DCC decoder stops responding for no apparent reason

[wilwahabri]

I recently fitted a Lenz standard Plus V2 decoder to a Lima Deltic model. All went well until yesterday when it refused to move at all. 

 

I am running a DCC++  system based on an Arduino Mega 2560 clone and motor board, using JMRI as the control interface.

 

I have put an oscilloscope on the track and the signals appear to be present, I have a peak to peak voltage of approximately 14 v square wave  at about 8kHz. pulse modulation can be seen taking place when commands are sent to the track.

 

The carriages I  have with lighting are all illuminated  normally so power seems to be getting to the track.

 

I removed the decoder and bridged the track pickups directly to the motor connections and ran the track on DC and the motor operated as expected in both directions with no problem.

 

With the decoder in place and on the programming track When I try to access the CVs I get the error message "No acknowledge from locomotive (308)" and read data returns "Unknown" 

 

I have change out the Mega 2560 for  a brand new unit, and likewise for the motor board. This has had no effect on the problem.

 

As I am building all this from scratch I have no other loco fitted with a decoder to compare results.

 

It looks to me like the decoder has failed, I have read that it is possible that the decoder can "lock up" and needs to be reset, and I have the data for that reset process, but JMRI will not allow me to access the CV responsible.

 

So the questions are:-

 

How exactly do I send a reset code to the decoder from JMRI?

 

Is it likely that the decoder has failed?

 

Have I missed something obvious?

 

Thanks for your assistance in advance

Edited April 19, 2020 by wilwahabri
response

[johnb]

It's a bit of a long shot, but what current does the Deltic draw when running on straight DC?

Lima motors, at least the ones that I have, don't usually draw too much, but how freely running is the mechanism? Does the motor get hot on prolonged running?

 

Could there have been a short somewhere on the loco? That won't have done the decoder any good.

 

As I indicated at the start, it's a bit of guess.

[wilwahabri]

Cracked it! the NEM socket was faulty! it was preventing the plug from seating fully. Sorted that out and all running well again. Must have been pure luck that it ran for the last couple of weeks only stopped when I unplugged the decoder to tidy the wiring! Always the last thing you touch!

 

Thanks for the assist