Converting Athearn SD40-2 to DCC HELP!!!

skippygp123

I gave my grandson a new (2002 dated) Athearn SD40-2 engine for Christmas.  I didn't realize it wasn't DCC ready until we opened the box.  Can someone walk me through the necessary steps for conversion to DCC?  I have no idea what is necessary or how to do it but have the parts diagram from the box and am handy with tools. 

If someone can tell me what kind of decoder or other parts are necessary and what I need to do, I am sure I could do the mechanical work.  I just don't know where to start.

Thanks for any help you can give me!

With Athearn there are two basic types of DCC conversions, depending upon the age of the unit.  The older units require a little bit of wiring.  Here's the Digitrax installation manual for a typical Athearn locomotive  http://www.digitrax.com/ftp/dh123at.pdf   .  For the newer models, they have a DCC socket.  For them all that is required is to plug in the decoder.  Here's the Digitrax manual for this type of decoder installation  http://www.digitrax.com/prd_mobdec_dh163d.php   .   For these decoders you just unplug the included harness (they are included for other locomotives that many require hardwiring) from the decoder and plug the decoder into the socket on the locomotive. 

Obviously other manufacturers, including NCE, make decoders for Athearn locomotives. I'd suggest either reviewing the documentation that came with your SD40-2 or pop the shell and see if there is a DCC socket or not.

They are not too bad.  Here is how I did mine.  I have done 3 this way.  Most any decoder with wires should work.  I like to use one with a 9-pin JST plug, for testing and changeouts as needed.  A TCS T1 with Back-EMF runs these Athearn engines pretty good.  I was not pleased with the Digitrax DH123 I started with, so they were changed out.

 http://www.fuzzyworld3.com/3um/viewtopic.php?p=9659#p9659

The newer RTR SD40-2s have the Quick-Plug board, makes life a bit easier.

 Being it's date is in 2002 I'm assuming it's a blue box unit. These are pretty easy to do once you've done a couple. Here's what I do on blue box units.

Remove the shell from the chassis. On the BB SD40-2 the shell is held on by 4 lugs, 2 on each side. Simply spread the sides of the body and these will release.

Remove the contact strip from the top of the motor. This is the metal strip going from the motor to the trucks.

Carefully pull the motor up out of the motor mounts.

Turn the motor over. On the bottom are two metal tabs. These must be removed. I just break them off.

Place a strip of electrical tape in the bottom of the motor well between the motor mounts so the motor cannot make contact with the frame.

Carefully solder a thin wire (18 - 22 gauge) to the strip on the bottom of the motor.

Remember the strip that was on the top of the motor? Put it back on and measure 1 inch from where the clip snaps onto the motor and cut off the rest so that the strip sticks out 1 inch from each end of the top of the motor.

Cut a piece of wire long enough to reach from the contact arm of the front truck to the contact arm on the rear truck and make sure it has at least a couple of inches of slack. Solder one end to the front contact arm and the other end to the rear contact arm.

Put the motor back into the motor mounts and remount it into frame making sure the drive shafts go back together properly. Make sure the wire that was soldered to the bottom of the motor is sticking out a few inches so you can get to it easily.

Solder the red wire of the decoder to the contact arm of the front truck.

Solder the black wire of the decoder to the headlight clip.

Solder the gray wire of the decoder to wire that is soldered to the bottom of the motor.

Solder the  orange wire of the decoder to the contact strip on the top of the motor.

For the lights I use 14 volt 25 mA light bulbs that I getr from Radio Shack. These have 2 wires, red and white. I solder the decoders white wire to the white wire on one light the I solder the yellow wire of the decoder to the white wire on the other light. I cut a piece of wire that's long enough to go from one end of the shell to the other end and solder this to the red wires of both lights. I then solder the blue wire of the decoder to the red wire of the front light.

Position the decoder and wires so the wires are on top of the motor and the decoder is at the back of the motor just above but not touching the rear brass flywheel.

I then position the lights in whatever way will place them in the proper position behind the lenses. Ask 25 people how to do this and you'll get 25 different ways to do it.

Thank you, to everyone who wrote to help me out.  I haven't taken the shell off yet but the parts diagram doesn't show any kind of plug so I'm assuming that it isn't DCC ready.  I'll have to check out the various decoders and find one that I can afford.  Is one brand better than another? 

I noted that someone mentioned they had trouble with Digitrax and Athearn engines.  Is this normal?  I certainly don't want to put in anything that is going to make problems for my grandson.

 Most all decoder makers make wired decoders.  Usually around $20 or so.  I prefer having a plug, to swap out if there is a problem.

I am not fond of Digitrax decoders in Athearn engines.  To me, they run better with TCS decoders, with the Back EMF.   The TCS decoders also handle DC running better as well.  Not sure if that is a consideration. 

WSOR 3801

 Most all decoder makers make wired decoders.  Usually around $20 or so.  I prefer having a plug, to swap out if there is a problem.

I am not fond of Digitrax decoders in Athearn engines.  To me, they run better with TCS decoders, with the Back EMF.   The TCS decoders also handle DC running better as well.  Not sure if that is a consideration. 

The Digitrax DH163AT decoder  http://www.digitrax.com/prd_mobdec_dh163at.php has Back EMF and solderless installation on older Athearn units.  The DH123 decoders do not have Back EMF.