Finding Rail Diesel Cars also known as Budd cars in N scale with DCC decoders already installed is difficult at best, particularly with Boston & Maine markings. Fortnately, Kato RDCs that are DC are frequently available on eBay either undecorated or even occasionally with B&M markings. Digitrax makes a drop-in decoder for these cars, the DN143K2. The decoder install is considered by some to be challenging, but I would classify it more as finicky since it is a drop-in install that does not require hard-wiring or any soldering. Some minor modification of a couple parts and care in the install is all that is required. This page provides the step by step process I have gone through with 3 separate RDCs thus far.
Parts, tools, and getting the shell undercarriage off the car
Here is the step by step process I went through to install a DN143K2 decoder into an N scale Kato Budd Railway Diesel Car (RDC). This was my second one, so I have documented in detail the steps and some things to pay attention to as you go. Here are the packaged Digitrax DN143K2 decoder and the Kato Budd RDC car.
The only tools required are a very small flat head screwdriver (mine is from a glasses repair kit), a small hobby knife, a small file (triangular worked well for me), and some Kapton tape. The tape is optional but helps for not having wires left showing in the windows when done as well as for helping secure a couple parts better than without.
The first step is to carefully remove the outer shell. For me, it worked well to use my thumbnail to gently spread the shell on one side at a time of one end to get one end partially lifted off and then repeat at the other end.
The next step is to remove the plastic undercarriage piece. This is necessary because the interior seating panel has clips underneath that can only be released by removing the undercarriage. Removing this section is not as easy as removing the shell. The TMTV video suggests gently squeezing from the sides. That didn’t do much for me by itself. What I found worked was to use my thumbnail and a small screwdriver VERY carefully so as not to damage anything and create a slight separation under one side in a location away from smaller parts.
Remainder of the disassembly
In order to remove the seating section, you need to remove the center white clip. The actual points that clip are in the center. To avoid breaking them off, I found it worked well for each side to first lift that side of the clip and then use the small screwdriver to push towards the center on the clip prong itself to get it to release. I repeated on the other side of the clip. There is a pretty good chance when you get the second one that the clip will spring into the air and going sailing somewhere nearby, so best to not be near any radiator floor vents of other things that the clip will instinctively seek out to fall into and be lost. This clip is important when reassembling to ensure good pressure between the decoder contacts and the contacts of the motor and the strips that feed from the wheels.
Before actually removing the seating panel, you will need to remove the two light clips for the light boards at each end of the car. (left) These are easily popped out with a thumbnail or small screwdriver. Once the two clips with the light boards have been removed, it is time to remove the seating panel. This panel is held in the center by two clips that can be seen under the car by the ball joint of the drive train.
In the photos to the right you can see the two white prongs for each of the two clips just to the right and left of the center weight looking at the underside of the car and that the panel also is held at each end on the sides of the car by small L-shaped clips.
I found it worked best to release the end tabs from one end of the car, creating some upward tension on the center clip, and then using the screwdriver from the underside gently pressing in the center clip prongs for that end. I then repeated for the other end. At that point the seat panel should come right off and you will have something like the photo to the left.
If the brass contacts at both ends did not come off, take them off. They should fall or slide right out easily.
The one remaining piece to remove is a white plug which takes up the space that will be needed by the decoder. This is easily lifted out with the screwdriver.
At this point, all of the disassembly is complete.
Installing the decoder board and reattachment of seating panel
Now it is time to install the decoder. A few things are worth pointing out about the decoder to be aware of during installation and also if troubleshooting is needed later. Here is the decoder consisting of the decoder board, two small light boards for the lights at the front and rear, and a small light board with a tiny LED that is for interior light.
Looking at the decoder board, see in the middle photo above that the two contact surfaces are oriented towards the side edges of the board. That side of the board will end up facing down towards the motor contacts. In the third photo showing the top side of the decoder board, notice the longer contacts running lengthwise on the board. This side will face up and will be against the long contacts on the underside of the seat panel to get current from the wheels. Also notice the underside of one of the light boards. Notice on the light board how the contacts are not the full length of the board. The wires will be closer to the center of the car and the end with the contacts will be closer to the end of the car. This is significant later if you find that the light clips are not firmly seated because if there is rocking or looseness, it is the end of the light board with the contacts (closer to the end of the car) that must make firm contact to get current from the wheels. So when troubleshooting later, keep in mind which end of the light boards the contacts are on (end of the car).
