dcc problems

[flyboy10]

another problem this time one of my locomotives is cuasing the system to short out when placed on the track

[simon1966]

So you know where the short is in this case.  Nothing to do but to trouble shoot the loco and fix the short.

[flyboy10]

ya well ive looked at at everything and i dont see anything how ever im not really sure what all to look for i know some things that could be the cuase but obviouslly im missing something

[cacole]

BIG question:  Steam or Diesel?   If it's a steam engine one of the tender trucks may have gotten turned backwards if the tender wheels pick up power.

If it's a diesel, remove the shell and see if the short goes away.  Examine every wire under magnification to see if there are any stray strands touching where they shouldn't be.

It would also help if you tell us what brand and type of locomotive and decoder you have.

 

[Hamltnblue]

The more info you can provide the better advice can be given. As noted earlier remove the shell and start there.  Also post the details about decoder etc.

[flyboy10]

mrc 1812 sound decoder (its a drop in) atlas n dash 8-40b taken off the shell and the problem persists the only wires are those connecting to the speaker iv checked them I dont see a problem there i checked to see if the edges of the decoder were contacting the frame where its not supposed to i see no problem there either

[Hamltnblue]

Look at the motor connections to the decoder.

Also does your loco have the decoder wedged between the frame?  My atlas N's do.

make sure tht the 2 halves aren't touching anywhere and that the insulating washers are in place.

[flyboy10]

frame halves are NOT touching each other and the decoder is wedged between halves also i checked the tabs the look ok but its impossible to tell where they hit when the decoder is installed also the problem does not start until i align the front truck with the track

[jeffrey-wimberly]

 Then check both trucks and see if there's a problem with either of them.

[Bob T]

 Did the engine run before the decoder was installed? If you can't say for certain, then take out the decoder, and convert back to DC. Run around track, thru curves and turnouts, forward and reverse. Now install decoder and see if the problem is there.

Bob T

[flyboy10]

ya it ran before the install

[simon1966]

Take the decoder out and see if the short is still there.  This will narrow the investigation

[Santa Fe all the way!]

Being into HO all my life Im not aware of how decoders fit into N scale locos. Is he saying that the decoder just sits on the tabs for the pickups? You dont solder them? I like to wrap my decoders in black electrical tape to help with the short problem.

[Hamltnblue]

No, with many atlas loco's the decoder sits in the center and the 2 halves of the frame press against it.  The track pickup on the decoder makes contact with each of the 2 halves.

Funny thing.  I just happen to have one next to my desk with the shell off.  I'll take a quick pic and post it shortly

[Hamltnblue]

Here it is. 

Note the spot where the arrow points.  The 2 halves of the frame are insulated with gromets. The track pickup enters the decoder through an edge connector that wedges inside each side of the frame.  The connections to the motor are contact type as well.  There are no wires in this case.  The LED's are soldered directly on the board. 

[jeffrey-wimberly]

 I wonder if the connections for the motor couldn't be crossed up somehow. Back in the 80's I had a N Scale SD45 from Bachmann that had two tabs that came up from the motor and made contact with the board. If those tabs weren't lined up just right it would short out.

[Hamltnblue]

Motor connections wouldn't cause a short unless they came in contact with the frame. Either way I think it would fry the decoder.