The following detailed description covers installation of a Digitrax DN93 decoder in Kato F3/F7 diesels, either A or B units, as actually performed by the author of this publication, and reflects the experiences encountered during those installations. Since multiple units (4) of the same type were converted from analog to digital, the descriptions presented reflect problem resolution and shortcuts developed.

This is one of the easier DCC conversions to carry out, and is recommended for a first or early-on installation.

The Digitrax DN93 decoder was chosen because it was the most advanced decoder available at the time of the installations. Other decoders that could be used are Digitrax DN93FX, DN140, and DZ120 as well as N scale decoders from Lenz, Wangrow, etc.

The most important factor to remember in performing an analog to digital conversion is to ensure both motor brushes and the decoder orange and gray wires are insulated from the frame. Any contact of the brushes and/or these wires with the frame may result in virtually instant destruction of the decoder.

The first step in the description which follows is to test the decoder for proper operation, following the instructions provided by the manufacturer. The purpose of this step is to ensure any non-operational or dead-on-arrival decoder can be repaired by the manufacturer under warranty. While all decoders carry a warranty for some period of time, usually one year, that warranty expires the minute you cut the wires, which, of course, you must do to install the decoder in a locomotive.

As you carry out the detailed instructions below, also refer to the assembly diagram and parts list provided by Kato with the locomotive. It will help with laying out the parts and understanding the terminology used.

In this installation a Digitrax DN93 decoder is installed in both a N Scale of Nevada (NSN) RRR-0307 Receiver-Redi Retroframe (RRR) and a Southern Digital KF37N Digi-Frame. Installation is identical except that no filing or fitting is required with the Southern Digital frame. An Aztec Manufacturing Company TM3008 TrackMaster frame could also be used.

You can also modify the Kato frame yourself. See the section below.

To install the decoder and modify the frame you will need the following tools:

If you do not wish to purchase one of the retroframes you can modify your own existing frame to accept a DCC decoder. If you have the tools, time and inclination, this approach can save the extra cost of purchasing another frame.

The following process applies to the Kato frame. Refer to the detailed installation instructions for the locomotive in the next section, and follow those instructions to the point where you have the frame disassembled. Then proceed as follows:

• Reassemble the frame using the screws and nuts, but not the spacers, being careful to align the two halve exactly.

• Using the decoder as a guide, mark the frame to indicate the metal to be removed to accommodate the decoder.

• Hold the frame in a vise, and use a motor tool to cut out the marked portion. It does not require great accuracy because it will be dressed up with a file. Remove all sharp edges with a file.

• Use a Dremel #106 1/16" diameter rotary engraving cutter or equivalent in a motor tool to grind the necessary channels for the decoder wires (remember to wear eye protection). The channels need only be as deep as the diameter of the wire. Keep grindings away from other parts. Smooth the sharp edges of the channels with fine sandpaper to ensure the insulation on the wires cannot be pierced.

• Use 600 grit wet and dry sandpaper to polish the entire frame, especially in the areas where metal was cut.

• Clean all of the grindings from the frame.

• Disassemble the frame, placing the screws and nuts in a safe place.

You can now proceed to install the decoder per the detailed instructions which follow, just as if you had purchased a new frame.

Set your browser's left and right margins to 0.5" (File Page Setup) and print out this document. As each step in the installation is completed place a "X" or a check-mark through the bullet. All references to the frame are based on the front being at the top or away from you.

In normal analog (DC) operation, the F3/F7 right frame is connected to the right rail pickup and the bottom motor brush, while the left frame is connected to the left rail pickup and the top motor brush.

• Begin by testing the Digitrax DDN93 decoder for proper operation per the instructions provided by Digitrax.

• If installing the decoder in a F3A/F7A unit, cut the green and yellow wires to a length of ½". If installing the decoder in a F3B/F7B unit cut the white, green and yellow wires to a length of ½". Do not cut these off at the decoder in case you need them if the decoder is installed in another locomotive in the future. There is plenty of room to store these wires in the RRR or Digi-Frame.
  
  Note: you can optionally combine both the white and yellow wires to the headlight of an F3A/F7A unit, if you wish the light to be on when the locomotive is moving in either direction. You can turn the headlight off and on using the appropriate function key on the throttle.

• Twist the wires that were cut together, and wrap a small piece of insulating tape over the ends so they cannot short against the metal frame.

• Remove the front coupler from the locomotive. If this is a MicroTrains coupler, the trip pin must be removed first, then the fastening screw, and then work the coupler backwards and up over the front truck.
  
  If the coupler is the original Rapido coupler, use a small screwdriver blade inserted into one slot at the rear of the pilot coupler housing, then wedge up against the power truck to lift one side free. Repeat the process on the opposite side. This will free the coupler, allowing it to be removed through the pilot front.

• Remove the body shell using the following procedure: wedge toothpicks, 2 on each side, between the metal frame and the clear plastic windows until the tabs are released, then slowly work the shell off the frame. Place the shell aside. Remove the fuel tank, coupler housing (Rapido) or coupler adapter (MicroTrains), and the light cover from the frame.

• Prepare the RRR by removing any flash found upon the castings using files and a hobby knife with No. 11 blade. Do this very carefully with reference to the Kato frame, to ensure no mounting tabs or other needed material are removed. This is not required for the Southern Digital frame, except for minor touchup.

