Something I'm not understanding!

[froggy]

There are two tabs on the loco and one of them is having a hard time laying flat.I was happy just to see the lights flicker.But I'm still stumped as to what's wrong and why it won't move.I programed it and set it on the main track and the lights just flicker.

[KingConrail76]

Ok, I have 2 of these Atlas SD-35's myself, both Gold series with decoders preinstalled, So I am going off the diagram paper that came with mine. I am not seeing where there would be a "tab" on the loco other than the black plastic "wire retainers" (#850125).

The tabs you speak of, are they metal and secondly are they supposed to contact the decoder board for electrical continuity? or are they NOT supposed to contact, and are shorting out because they are making contact?

[UpNorth]

The Digitrax link I supplied  shows the two tabs to be the motor contact point and each frame side provides the power.  did you try and put the original board back in and run it as address 0 ?   

[Texas Zepher]

I am looking at the package for the decoder.It is a Digitrax and it's DN163A0.

Oh, wow, another bad assumption.  Are these locomotives HO or N.  This decoder is for N-scale.   If N-scale ignore my prior post.

 noticed one of the metal tabs is sticking up and doesn't hardly want to stay down.I put the decoder back on and made sure it is over the metal tabs.

I hope this isn't one of the metal tabs coming up from the motor.  In that case that would be power going to the motor brushes.   A very important "tab".

[Vail and Southwestern RR]

Now we are getting somewhere!

Those little ears need to be contacting the corresponding pads on the decoder.  Make sure they are.  You can bend them a bit, to take advantage of their springiness, or shim things a bit with some styrene.  Also, make sure the pads on the decoder that are wedged in to the frame are amking good contact.  The fact that the light flickered when you programmed is a good sign, that also indicates that those connections are there.

[froggy]

As I was tinkering with it some more, I got the motor to spin even on the main track. I reprogrammed it to 03.Now it won't spin, does the metal tabs on the motor have to be up or down when the decoder is on? I also see the decoder does not have a square CPU like the pictures show. Without a CPU, would this be a faulty decoder?

[KingConrail76]

I am looking at the package for the decoder.It is a Digitrax and it's DN163A0.

Oh, wow, another bad assumption.  Are these locomotives HO or N.  This decoder is for N-scale.   If N-scale ignore my prior post.

 noticed one of the metal tabs is sticking up and doesn't hardly want to stay down.I put the decoder back on and made sure it is over the metal tabs.

I hope this isn't one of the metal tabs coming up from the motor.  In that case that would be power going to the motor brushes.   A very important "tab".

Guilty as charged, I too assumed HO scale, and COMPLETELY missed the DN designation of the Digitrax P'n'P decoder. (I do use some N decoders in my HO stuff..but not p'n'p style.)

[UpNorth]

The 2 tabs from the motor should contact pads on the underside of the decoder.

the frame halves contact the decoder via the frame clips  and pass power to it.

The CPU is present if the decoder spun the wheels, even once, and the lights flicker.

The CPU may be of a different form factor or redesigned by Digitrax and not show it in the manual. 

Again have you tried to re-install the original light board and test the loco as is.

[froggy]

I found a site with really clear instructions on installing the plug and play decoder for the Atlas SD-35 that I have.It involves soldering wires to the decoder tabs that come into contact with the metal tabs to the motor.I will do that and let ya know what I come up with.It says for this certain application for the SD-35 it almost always has to be done.

[Vail and Southwestern RR]

What you can try first, that is easier, is to just tin the pads the the tabs contact, to make them a bit thicker.

[froggy]

Could you explain, tin the pads???? Also you know I have a MRC Prodigy Express and I was wondering how to and which buttons to use for a sound decoder.

[Vail and Southwestern RR]

To tin the pads, just hold the soldering iron on them for a couple seconds to get them hot, and them touch the end of the solder to the pad, to get a thin yer to run onto the pad.  Remove the iron, and you are done.