Tap Creek

The Chicago & North Western Tap Creek Branch


Step 5 - Motor and pickup wiring

Cut the red, black, gray and orange decoder wires to length, and strip off the isolation at the ends. Solder the wires to the contact strips and to the motor contacts respectively. Here is where each wire go:

· Red – to right-hand side contact strip

· Black – to left-hand side contact strip

· Gray – to the right-hand side motor contact

· Orange – to the left-hand side motor contact.

Note that the decoder is inserted into the pit with the wires going out towards the front, so the red, black, gray and orange wires need to turn backward, go under the decoder and then come up again at each side of the decoder. The picture below shows the installed decoder and the first four wires soldered in place.

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Step 6 - Function output wiring

The function outputs will be wired as follows:

· White wire (F0): front head light and the red rear light

· Yellow wire (F1): rear head light and the red front light

· Green wire (F2): interior lighting

· Blue wire: common return for all three functions.

This means that all wires (except the green) have to be going to both the front and the rear ends of the car. Each wire is cut, and front and rear connection wires are soldered to it. You will need extra wires for this (possibly leftovers from some other installation). Heat shrink tubing is used to isolate each joint. The joints fit at the front of the frame, as shown in the picture below. The blue wire joint is just to the rear of the truck king-pin hole.

Now it is a good idea to test your installation so far. But before doing that, cut a piece of .010” (0.3 mm) styrene into a strip-like shape. Bend each end and mount the strip above the motor contacts, with the bent ends going between the motor and the frame. This is essential! If you do not do this, the contact strips on the underside of the interior detail piece will short-cut the motor! The picture below shows this insulating piece of styrene in place.

Temporarily re-install the interior detail piece. This can be a little tricky, with all the loose wires at the front. But it is doable. Once the piece is in place, use an Ohm-meter to check that there is contact between the contact strips in your home-made holders and the contact strips on the interior detail piece. If not, remove the interior detail piece and reshape your contact strips until you have a good connection. Do also check for any shorts and correct them before you proceed.

Once you are sure everything is in order, reinstall the trucks and put your RDC on a test run. If you experience any electrical pickup problems, please refer to the notes at the end.

Note how the blue, white and yellow wires fork off and runs both towards the front and the rear. The rear wires first go down under the decoder and then emerge again on the sides of the decoder (under the bend in the contact strips). They also go under the styrene piece that isolates the motor contacts.

One of my mistakes shows in the picture. Do not thread the rear white and yellow wires as I did. You should thread the white wire together with the blue wire, and let the yellow wire run on its own on the right side. If you do, you do not have the cross them, as I later had to do, in order to reach the correct locations on the rear LED circuit board.

At this stage I also removed some plastic to make room for the wires when they are eventually soldered to the under-side of the LED circuit boards. I did this in both ends (front and rear). The blow-up below shows the areas I shaved off.

Step 7 - LED circuit board installation

The LED circuit boards are originally designed for ordinary DC, but Kato has made provisions for an easy conversion to DCC. The following picture shows the bottom of an “as delivered” LED circuit board to the left, and one converted for DCC to the right.

What you do to convert from DC to DCC is to remove one of the tiny screws and moving the other one. The next picture shows the same boards but with the original screw locations encircled in blue, and the position of the only remaining screw encircled in green.

Kato has also provided holes where to solder the blue, yellow and white (black in the picture) wires. This is OK for the front LED, but with the function allocation I had chosen the locations of the yellow and white wires must be swapped when soldering to the rear LED board.

Cut the wires to length and solder them to the LED circuit boards. When soldering the blue wire to the front board I also attached yet another strand of blue wire. This wire will be used as common return for the interior light.

Turn the boards over and snap them in place as shown below.

Note that the wires first run in the middle of the frame, on top of the truck king pin. In the picture I have reinstalled the trucks to be able to make sure that the wires do not interfere with the movement of the trucks. Once the wires have cleared the trucks they diverge and go in under the LED board, at the place where I earlier shaved off some plastic.

Note how I had to cross the white and yellow wires at the rear end. To avoid that, thread the wires correctly in step 6, taking into account that they go in opposite places on the LED board, as compared to the front LED.

Step 8 - Final assembly

Cut a rectangular piece of .010” (0.3 mm) styrene, slightly larger than the hole in the interior detail piece above the decoder. Slip it in above the contact strips on the underside of the interior detail piece so that it covers the hole. Reinstall the interior detail piece.

Now, everything that remains is to reassemble the rest – the shell and the underside details. In my case I also installed interior lighting, which I wired using the green and blue wires seen in the picture above. But that is another story...


Electrical pickup

If you experience electrical pick up problems try the following:

· Make sure no wires interfere with the pickup strips (the long bronze strips at the underside of the interior detail piece). They do have a tendency to do that were the wires “dive” in under the LED circuit board.

· Make sure the strips really make contact with the trucks. The strips have a “kink” a little less than an inch from each end. Increase that kink.


Track voltage

Both red LED:s in one of my RDC:s burned!!! I do not understand why, since they were properly wired. My only guess is that they overheated due to me using a too high track voltage (14 V). I have now lowered the track voltage to the proper value for N scale (12 V). I recommend that you do the same. Kato warns against using a too high DCC track voltage together with their interior lighting kit, but apparently the same applies to the front and tail light LED:s.

DZ143 Decoder in RDC