Intro
This page shows how I installed the Digitrax DZ121 decoder into the Kato 2-8-2 Mikado. I used the instructions of this site as my go-by. It is an excellent resource. Combined with the photos on my web site, you will be well on your way to successfully upgrading this great little engine.

This is the parts diagram that comes with the locomotive. It doesn't give any information about how to take this delicate locomotive apart. The web site referenced above does a really good job of how to do this. Also see my separate article on how to do some basic disassembly.



Preparation
Using a knife I cut the circuit board paths to the LED.



Next, I soldered the white and blue spare wires to the right and left side, respectively, of the circuit board in front of the cuts I just made. This allows the LED to be controlled by the decoder.



Back to the locomotive. Here I have carefully removed the motor after marking its top with an arrow pointing to the front of the locomotive. This arrow not only indicates the correct direction, but also which side of the motor is up.



I removed the brushes. They have a cap, and under the cap is a trigger-happy spring, so be extremely careful. It will fly away on you. I placed the contents of the brushes in the locomotive's case top so as to protect them from magically disappearing.



Soldered the leads to the brush caps.



Attached the brushes back to the motor.



Motor has been reinserted into the frame. Getting the gears to line up and connect again was a bit of a struggle. Patience is important.



Reinserted the light board.



Installing The Decoder
Removed ¼" of material from the tender floor so that the wires can clear the floor. Compare this photograph with the one above to see how much and where the material was removed.



No, this is not a new species of octopus. It is the decoder attached to the contact strips.



This was one of the most frustrating and time-consuming steps of the installation. The contact strips have to be placed just right, however the wires of the decoder are significantly stronger than the weight of the contact strips, hence the slightest movement of the decoder and one of the contact strips pops out its spot while maneuvering the other. Continuing with deep breaths and not letting frustration get the better of me, I was finally able to get it into place. Carefully positioning the tender floor, which holds the contact strips in place.



The massive spider web.



This photograph shows the left side of the locomotive. It gives you an idea of how to route the wires. This is different from the way the web site, from which I got the textual document, describes how to do it, but I wasn't able to get the locomotive shell back on the frame based on the way they described it. The wires are routed underneath the engineer's seats.



Here's a shot of the left side of the locomotive.



If you have read this page before, you will remember that I wasn't happy with all those wires hanging out of the locomotive. Also the forward light didn't work anymore. Finally, when I placed the tender shell back on, the four wires were so tight that the locomotive actually derailed on anything but a 26" radius curve! This was unsatisfactory. I removed the white and blue wires from the decoder and the light board. This left the dark gray and orange wires that provide the motor contacts. The next photo is a shot of the locomotive put back together. It now performs flawlessly. At some point in the future we will come back and paint the orange wire black.