This is the stock model. It has a truck-mounted Rapido coupler on the tender, and a fixed dummy coupler on the front. I decided to leave the front coupler alone.
To remove the rear tender truck, you have to pop out the center wheel. Once done, you can remove the screw that holds the truck in place.
The next step is to remove the old coupler from the truck. I tried popping out the coupler from the coupler body but was not successful. I used a thin razor saw and cut it approximately where the line is drawn in the photo. A little filing is all that is left to do to complete the work on the truck.
The next photo shows the parts for the conversion. The truck was re-installed on the tender so that I could determine if a shim was needed. I used the Micro-Trains 1015 coupler. You can also see the Micro-Trains coupler height checker tool.
Well, as you can see from this photo, there was a substantial height difference between the under side of the tender frame and the ideal vertical location of the body-mounted coupler. The height difference turned out to be 0.050".
Here you can see the coupler being installed. The hardest part was getting the coupler to lie still on the tender body so that I could apply the glue. The white under the coupler is the shim. This will be painted black in the future. I used Testors Plastic Cement to mount the shim to the body. I tried all sorts of ways to hold the coupler still and in position, but nothing worked. Then I thought about balancing something across the coupler. A toothpick turned out to be the perfect weight match. Then I lightly touched each side of the coupler with a small brush wet with the Testors glue and let it get a better grip. After about 20 seconds I came back with the brush and put on more glue. I took this photo while everything was drying, and I don't dare touch it until tomorrow! Update: While I was installing weights in the tender, the coupler fell off. Glue doesn't seem to work too well. I took the time to install the coupler using the Micro-Trains screws by drilling a hole and tapping it. It works great now.
My first objective was to take the locomotive and tender apart to see what we're dealing with. I couldn't find any information in books or on the Internet about how to convert this locomotive to DCC, so this article describes my feeling around in the dark (also known as "gaining experience"). The locomotive and the tender are mechanically connected through a drawbar. Electrically they are connected through a cheap wire and a plug. The plug is next to impossible to connect or disconnect, so that will need to be improved. I am planning on installing the DZ121 decoder (current decoder at the time) in the tender, and so the locomotive and the tender will be permanently wired together.
Here I snapped out the center wheel of the truck so that I could reach the screw that holds the truck to the tender underbody. Once the screws are removed, the various parts that make up the truck can be easily removed.
Thanks to Doug T. from the Yahoo groups n_scale mailing list I was able to take the tender apart. The lines on the next two photos show the "nips" that hold the tender body to the underframe. These need to be pressed in to loosen the two parts, but they don't go willingly!
Here is the one on the other side of the body.
The next picture shows the tender floor. The trucks are screwed to the metal weight on the floor. The weight also doubles as the conduit of the engineer's side track power pickup of the tender wheels. The wire is soldered to the weight.
I had to figure out how to power the decoder from the two rails of the track. Jim Hinds (Richmond Controls) gave me a wonderful, and obvious, solution: reverse the wheels on one of the trucks. That way one truck picks up electricity from one track, and the other truck from the other track. That solved the pickup problem, but both trucks are connected to the wipers, which in turn are both connected to the one weight in the tender frame which has a connector soldered to it. My solution was to cut the weight in half. To be able to take out the weight from the underframe, slightly pull the plastic part away from the lips on the weight.
Here the weight has been removed from the underframe.
The weight cut in half, and the tools that made it possible.
Now that the weight is electrically disconnected, I had to figure out how to connect a wire to those weights. Solder doesn't hold. I don't have machining equipment to drill and tap a screw hole in the weights. Finally I noticed that if I solder a thin wire to the wipers and routed the wire through the underbody, the trucks would still maintain their freedom of movement.
The next photo shows the other truck's wire hooked up as well. In addition, this photo shows the two small strips of 0.040" thick styrene that I glued together and placed in between the two weight halves. That way they are guaranteed not to touch, nor are they going to shift.
I installed the Digitrax DZ121 decoder in the tender using velcro that has tape on the backside of each side of the velcro. One was taped to the weight and the other was taped to the decoder. This way the decoder is removable should that ever be necessary. After installing the decoder I soldered the red and black wires of the decoder to the appropriate wires coming from the tender's trucks. The soldered connections were covered with liquid electrical tape. The last step was to use Walther's Goo to glue the two wires to the weights for a neat appearance.
I decided to install a yellow LED in the tender cab. This adds a little life to this locomotive and it allows me to check whether or not the decoder is getting any signal. I decided to wire both the white and yellow wire of the decoder to the LED. That way the LED stays on whether the locomotive is moving forward or in reverse.
The simple schematic diagram of the hook-up. The resistor's value is 390 ohms.
Let's explore the engine now. The cab and spacer nut had already fallen off the locomotive a few weeks ago, so that was easy. :-)
The next photo shows the boiler shell off of the frame. It comes off easily. Near the rear of the boiler, on the sides there are little holes in the shell that take a pin from the frame. Pull the boiler shell out a little bit and you should be able to lift the shell up. This may require both hands at the same time, so watch out for the frame dropping. The shell comes off by sliding it forward a bit.
To gain access to the gears, remove the screw at the front of the frame. I found very liberal amounts of lubricant everywhere.
It is now time to electrically insulate the motor's brushes from the locomotive's frame. This photo shows how a black wire is soldered to the top motor brush. The wire comes from both the front of the locomotive and from the old tender wire.
And here is the view of the front of the locomotive. We need to remove this entire wire by unsoldering it from these two places.
Next comes the removal of the clip that holds the motor in place. The arch of the clip actually goes over the inside edge of the metal ring.
Before removing the motor, be sure to make a mark on the top of the motor so that when you re-assemble it, you can put the motor in in the right orientation. After you remove the motor and flip it over, you'll notice that the clip that is inserted under the motor brush is in reverse direction. This is what makes the locomotive pick up the electricity from the other rail. We are going to pull it out (it comes out fairly easily), and re-insert it with the hole sticking out just like the clip on the top of the motor.
Like so... Then put the motor back in its place, add a little solder to the connector, and solder the decoder wires to the connectors. I put the gray on the top connector and the orange on the bottom. At first I had them the other way around and caused the motor to not turn over at all.
Here's my temporary test contraption. Using tape and toothpick I was able to run the locomotive without having any wires accidentally touch any other metal parts. The locomotive runs but its gears make a lot of noise. I had it working for the next NTrak club setup at a local show.