. Sometimes Digitrax (and others) decoders turn a headlight on when track power is applied and they are not selected. Not sure why exactly, but it happens. The problem was that the loco did not take it's four digit address, which was stated better in the personal communication I had outside the wire:

…will not answer to 3601 addressing, rear light stays on, but address 03 normal functions motor and light...

This usually means it just did not take the address. It works now, as stated by PRSL66.

I did not say the problem was resolved, but once we got the red herring out of the way, it was pretty easy to figure out what to do. Going to library school, recontextualizing information based on what the system can do is one of the fundamentals, glad everything worked out in the end!

[peteski]

Thanks for the explanation EL3632.

People trying to assist in troubleshooting the problem did not have the advantage of knowing that the loco worked fine on address 03.  That would have totally changed diagnostic process. I suppose that you found this fact out while communicating over PMs.

Just to satisfy my curiosity, were your recommendations about the programming track implemented (and address reprogrammed), or is the loco still running on address 03?

[EL3632]

Thanks for the explanation EL3632.

People trying to assist in troubleshooting the problem did not have the advantage of knowing that the loco worked fine on address 03.  That would have totally changed diagnostic process. I suppose that you found this fact out while communicating over PMs.

Just to satisfy my curiosity, were your recommendations about the programming track implemented (and address reprogrammed), or is the loco still running on address 03?

Correct, this fact was not mentioned in the thread prior to my quotation of the private messages. I agree that it is essential information in this specific context, and the diagnostic process was impacted as a result. Getting to the bottom of things and/or finding the root of the problem is something I am, somehow, good at. Not sure why or how. 

The loco is no longer on 3; PRSL66 factory reset the decoder and then reprogrammed to the 4 digit 3601 address, it now responds to 3601. The resistance was provided in the form of an LED, and it did help.

[peteski]

Correct, this fact was not mentioned in the thread prior to my quotation of the private messages. I agree that it is essential information in this specific context, and the diagnostic process was impacted as a result. Getting to the bottom of things and/or finding the root of the problem is something I am, somehow, good at. Not sure why or how. 

The loco is no longer on 3; PRSL66 factory reset the decoder and then reprogrammed to the 4 digit 3601 address, it now responds to 3601. The resistance was provided in the form of an LED, and it did help.

Thanks!

I also usually do ok in torubleshooting things, but I have been doing that as a profession for about 40 years.  The better the problem description we have, the quicker and easier we can arrive at a solution.