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NW-2 Cow & Calf
Overall:
Thankfully, there are no traction tires on the wheels. I will probably remove the sliders and see if they still run well. Have not tried the smoke units yet. I think they could stand a bit more weight. I have a cow and a calf so far. Many railroads use a cow and one or more calves.
Nice level of detail, and the typical tradeoff, nice small details, but easily broken, note: the small plastic loops for the coupler cut bars are easily broken.
In order to change the headlight bulbs in the NW-2 you have to remove the headlight lens which can be difficult to remove.The railings press into little plastic cups that are glued to the frame with small, fragile pins on the bottom.These are easy to break off.
Kadee Couplers:
I trim off the tang, leaving about 1/16" of the thinner tang projecting from the thicker part. This allows you to use the existing hole that held the hook and loop. You can use the screw from the hook and loop. This is for 831 couplers.
Kadee also recommends cutting 5/8" off the tang, and you also need to cut 7/16" off the gearbox shank, and trim a slot in the lid 11/32" wide and 5/32" deep to match the sides of the pivot arm. This will allow closer coupling, and should work on curves under 8 foot diameter.
For larger curves, over 8 foot diameter, you can use the 787. I have not tried this yet, to see if it gives close coupling.
Disassembly:
First there are 8 screws to remove from underneath. As with many USAT diesels, some are best accessed with a slim philips head screwdriver between the sideframe and the motor block, after twisting the block into the best location.
First remove the 2 deep set screws where the 2 red straws are, they are easy to reach.
Now remove the 2 deep set screws at the front of the loco, the leftmost 2 in this pictures. By turning the truck to align with the screw holes you can reach between the motor block and the sideframes.
Now for the final 4 screws. These are in the approximate location of the middle set of 2 straws. There are actually 2 screws near each other on either side of the loco centerline. Two screws are deepset and they attach to the body. There are also 2 smaller, short machine screws. These attach to a metal bracket that holds the front of the cab down. These smaller screws are not deep set, and have machine threads. They are quite short.
The front of the loco has a tab that engages the chassis, so carefully lift up from the cab, not the front end and as you swing it up, the tab in the chassis in the front will disengage.
Wiring variations:
It appears there are 2 variations, an early version and a later version.
The difference seems to be in how the trucks are connected to the circuit boards.
In both cases, there are 6 wires from each truck, 2 for the motor, and 4 for track pickups (2 internal to the motor block and 2 picking up from the ends of the axles / journals)
Early version: (picture courtesy Dan Perrott)
In the picture above, the motor wires are at J5 and J6. The track pickups are at J4 and J5, the red and black wires. Unfortunately, to remove the truck you have to unsolder 4 wires, 2 of the wires are in the black JST-style connector at the top left.
Later version:
In the picture above, the track pickups are red and black, and go to the connector at top. USAT consolidated all 4 wires into one connector. The connector below is the motor leads. Easier to disconnect, but why use the same color for motor and track pickups? Oh well.
There are probably more variations in in the other wiring, will update this page as I go
DCC Install:
Let's start with what I call the "quick and dirty" installation. This is where you feed the track pickups as usual to the decoder, but then use the decoder motor output to basically feed the entire loco like it was on DC.
As I have mentioned elsewhere, this is very easy and quick to do, but has the disadvantages that you don't have constant lighting. Also, running the smoke unit might overload the decoder output. Finally, some locomotives have voltage regulation circuits for lights that go absolutely nuts when powered by PWM (pulse width modulation), especially Aristo ones. So we will try this first and see how it goes.
In the case of the NW-2 later type, we have a simplification that makes it easy.
Look at the wires/connectors from the truck. Each truck has 2 connectors, but there is a difference. One of the 2 connectors has 4 wires in it, 2 red and 2 black… the other connector has just one red and one black.
The connectors with the 4 wires is the power pickup from the wheels. This is because there is an internal wire touching the axle, as well as a wire on the journal where the axle tip touches.
So step A is to disconnect only the connectors that have 4 wires (this is one for each truck)… now take your con240’s and connect one to each “loose” wire from the truck. Now you have to realize that USAT uses two identical trucks.
And you have to realize that they are “reversed” from each other. So on one truck the red wire is the right rail, and the red wire is the left rail on the other truck.
So you have 2 CON 240 connectors plugged in. take their wires and connect red to black, and black to red. Strip the ends and twist the wires together. Now you just have 2 free wires, each is a red and black twisted together.
Now is the time to get out our ohmmeter. Connect it to one of the pairs, and check all the wheels on the loco. You should have all the wheels on one side.
Test the other pair. Put a little piece of tape identifying each lead as “right side” or “left side”. Now you have the track pickup leads ready to connect to the decoder.
Once you have done this, now hook up ONE con240 connector to either connector that was disconnected (notice that we never disconnect the motor leads)
These 2 wires go to the “motor” output of the decoder. Don’t worry about the polarity. Connect them and if the loco runs backwards, then you switch these leads.
I need to emphasize again that you ONLY disconnect the 2 connectors that have 4 wires in them on one side.
Speaker:
The speaker enclosure is under the loco and is held with 4 screws. It is "keyed" so that it can only go back on one way. The space inside is 1-1/8 inches deep. There is a circular relief inside the bottom that is 2.65" in diameter. You should pick a speaker with no mounting flange, but I have often sanded off the mounting flanges on a disk sander to accomplish this.