TCS M1 in a Kato SD40

This is another one of those installations where I am using a standard wired decoder on a model that was designed to take a specific board type decoder.  In this case the model is the Kato SD40 built on a mechanism that can use either the Digitrax DN163K1B or the Train Control Systems K1D4 board type decoders.  Releases of the SD40 and SD45 after 2002 use this mechanism.  It can be impossible to know what you have until the body is removed exposing the mechanism.

Here is a comparison of the two mechanisms.

The upper photo is the older version and requires the frame to be modified to get any decoder into to it.

The mechanism in the lower photo is the later version which accepts a board type decoder.


Sometimes it happens that someone gets the wrong decoder because they are mistaken about which version they have.  While the board decoder can't be used on the older version there is no reason a wired decoder can't be installed in the newer version.

Looking again at the newer version of the mechanism and comparing a TCS M1 wired decoder along side it can be seen that there is space for this or other similar small decoder under the LED on the long hood end.

As with my other installations where wired decoders are connected to existing boards, the board receives some modifications.  The first step is shown in this photo.

A small section of the circuit traces are removed in the seven locations shown in red in this photo to isolate the various functions.

Then the capacitor that is installed across the short hood end is removed.  This was added by Kato after it was realized that when running at high speed on DC the trailing end bright white LEDs would flicker.  Since this is not going to be an issue using the decoder it can be eliminated.

Next an additional resistor needs to be added at the location shown in this photo.  The value on the resistor should be the same as the existing one.  They will have either a number 271 (270 ohms) or 561 (560 ohms) on them.  I got mine from other stock Kato boards I had but this type of surface mount resistor can be purchased from Electronics supply sources.

All of the decoder wire connection locations are also shown in this photo.

Just as with the board decoder installation, Kapton tape is placed across the top of the frame and over the sides to insulate the frame from the contact wings that extend down from the board.

I found it works best to install the board on the chassis first then put the decoder in it's place and cut the wires to length starting with the ones closest to the decoder.

This photo shows how I placed the decoder with the wires facing backward but it could go either way.  The wires can either go between the leads of the LED or around to one side.

This photo shows all the wires connected

When re-installing the shell, it should rest upon the tabs that stick out from the frame as pointed out by the green arrow in this photo.