Kato/Atlas U25B starts and stops then does not run and CV8 value reads NoPg

[ChessieFan]

  I have a N scale Atlas/Kato U25B-IIb which has idle for 3 months on My large Yard and today I wanted to run the locomotive and was less than successful.   The locomotive would run forward then stall then run forward again and then stall.  This same process happen when I ran the locomotive in the reverse direction.  I could hear the motor buzzing when it sat on the track. The Locomotive has TCS CN-GP hardwired in. I use the digitrax DCC system (5A Super Chief with DCS100 command station with a DT400 throttle).
  So I placed the locomotive on the programming track and the command station beeped 4 times. I then went into programming mode on the the throttle to read the CV values to set what is happening. The First CV value I read was the CV8. The display should have read CV8=153 for TCS decoder, But instead it displayed CV8=NoPG.  So I left the locomotive on the programming track and switched off the programming track and successfully operated other locomotives that have sat on the yards tracks for the same amount of time.  As frustrated as I am I decided to shut down the DCC system and walk away for a few hours.
  I came about 2 hours later powered up the the DCC system . The N scale Atlas/Kato U25B-IIb  locomotive I left on the programming track was moved over to Yard track and the programming track shut down, entered the 4 digit address of the locomotive into the Digitrax DT400 throttle and the locomotive ran in the forward direction and the reverse direction 3 times each then just shut down.  Therefore I moved the Locomotive to the programing track, switched on power to the programming track and immediately the DCS 100 Command station beep four times. I went to programming mode on the throttle to read the CV values.  I tried to read the CV8 value again and received the display answer CV8=NoPg. Therfore I shut the system down and removed the locomotive to My work bench.
  I am frustrated at this point, Therefore I turned to Digitrax  support page to search for an answer, but that was futile! So I am turning to members of The Railwire for Help!!
  I would greatly appreciate any Help.  Thank You.
 
   
 

[nickelplate759]

The fault appears to be in your U25B w/CN-CP, not the Digitrax system, since other engines work just fine.    Looking up beep codes for the DCS100, 4 beeps seems to indicate a short or other fault.  I'm guessing there's an intermittent short in your U25B.   With a CN-GP, decoder it's possible for either board to short out against the frame underneath it - I'd try covering the bottom of both boards with Kapton tape if you haven't already done that.   I'd also look at the the places where the orange and grey wires attach to the motor and make sure that they can't short against the frame - again, Kapton tape can address that.

[ChessieFan]

 First off Thank You for Help

  What I did was to dissemble the locomotive frame, remove the decoder from the mounting tabs, remove all the existing kapton tape from locomotive frame and motor tabs. Then I proceeded to clean up the locomotive frame of oil and grease. Mounted New Kapton tape on the frame in the locations of where the decoder wires came up from the locomotive, placed kapton tape on the top and sides of the frame where the decoder wires ran between the two decoder tabs and finally placed kapton tape on the motor tabs as well along side of the motor to keep the motor wires from moving. Then proceeded to re-assemble the locomotive and re-installed the decoder.

  I placed the locomotive on the programming track was able to reset the decoder to factory settings. The decoder accepted the factory reset, therefore I operated the locomotive with the factory address of 3 on the yard track with no problems. So return the locomotive to programming track and programmed into the locomotive the four digit address (locomotive number). From there the locomotive operates fine on the railroad.

 From now on I will make sure the locomotive frame half are insulated properly with kapton tape.

[nickelplate759]

Happy to help.  the CN-GP is really handy, but something about the two-board configuration makes them a little more finicky than most other decoders.  They are also particular about having both boards have solid electrical connections to the loco frame (what would normally be the red and black wires).  I had an engine take off full-speed in reverse once because the secondary (normally rear) board had a poor connection to the frame.