Here is the underside of the seating section. As you can see, the contact strips run the full length of the panel. Where the decoder goes, the contact strips are snug against the underside of the panel. At the ends, notice there is separation between the contact strips and the seat panel. This is to allow for the removed contact strips at the ends of the car to be slid between the seat panel and the long contact strip in order to be squeezed between them to maintain good contact.
Start the installation by threading the small light boards and wires up through the hole in the seat panel from the underside so that the decoder is on the underside of the seat panel. Notice that the decoder is oriented so that the motor contacts are closer to the center of the car so they will line up with the motor. You then can snug up the board to the seat panel. This is a little tricky because of how the wires come off the board at the center end. You need to carefully snug up the end the wires are at and gently push just enough to snug the rest of the board nice and flush to the bottom of the seat panel so it should look like this:
Now you can go ahead and snap the seat panel back onto the chassis of the car with the decoder board between the seat panel and the chassis. Be careful to line up the center tabs and the squeeze together to snap in. At this point do not snap the end tabs at either end of the seat panel into place yet. If the end tabs do happen to snap closed, you can always pop the ends up again for the next step.
Recall I mentioned how the contact strip under the seat panel leaves separation from the seat panel at each end. Now slide the metal contacts in place with the long end between the seat panel and seat panel contact strips. The metal contacts should slide straight in and a small pin should fit into a small hole in the contact.
With the contacts slid back into place, you can squeeze the ends of the seat panel back down into place.
At this point, you are ready to make the modifications to the light board clips and complete reassembly. Those topics will be covered in the fourth and final part of this series of posts.
Modification of the light clips and final reassembly
Before installing the light panels in the two ends, it is necessary to slightly modify the light panel clips. Here they are unmodified. Using the small hobby knife and/or small file, you need to cut and file away a small gap for each of the two wires to go through. If you do not do this, the light board will not seat well and will not maintain contact to get power. Note that these clips are small and the plastic is not very strong. So you want to be careful in creating the gaps. I use the small hobby knife to carve away just a slight amount for each gap and then used a small file to actually create the large enough opening. The only reason I even started in with the hobby knife was so it would be easy to guide the file where I wanted the gaps. Here is a clip with the modification.
Notice that the gap is as far to the right and left as it can go. This is very important because of the way the wires come off of the light boards. See below two photos of it. The wires are soldered to the board pointed off the side of the boards. But they need to thread off the end of the board towards the center of the car. You will need to very carefully bend each wire to point off the near end of the board to then fit through the gaps in the clip you just made. (Digitrax would have made it easier by orienting the wires coming off the board in the necessary direction to start with.)
Oriented properly, the light board should snap into the clip with the wires coming out through the gaps you created. Then you should be able to snap the clip back into the car being careful to route the wires around the plastic obstructions. Repeat the same process for both light boards, again being careful on routing the wires so they are not preventing the clip from fully seating.
The one real shortcoming of the Digitrax design is the clip they provide for the interior light board neither clips the board very snugly nor really snaps into place. It just sort of slides into place loosely. This is one of the places I tried using some Kapton tape to assist as well as for taping down the wires to the seat panel so they will not be right in the windows.
Finally, you can snap the plastic bottom back on the car and carefully slide the shell back on and snap it in place. You need to make sure it snaps snugly in place because downward pressure on the light board clips is important to maintain good contact on the underside of the light boards.
As mentioned in the instructions, one issue you may find is that the light boards may be reversed. Both of mine were. They supplied longer wires to the wrong light board so the direction of travel was reversed from which lights were on. This is easily remedied by setting CV33=2 and CV34=1 to reverse the mapping of the lights.
Have fun with you now DCC-enabled RDC! I hope this was helpful.