This article describes the conversion of a DC controlled N scale Bachmann locomotive to DCC. This was my first attempt at doing a DC to DCC conversion and am happy with the result. The decoder I selected was a Digitrax DN136D. This is an inexpensive decoder and I figured if I did something wrong, I wouldn’t be out too much.
This particular locomotive is a Bachmann Spectrum model. It is a split frame which directly sends the power from the left and right rails to the motor. This meant I had to do a small amount of milling to isolate the motor from the frame. Nothing a Dremel couldn’t handle, though!
First, I had to remove the shell from the frame by removing the screws at the bottom of the locomotive. I was then able to lift the shell off of the frame. Inside the shell is the circuit board that holds the front and rear LEDs. This was attached with a single screw.
Next, I had to figure out a spot to put the decoder. Fortunately there was quite a bit of space at the rear top of the frame. There was enough space to fit the decoder and LED without having to mill down that part of the frame.
Next, the screws that hold the frame were removed and the frame was pulled apart.
In the photo below, you can see the tabs on the right side of the motor. These contact the frame and send power to the brushes in the motor. These tabs are what will need to be isolated from the frame. We will then solder the decoder motor wires to these tabs.
A closer view of the motor removed from the frame.
I milled out around the motor tabs on the left and right frame members. I would mill a little bit, then check with a continuity meter, then repeat as necessary. After I finished milling with the Dremel tool, I used a small file to clean up the edges. It turned out that very little metal had to be removed to isolate the motor.
I then had to figure out how to get the power from the frame to the decoder. I decided to remain with the same pickup mechanism that gets the power from the wheels to the frame. So this meant I just had to get the power from the frame to the decoder. Since I couldn’t solder directly to the frame, I drilled a small hole in the top of each frame half and then screwed a small screw into each. I then was able to solder to the screw head. In the picture, you can see the screw head on the left broke off, but I was still able to solder to it.
Wiring harness now soldered to the left and right frames.
There was enough space between the two frames sides to route the motor wires. So ran the wires down and around the motor as needed and then soldered them to the motor tabs.
A view of the wires going between the frame sides.
At this point, I was able to partially assemble the locomotive and see if it would work.
A view of the train connected to my DCC++ system and homemade throttle (more on this later).
I cut down the LED circuit board for the front LED.
Next, I removed the LED for the rear light and connected it to the back.
I used small strips of electrical tape to secure the various pieces in place. This is really just to keep everything in place while I slide on the shell.
Once everything was secured in place, I was able to slide the shell back on and the conversion is complete!