TCS CN-GP Equipped Loco running off program track

[Tom4884]

I just installed a  TCS CN-GP decoder in a Life-Like GP20, put it on the programming track and it takes off at full throttle.   I am presuming some wire is touching something it shouldn't,  but I am at a loss.  The orange and grey motor wires are completely wrapped with kapton tape,  there doesn't appear to be any issues with the yellow,  blue or black wires soldered to the rear pads.  The programming track is stand alone and works fine with other locomotives.   I have done dozens of these installs in older Atlas and Kato locomotives and just finished another LL GP20 earlier today and have not come across this behavior before.   Any help greatly appreciated!

Thanks as always,  Tom

[nickelplate759]

Ah, that sounds familiar.

The CN-GP and it sibling, the CN, are finicky this way.  I had this happen once (and I've installed about a half dozen of them). 

There are two boards, with wires between them.  Each board has two contact points.  All four contact points must make good contact with the chassis.  If not, the behavior you see is one of the failure modes.    I resorted to adding a little solder on top of the contact pads where they go into the chassis slot.

[MK]

I *just* installed a CN in a RS-1.  Like George said, I had to add a little solder to two of the four top pads as they were a little on the loose side.  Since solder is relatively soft, the frame can dig into it and form a good contact.

I didn't have any issues with the decoder.  This is the second time I've done one of these.  I'm assuming that the yellow, black and blue wires are in their right spot (not saying if not, it is the cause your symptoms)?

[Tom4884]

Thanks,  I  use copper foil tape when I need to shim them, conductive on both sides and usually works perfectly.   If you mix up the yellow and blue wires, the lights come on but nothing else works (don't ask me how I know! ).

Tom

[peteski]

Yes, those decoders can be finicky. Both PC boards have to  have a solid connection to the chassis tabs.  I'm curious what DCC system you are using?

[Tom4884]

I have a Digitrax DCS240 system.  I have a separate track connected to the program output, and the system is connected to the computer running JMRI.

[peteski]

If you have a multimeter, have you tried to verify that neither motor lead contacts the chassis halves?
If you are absolutely certain that the motor wires are completely isolated from the chassis then maybe the decoder is just defective?

[Tom4884]

Just to follow-up,  I ended up adding a little solder to the 4 pads on the decoder and that did the trick.  Seems the slot on the Life Like engine is a little wider than Atlas or Kato locomotives and the copper foil tape just was not enough.   Thanks again for all the help!

Tom