Installing A Digitrax Sound Decoder In An Older Atlas RS3 Diesel Locomotive

This page is about installing sound in an HO Atlas RS3 diesel. 

If you've landed on this page you're probably comfortable with installing non-sound decoders in locomotives. If not, you might like to have a look at my other page about installing a basic decoder in an HO Athearn switcher.


Decoder installation in an Athearn switcher

Atlas RS3 DCC sound installation
Atlas RS3 Digitrax sound install

I had two older unpainted Atlas RS3 locomotives sitting in boxes. I think one of them must have been bought in the early 80s. The other was more recent. First of all, I got up the courage to paint them in my Utopia Northern paint scheme.

Then I began the Atlas decoder installation.

This was a lot trickier than a simple install because there isn't a lot of room inside the RS3 shell. This often is the most difficult problem to solve, especially for the speaker enclosure. Oh well, fools rush in...

Here are the various stages I struggled with:

  • The weights had to be shortened to provide space for the speaker enclosure and the capacitor.
  • The old decoder board had to be removed and discarded.
  • The decoder had to be hard-wired.
  • New LED lights had to be installed. This was to replace the previous lighting track that carried illumination to the front and rear of the shell.

 If you've visited the other DCC pages on my site, you will be aware that my railroad uses the Lenz system. This was the first time I had installed a Digitrax decoder. Thanks to the NMRA and the DCC Manufacturer's Association there are compatible standards.

Damon, one of my "go-to guys" at Credit Valley Railway hobby shop in Streetsville, Ontario, recommended I use a Digitrax DH165A0 mobile decoder circuit board replacement because it was a "drop-in" to replace the original board. Well, it was, sort of. Unfortunately, my engines were so old that the original boards did not have those little plastic release tabs at the ends. The board fit OK, but I was going to have to hard wire to the pads. Removal of the old board followed the same procedure as outlined in the instruction sheet for an Atlas U33, except for this plastic tab difference.

Tip: The convention is that the power leads from the trucks are always the OUTSIDE pads at each end. Just route the new wires from the side frames to these pads, red on one side, black on the other. The wires from the decoder to the motor are a little harder to wire because of the tight fit. Basically, you have to reconnect the wires to the decoder in the same configuration as the factory board. Take your time and use heat shrink tubing.

  • Test the installation on the programming track before proceeding.

Install the lights

The recommendation was to use Yeloglo White LEDs from Miniatronics (Model 12-310-10). They give a great light that simulates incandescent bulbs.

I used epoxy to glue in the LEDs. I find it is often a good idea to use a tube of styrene or brass to fix the LEDs where you want them. This also works with grain-of-wheat or similar incandescent bulbs. I now try to avoid these because of the heat build up when using 12-16 volt bulbs. Both the bulbs and the resistors can get really hot.  Not good for decoders and definitely not good for plastic shells! 

  • Again, back to the programming track to test.

The other great thing about the DH165A0 decoder is that it is compatible with the Digitrax SFX004 Soundbug decoder. This plugs right into the DH165A0 (at the right end in the above photo).  I think I installed the DH165A0 upside down, not that it matters as long as it physically fits.

Tip: The Soundbug can be installed as a stationary decoder above or below a yard and double-headed with a non-sound equipped engine. 

Tip: This was another tip from my "go-to-guys". I have a Lenz-equipped diesel switcher that works a major yard. It doesn't run on the mainline to other towns. I have it double-headed with a Soundbug so that I can control the sound effects as I run the engine. It's a good compromise, especially when you have an engine that would be really difficult to convert.

I thought there would be more room in the cab area for the speaker and enclosure. Wrong. As you can see, I have the speaker tucked up at one end of the shell with the capacitor at the other end above the drive shaft. I used a 1/2" Soundtraxx speaker baffle kit with a 1/2" speaker. The Soundbug comes with a 28mm speaker and 330uF capacitor. I couldn't figure out how to make room for it so I'll keep it for another installation.  I might try running it in parallel to the stationary one in the yard to spread the sound around.

Even the 1/2" speaker was too big "as is". I had to cut it down a little to get it to fit so it wouldn't rub against the drive shaft or the trucks. I used double-sided carpet tape to hold things in place.

The biggest problem I had was getting the wires to route so they wouldn't bind on the flywheel or the drive shaft.  The headlight wires need some slack so the shell can be removed.

The sound in both engines is a little weaker than I like, but hey, it works.

 It was suggested that I might try removing the radiator grill in the roof and installing the speaker facing up below the grill. I bought a sheet of Apex Slotted pattern .008 Brass screening from Plano Model Products. 

I had to do this carefully and leave a lip around the top so I could attach the speaker underneath. This gave more clearance above the drive shaft where I was still getting some rubbing. I adjusted the sound levels in Decoder Pro. It was time to put the handrails back on and switch some cars in Utopia.

RS3 engines switching Utopia
Atlas RS3 locomotives at Utopia

Go from "Atlas" to Athearn decoder installation.

Go from "Atlas"to Installing a decoder in an old Mantua 0-6-0.

Go from "Atlas"to Isolating a motor in an old brass diesel.

Return to the DCC page from Atlas RS3 installation.

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