Bachmann N scale USRA 2-6-6-2

M1 decoder Installation

Text and Photos by Nicholas Camburako

The Bachmann Spectrum USRA 2-6-6-2 Articulated steam locomotive is one of Bachmann’s finest steam locomotives and probably their best N-scale locomotive. The installation has been simplified due in part to the locomotive being DCC ready, but some challenges arose which were not described in the trains included documentation. These areas are found through out the instructions, but can be quickly found by looking for the areas designated SPECIAL NOTE. This is a step-by-step write up on how you can perform the installation. As you follow the detailed instructions below, I will call out some sections of the Bachmann part designation as found in the included assembly diagram and parts list provided with the locomotive. This will assist in the locating of described areas.

This description describes placing the decoder in the locomotive were the power connections are located, in place of the boiler weight. Part numbers in brackets refer to the Bachmann assembly diagram and parts list included with the locomotive.

Step 1 – Remove the Tender Remove the tender from the locomotive by carefully splitting the wires apart and then prying the drawbar off the post with a small flat-head screwdriver.
Do any desired conversion of the tender's coupler to a Micro-Trains coupler (MT 2004) now. Set the tender aside until the decoder installation in the locomotive is complete.

Step 2 – Remove the Locomotive Shell Carefully placing the locomotive in your hand upside down, use one hand to hold the cab with your fingers and the other to hold the draw bar pin. Slowly wiggle the draw bar pin from the cab until they become loosened from each other. Once loosened, lift up the rear of the shell and slide it forward. Note that you do not have to remove the cab assembly or cab handrails. Place the shell aside until re-assembly later. The boiler weight (00N04) may lift up at the same time as the shell. If this happens the weight will keep the shell from sliding forward. Use a small flat-head screwdriver to pry the weight back down.

Step 3 – Remove the Locomotive Weight and Insulator Plate Remove the metal weight (00N04) from the boiler and set it aside. Also remove the insulator plate (0AC01) that sits beneath the weight and over the screw terminals. There is plenty of room to mount a decoder in this area.

Step 4 – Remove the Power Contacts from the Locomotive For the locomotive headlight and motor leads, be sure to have about 1/8” of the wire stripped back and tinned for making connection to the decoder. Remove the screws (SCREW-10172) that were under the insulator plate from the terminals, and then cut and/or unsolder the wires from the contact plates. Two of the contact plates will be used for the for the decoder power leads (red and black). The other two contact plates will not be used.

Step 5 – Prepare the Decoder for Installation To prepare the decoder for installation, the decoder wires need to be cut to length, stripped and tinned. This can be done a couple of ways. Because the boiler area has plenty of height, I chose to keep the wire length longer and just wrap it up to the decoder, which I then taped up. This gives me the options of possibly using the decoder elsewhere in future. The lengths I chose were as follows: White, Blue, Grey, Orange – 2 ½” long. Black, Red – 3” long. Yellow – 5” long. Fold up only 2” of each wire length and shrink-wrap or tape this excess wire to the decoder. The other option, and probably the simpler one, is to just cut the wires to the needed lengths, but be careful not to cut them to short. In both cases, once the wires are cut to length, strip about 1/8” of the wire back and tin the ends. Solder the red and black wires each to a contact plate that was set aside from Step 4.

Step 6 – Connect the Decoder Power Connect the power wires from the decoder to the locomotive by screwing the red wire contact plate to the right (engineers) side of the frame and screwing the black wire contact plate to the left side of the frame, in the same location were the screws where originally removed from.

Step 7 – Isolate the Decoder If using a decoder without shrink-wrap insulation, place a piece of Kapton Tape (or other insulating tape) over the screws. Make sure the tape goes up both sides of the cut out in the frame to insure the decoder cannot short out on the frame. Once the power contact plates are connected, push the decoder carefully into place over the screws. Do this gently as the wires on the decoder are very small and may break off if bent too tight.

Step 8 – Connect the Decoder Outputs Cut 4 pieces of shrink tube to about 5/16”. These will be used to insulate the remaining wire connections that need to be made. An alternative is to us Kapton or electrical tape. Place a piece of the cut shrink tube on each end of the wires from the locomotive before soldering.

Solder the following wires together:

Locomotive Decoder

Red White

Black Blue

Orange Grey

Brown Orange

SPECIAL NOTE: When connecting the wires for the motor per Bachmann’s suggestion, I ran into the problem of the locomotive running opposite of what it was supposed to (forward was reverse w/ light, and reverse was forward w/o light). The fix for this was to reverse the motor +/- leads as shown in the table.

SPECIAL NOTE: There are at least three ways of connecting the headlight for the locomotive, and they are as follows:

Method 1: Use the existing light board with the yellow LED unmodified. (Used for this installation)

Method 2: Replace the yellow LED in the existing light board with a Richmond Controls 3mm Golden-White LED. Use a soldering iron with a maximum 15 watts power. Remove the existing yellow LED. Carefully cut the leads and bend them at right angles to fit the golden white LED on the board with its leads going to the holes where the yellow LED was removed. Solder the LED to the board. Using a 9-volt battery, determine which wire is positive, and then connect that headlight wire to the decoder blue wire, and the other headlight wire to the decoder white wire.

Method 3: Instead of using the light board supplied with the locomotive, you can make a realistic-looking headlight with a Richmond Controls 3mm Golden-White LED. Solder a 560- or 680-ohm, 1/8 watt resistor close to one lead of the LED. This resistor fits nicely in the cavity where the light board was located. Using a 9-volt battery, determine which wire is positive, and then connect that headlight wire to the decoder blue wire, and the other headlight wire to the decoder white wire. When soldering the wires together, be sure to keep the connection joints over the decoder cavity.

Step 9 – Secure All Wire Lengths in Place Use Kapton Tape or other insulating tape to secure the wire just behind the light board and in front of the motor cavity in place.Use Kapton Tape or other insulating tape to secure the wire just behind the motor cavity and in front of the decoder cavity in place.Use Kapton Tape or other insulating tape to secure the wire splices in place over the decoder.Notice that the yellow wire can be seen going from the decoder to the front of the train. This wire was not connected. I chose to leave the wire length in the event that I’d want to use this at a later time. I ran it all the way up, just behind the light board, with no wire exposed to short to the frame.

Step 10 – Test the Locomotive SPECIAL NOTE: Before performing any track test, I recommend that you first check continuity to the rails for the existing light board supplied with the locomotive. I found that the small screws that hold the light board in place had to be removed at this point because they caused a short from the locomotive frame to the decoder through the blue and white light contacts on the decoder. Remove the screws if necessary.

Place the locomotive on the track with DCC going to it. Next, test the installation and be sure it works as it should using the default address of 03 for new decoders. The tender is not needed for this test, but make sure all the locomotive side rods and linkage are in place. If the locomotive does not perform as it should recheck all connections to the decoder and test again. Do not proceed until all problems are resolved.

Step 11 – Reassemble the Locomotive Next we reassemble the locomotive, essentially in the reverse sequence to its disassembly. Pay careful attention to the details on the locomotive. Finally re-attach the tender.

Step 12 – Program the Decoder Perform a test of the locomotive and tender on the railroad to ensure proper operation. 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 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.