• Disassemble the Kato frame, carefully lining up parts on your work surface in the same order as they are removed and noting what each piece is by looking at the diagram Kato provided with the locomotive.

• Before removing the motor, make note of which motor brush contacts the right side of the frame, and place a mark on the motor (piece of tape, dab of paint, etc.) to indicate the top. Note that some Kato motors are already marked with a white stripe, either on top or on one side near the top.
  
  If you are going to modify the Kato frame yourself, do so now by following the instructions in the section above.

• Before installing the decoder, re-assemble the mechanism using the Redi-Retroframe or Digi-Frame in place of the Kato frame. Install the trucks - everything except the body shell parts and front coupler. Put the assembly on a test track and make sure the locomotive runs as it should, checking both directions, etc. When operating correctly, disassemble it again as described above.

• Pry the brush holders up from the motor housing and remove the contact strips. Replace the brush holders.

• Place the motor temporarily in its mount on the left side of the frame. Holding the decoder in the location it will be mounted, determine the length of the orange wire needed to reach the bottom motor brush cap. Cut the orange wire to that length and strip 1/16" insulation from the end. Determine the length of the gray wire needed to reach the top motor brush cap. Cut the gray wire to that length and strip 1/16" insulation from the end.

• Remove the motor from the frame and solder the orange wire to the bottom (positive) motor brush cap, and the gray wire to the top (negative) motor brush cap.
  
  Note: always remove the motor brush caps before soldering to them. Then lightly sand them to get a good clean surface, and apply liquid flux. Finally, solder the wires to the brush cap.
  
  Do not attempt to solder to the motor brush caps while they are still in place in the motor, as too much heat applied to the brush caps during such soldering may melt the plastic brush housing and permanently damage your motor.
  
  After soldering the wires carefully replace the brush, spring and brush cap into the motor.

• The orange wire will route up the left side of the motor when it is mounted in the frame. Very carefully place insulating tape around the motor brushes so they cannot short to the Retroframe when the motor is mounted in the frame, but still permit full seating of the motor in the frame. This is the single most important step in this procedure.

• The decoder and motor are now ready to be installed into the RRR. With the left mainframe laid out in front of you (front of the frame to your right), install the motor and motor mounts with the orange wire on the bottom and gray wire on the top. Route the orange wire up the left side of the motor in the wiring channel provided on the frame.
  
  Note: make sure the motor mounts are aligned properly, with the two little "nubs" vertical against the frame, i.e. top and bottom of the frame, placed in the little channels in the frame. This is very important to smooth mechanical operation of the mechanism.

• Install the front and rear worm assemblies.

• Install the rear insulating bushing in the frame.

• The decoder will obtain its track power from fastening the red and black wires beneath the front insulating bushing on the frame, via the slots provided at that point in each frame half. Holding the decoder in place on the top rear of the frame, measure the length of the red and black wires necessary to reach the front insulating bushing, plus 1/4". Cut the wires to that length and strip 1/8" insulation from the ends.
  
  If using the Southern Digital Digi-Frame the red and black decoder wires can alternatively be soldered in the slots at the rear of the frame provided for that purpose. The red decoder wire is soldered to the right slot, and the black decoder wire to the left slot.

• Place the black decoder wire in the wire channel at the front bushing, aligning the bare wire under the bushing, and just slightly into the hole. Press the front insulating bushing into the frame.

• Place the right half of the mainframe on the left mainframe, being careful that the orange, gray and black wires remain in the wiring channels. As you are placing the front half of the frame down onto the left mainframe, place the red decoder wire in the wiring channel at the front insulating bushing, such that it will be held in place when the frames are screwed together. Install the front and rear nuts, but do not tighten.

• Install the truck assemblies, and tighten the screws.

• Check your work carefully. Use a continuity checker to ensure none of the decoder wires is shorted to the frame, and the red and black wires are not shorted to the wrong halves of the frame, or to each other. Check that the frames are properly insulated from each other.

• Make sure the white decoder wire cannot short against any part of the frame. Take the locomotive to the layout and test both analog and digital operation. Resolve any problems and test again.

• On the headlight assembly board, cut the left-hand lead (headlight pointing forward) right at the circuit board. Cut the white decoder wire to the required length to reach the headlight board, strip 1/16" insulation from the end, and solder to the lamp lead just cut. Place a piece of tape under the lead so the lead and decoder wire cannot touch the board.

• Mount the headlight board to the frame in the normal manner.

• Test the locomotive to ensure proper operations of all functions of the decoder, both analog and digital. resolve any problems.

• Position the decoder in place over the RRR, and using electrical tape, tape in place. Dress all wires over the top of the frame in the channels so they will not interfere with the body as it is placed back on the frame.

• Replace the light cover and the fuel tank on the frame, then clip the coupler mounting plate in place.

• Replace the F3/F7 shell on the frame, and test once again. Resolve any problems.

• Re-install the front coupler. Installation is complete.

• Test the operation of the locomotive on the railroad. It should operate just as if no modifications had been made. Resolve any problems.

• Place the locomotive on the DCC programming track and set the DCC Command Station to the programming mode.

• Program Configuration Variable "CV29" to "06" (for 2-digit addressing or "26" for decoders capable of 4-digit addressing) then program the decoder to the desired address.

• Carry out a final check of the locomotive on the railroad.

• Record the decoder CV's and address, and the reporting marks of the locomotive.

The conversion is complete. Enjoy your DCC-equipped locomotive.