This installation documentation is for the HO Scale Bachmann GE 70-Tonner. This installation shows the installation process of the early frame design which features dual motors. The 70-Tonner from Bachmann was redesigned more recently to a single-motor design and is more DCC-friendly. Use this documentation only if you have the first-generation model with the dual-motor configuration. This installation uses the WOW121-Deisel decoder, 21-Pin Junction Board, 35mm x 16mm Oval Speaker, and KA4. This installation was performed by TCS' Dan M.
The Bachmann GE 70-Tonner shown prior to installation.
To remove the shell, we first need to take off the fuel tank that is held on by the single scew highlighted in red.
Once the fuel tank has been removed, take out the two screws that hold the shell onto the chassis.
Once the shell has been lifted off, the DC board can be removed by taking out the screw highlighted in red.
With the screw removed, the DC board is now free. You can clip off or de-solder the wires in order to tak th board out completely. We will be re-using the original lights in this model, so we de-soldered them and set both lights aside.
After removing each of the screws which hold the trucks in place, the trucks can be taken off. The chassis can be set aside for now. NOTE: The process below needs to be done for both trucks individually.
We need to insulate and add new wires to the motors, which means the trucks must be disassembled. To start this process, loosen all four screws highlighted in red.
With the screws loose, pop off the top of the truck and remove the motor.
The pickups that are indicated in this photo should be clipped off to prevent shorts to the motor from the track power.
Shown here is the truck with the power pickups properly clipped.
Now that the motor has been removed from the truck, we can add our wires that will be run to the decoder. It is important to keep in mind that one motor will be running forwards, and the other motor will be running backwards in order to have the locomotive travel in one direction.
Wire the motors to correspond to the direction they will need to travel. You can test the polarity of each motor by connecting it to a DC power supply, or temporarily to the decoder. Make sure that you wire the motors such that they both spin the wheels of the trucks in the same direction.
Once your wires have been soldered and you are sure that both motors will work with each other, wrap both contacts in electrical tpae as shown above. Note that it is important that the tape be taught, otherwise it can get stuck to the armature of the motor and prevent it from spinning.
You can now re-assemble the truck and motor. You will also at this time need to add the track power pickups which will go from the trucks to the decoder. Note that on this truck the Left Rail (Black) has been indicated.
For the most convenience, we recommend routing the wires exactly as shown so that they do not get tangled and can be easily routed up through the frame.
Shown here is the other truck, fully assembled. Note that the track power pickup is now on the opposite pickup, but will be on the same side of the locomotive, meaning it will conduct from the same rail.
The 21-pin junction board may now be adheared to the chassis. You may use double-sided tape, hot glue, or other adheasives to attach it. Note that the wires from each truck have been routed through the chassis and have been trimmed so that there is enoguh wire left to allow the trucks to rotate.
On each light, a short section of wire was added. Since these are 12V light bulbs, the polarity does not matter, but we used colored wire for easy recognition.
The lights, motor, track power, and Keep Alive are now connected. We wrapped the Keep Alive in black electrical tape so that it would not be as obviously seen through the cab windows. It will be visible, but the tape gives it an ambiguous shape and color so it is not easily recognizable.
Shown here is the speaker with wires soldered on correctly and ready for installation.
Once the spekaer has been wired into the junction board, the decoder may be seated on top as shown here.
In order to fit the shell back on, it may be necessary to remove these two clips. These serve no purpose, as the cab is typically glued in place from the factory. We found that by using a small pair of needle-nose pliers you can wiggle these tabs and break them off. Once you have done this, carefully replace the shell onto the chassis, Your engineer can still fit even with the Keep Alive in the cab if you are careful. Once the shell is in place, replace the screws and put the fuel tank back on.
Important Soldering Tip
Please do not use any flux either liquid or paste on the mother board. Over time, the acidic properties of liquid or paste flux will begin eating away at the fiberglass PCB and will damage it. Use only Rosin-core solder or no-clean flux approved for electronics use.
TCS recommends the use of Kester "44" Sn63 Pb37, .015" diameter Rosin-core solder. Kester part number 24-6337-0007.
You can order this solder from the following retailers:
Digikey - PN:KE1110-ND
Techni-Tool - PN:488SO6775
Other solder tips
When stripping wire, only strip a tiny little bit of the insulation. Strip no more then a 1/64 of an inch. When the wire gets tinned with solder, the insulation will shrink back more. Try to not expose any more wire then half the length of the solder pad at most. In no case should solder or exposed wire wire ever be outside the boundary of the the solder pad you are attaching a wire to.
Click here for important information on properly Stripping and Tinning wire