Posted by: bgtwindad | March 15, 2011

Decoder Install: Kato NW2

This should be a long post, but not too long.  We’re going to install a TCS K3D3 DCC decoder into a Kato NW2 N-scale locomotive.  The Kato NW2 was designed to be DCC-ready, and the TCS K3D3 is a drop-in design, so that makes this a very easy, 15 minute or less install.  If you have one of these nice little switchers, you should not fear this task at all.

This install procedure should also work for the Digitrax DN123K3, which is also a drop-in replacement for the Kato NW2, though I haven’t tried it myself.

Let’s get started, shall we?

Step 1: Remove the shell

The shell is basically press-fit over the chassis.  To remove, simply pull gently but firmly down on the trucks and it should slide off.  It may help to spread the shell just a bit with a toothpick on either side, but I can generally nurse mine off with some steady pressure.

Once the shell is removed,  you’ll be able to see the light board on top of the chassis, with the two tabs that connect the light board to the motor brushes (round things in the center of the chassis sides)

Step 2: Remove the motor clips

Next up, we need to carefully remove the motor clips.  These are the little metal things that look like frogs hanging from the light board with their legs wrapped around the motor brushes.  Before moving forward, study how the clip is attached to the light board and the motor brush.  Take a photo or two if it helps you.  You will reinstall the clip onto the DCC decoder exactly the way it is here.

To remove them, take a toothpick or a jeweler’s screwdriver (or tweezers) and gently pry the clip from around the brush.  Be careful, and don’t bend the clip out of shape, as you will need to replace it later.  The clip is springy, so it should pop off with some gentle pressure.  Once the “frog’s legs” are free of the motor brush, gently but firmly pry the clip from the light board and set it aside for use later.  Repeat on the other side.  The clips are identical, so don’t worry about getting them mixed up.

Step 3: Remove the light board

The light board is the circuit board on top of the chassis.  It is tightly held down by tabs in the top of the frame.  To remove, you must push it forward until it slides free of the tabs.  Squeezing gently on the bottom of the frame may help a bit.  Mine was very tight (a good thing), but with firm, steady pressure, it will slide forward and come loose.  I used a screwdriver blade as a pushing tool.  Probably not smart, as it may well have slipped and damaged the LED on the end of the board.  Better to use something a bit larger and more blunt, and less likely to slip.

Once you have slid the board free of the tabs, it can be lifted from the chassis and set aside.  I kept mine, but there’s not much reason to.

Step 4: Install the Decoder

To install the decoder, you simply place it on top of the chassis and slide it back under the tabs.  A couple of details, though.  The “body” of the TCS decoder is just slightly longer than the space between the tabs, so it won’t lay flat like the light board did.  To get around this, tip it up slightly and “tuck” it under the rear tabs just a bit, as shown above.  It will then lay flat and you can slide it into position.  It is a very tight fit (like the light board was), so you will have to press firmly to slide it into position.  Again, squeezing the bottom of the frame slightly seemed to help.  Finally, you can push the board in too far.  Try to align the clip contacts directly above the motor brushes so the clips will install easily.

Step 5: Reinstall the motor clips

Next we must reinstall the motor clips.  Press the clips directly onto the clip tabs, just like they were on the light board, and then snap the “frog’s legs” around the motor brushes.  Make sure everything is lined up straight, and you are almost finished.

Step 6: Reinstall the Shell

This actually turned out to be the trickiest part of the install.  For some reason, when removing the shell on my NW2, the cab detail part tends to drop out of position.  When that happens, the chassis won’t go back in exactly right, and it’s not immediately obvious why.  Here’s what the cab detail looks like from underneath when it’s loose…

And here’s what it looks like when it’s been pressed back into its correct location…

Double check this, and then slide the shell over the chassis until it snaps into place.  Congratulations!  You’ve just installed a DCC drop-in decoder in your Kato NW2!  You can now take it over to your programming track and customize it, or drop it on your layout and have fun!

This is a very simple install, about as easy as it gets.  If I weren’t stopping to take pictures and notes, and talking with two very excited kids, I could probably get it done in well under 10 minutes.  As it was, going very slowly with distractions it took 17 minutes total.  With this install, there’s no soldering, no wires, no insulating tape, no tricks at all, and you get a nice, smooth running loco “out of the box.”

If you’ve tried this install and have comments, questions, or ran into problems, feel free to share them here!



  1. […] going to tackle another “easy” DCC decoder install.  Not quite as easy as the Kato NW2, but still very much a beginner project.  Today, we’re going to install a TCS IMF4 decoder […]

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