Digitrax dn126M2 install question

[mu26aeh]

I am using dn126m2 for a lifelike sw9/1200.  I have soldered wires direct to brush caps, taped off frame anywhere remotely possible it could touch and all I get is light control.  No movement.  Reading spec sheet, digitrax states if decoder senses motor is not isolated, it will not run.  You can control functions, but motor will not run.  So it is sensing it is not isolated, what am I missing ?  I grabbed my MT1500 and stuck board in there and it runs so I know it's not the board control that is bad.  On programming track, I can change address etc.

[reinhardtjh]

I haven't done a DN126M2 install yet, nor put a decoder in my MTL SW1500's or Walthers/LL SW's so I can't say for sure, but since the chassis for these are nearly identical try a search here for the various threads about problems with the SW1500 install - there have been several - and start checking your problems against those.  I don't remember for sure, but it seems that motor isolation was a problem before so there may be something that could help.

[mu26aeh]

That's part of problem.  I was one of those with issues with SW1500.  It's how I ended up with this extra digitrax board.  I sent original one back after I ended up installing tcs board in its place.  Digitrax will only replace like boards i.e. dn126m2 for same.  Thinking about sending board any engine to them and say here you install the damn thing ! 

[peteski]

Usinng an ohmmeter/continuity-tsester shouldn't it be really easy to check whether either of the motor leads is shorting to either side of the chassis?  Assuming that you own such a device...

IIRC, one of the problems with installing a decoder in SW1500 was that the exposed components on the bottom of the decoder were shorting against the metal chassis.

[mu26aeh]

I will admit im not a good electronics guy.  I own a multimeter but not quite certain what im doing there.  Where do I place the leads to test this ?  Do I place locomotive on tracks, power on ?

I know I will get grief over this,  but thats how I learn things

[reinhardtjh]

Safest is loco off the track, no power.  Remove the decoder if you can.
If your multimeter has a setting for measuring resistance or has a continuity setting, use that.

With the wires disconnected from the decoder, put one probe on the brush cap or connect it to one of the wires and then use the other probe to touch the chassis.  If you get a resistance reading of zero or close to zero or your meter indicates continuity, then you have a non-isolation problem and have to figure out where something is touching the brush cap.

You do this with both caps/wires.  No matter where you touch you should get a non-continuity or high resistance reading.  Anything else is a problem.  If you can, measure while turning the trucks (as they would on a curve) as well as some shorts only happen when things hit as they move.

[mu26aeh]

Ok so checking things out, meter stays at 1 when touching cap and either side of frame.  I checked verses a dc model, it goes to zero when I do same thing.  I have changed motors, and brushes/springs to no avail.  I have also rebuilt back in DC and tested with 9V battery, engine operates.  The only thing touching cap is the wire soldered to it that leads to the decoder.  Bottom cap has tape over it so nothing can touch there.

[peteski]

Is it possible that some component on the installed decoder is touching the metal of the frame?

From the troubleshooting we have done so far we see:

1. The decoder is alive and responds to being addressed (as the headlight can be turned on and off)
2. The motor leads are ot shorting to the chassis
3. The loco works on DC (so the motor is verified good)

So far, this points to the decoder being defective (its motor driving circuit).  Is there any way for you to test the decoder out of the model using another motor.  I would use test-leads with alligator clips to hard-wire the decoder to the track and to one of my spare (known good) motors and see if the decoder would work at that point.

[mu26aeh]

Is it possible that some component on the installed decoder is touching the metal of the frame?

From the troubleshooting we have done so far we see:

1. The decoder is alive and responds to being addressed (as the headlight can be turned on and off)
2. The motor leads are ot shorting to the chassis
3. The loco works on DC (so the motor is verified good)

So far, this points to the decoder being defective (its motor driving circuit).  Is there any way for you to test the decoder out of the model using another motor.  I would use test-leads with alligator clips to hard-wire the decoder to the track and to one of my spare (known good) motors and see if the decoder would work at that point.

I did that already too.  I have a MT SW1500, I took the TCS board out of there and put the Digitrax board it.  Engine took off, so the motor control works (reason why first decoder went back to Digitrax, when I was installing it in the MT SW 1500).  And I have tape under decoder so don't think anything can touch there.

[nickelplate759]

Does the SW9 work with the DCC board in place but running on DC?
If not, you might also check that the wires from between motor and the DCC board are making good contact with both the motor brush caps AND the DCC board.  If there's an open circuit between the board and the brush cap then it won't run (I had this problem...).

George

[mu26aeh]

Here is a picture of taped frame, and frame with motor installed.

20160320_185516 by Adam Henry, on Flickr

20160320_185550 by Adam Henry, on Flickr

[djconway]

Could the tape-decoder be binding the motor?

[mu26aeh]

Consider this case closed !!   

I tore engine apart again tonight, bound and determined to get it running or in a million pieces after hitting the concrete wall.  Someone over on NSN mentioned the possibility of the frame being slightly too narrow for board, and to file away some of the frame where the decoder tabs sit in.  I rewired from the caps to the board, filed away some material, rebuilt locomotive and set on the track.  I didn't realize I had the power on and fired up, so the engine took off like a bat out of hell !  I have the motor wired backwards (headlight comes on in reverse, off going forward) and it sounds like a coffee grinder but it runs !  Guessing the grinding is the plastic worms, have to find some brass ones.  Will need 3 sets since I have two more to decoderize.  Other two will either have TCS M1's or Digitrax DZ126's since that's what I have at my disposal.  And that I found a bit in my Dremel case that I can use to remove frame material.

[peteski]

Interesting development, but what exactly caused the behavior you described (no shorts, decoder taking programming, and then responding to lights on and off commands)?  How exactly did filing the frame take care of the problem of the non-working motor? 

The decoder must have had good contact with the frame to be able to accept programming and then turn the lights on and off.   Only the motor was not working. Sorry, but this makes no sense to me.

[mu26aeh]

I wish I knew.