USAT DCC installation techniques

Overview

USAT locos are not traditionally thought of as "DCC friendly".

In truth there is a way to add DCC (or any system) from really easily and painlessly.

A full conversion, getting more features, take a little more effort.

"quick and dirty" conversion - simple, cheap, using stock wiring

•  pros: inexpensive, easy, no soldering, simple to return to stock
• cons: lights and smoke will not stay on when the engine is stopped, sound like normal DCC install

"full conversion" - rewire & get control of all the lights and smoke units

• pros: lets you really control all the lights independently and get the classification lights to work right with the right colors. Smoke unit can throttle up and down with diesel notching. Can be done after the "quick and dirty"
• cons: can be a bit of work and basically rip out the incandescent bulbs from older units and put in leds for most lighting, need more wires and connectors.

for now, reference the USAT F3 pages, the main F3 page and the F3 DCC install.

Quick and Dirty install

The basic idea is to route the power:

• from the track into the decoder track inputs

• from the decoder motor output to the original track input on the USAT boards.

Thus, you are running the entire loco on the decoder motor output, i.e. lights and motors and smoke. (clearly the sound is directly from the decoder)

Typically, USAT locos have 2 "sets" of wires with connectors coming from EACH truck, and they use the familiar 2 pole "JST" style connector. The picture below shows on set from one truck, this one is an NW-2.

The connectors that USA Trains uses are the same kind that Aristo Craft used for the "mu" connection between loco.

The connectors come in many configurations, with all with a 2.5mm pin spacing.

Just above, the male is on the left (see the pins), and the female is on the right.

So, going back to the picture above, if you look closely, you will see that the "sex" of the 2 wires coming from the truck is different between the motor and track wires.

On the truck side, the male connector at top, with the 4 wires is the track pickup.

Again, referencing the truck side, the female connector with 2 wires is the motor connection.

If you pay attention to this, it will become almost impossible to mess things up.

 IMPORTANT: you need to VERIFY what is said here with an ohmmeter. This will be part of the instructions, but do NOT be tempted to just follow the pictures!

Don't go nuts and start unplugging everything, or go out of order.

Track Pickup wiring - get power to the decoder

As already identified, the male connector with the 4 wires are the track pickup wires. Disconnect these, one set at each truck. LEAVE THE OTHER CONNECTORS ALONE. (This is the mistake everyone seems to do).

Now get two female connectors with nice long "tails". The connectors should look like this:

Now you need to do something that may not make sense. Take the 2 connectors and take the red wire from one connector and twist it to the black wire of the other connector. Do the same for the remaining 2 free wires. Seems nuts, but you have to remember that the trucks are identical BUT they are pointing in the opposite directions on the loco. So what is the left pickup on one truck is the right on the other. Trust me. So, if the left pickup is red on the front truck, the left pickup on the rear truck is black.

Now you plug these 2 cables into your 2 trucks and you have your power pickups.

To do DCC correctly, you also want to determine which wire is left and which is right. Take out the ohmeter, put a probe on one of the wheels, and see which wire it is. You can determine which of the red/black pairs is the right rail pickup and which is the left rail. Right and left will be identified on your decoder.

It's a good idea to double check that ALL the wheels on one "side" of the loco are connected.

"Motor" wiring, i.e. power the loco "guts" from the decoder

Now we are going to feed the decoder motor output to the entire loco, via the main board. (normally it would go to the motor only)

When you unplugged the 2 connectors from the main board, you "filled" the truck sides, but you have 2 remaining "loose" connectors, both of which go to the main circuit board.

Take a SINGLE male connector:

and connect it to the MOTOR + and the MOTOR - leads on the decoder, (by convention these are the orange and gray wires on a wired decoder).

Now plug the connector into EITHER of the 2 "loose" connectors on the original USAT "main board".

Don't worry about which one, the process to determine it is too tricky for this level of install. You have a 50% chance of getting the polarity right, i.e. either it will go in the right direction or the wrong direction.

Now the loco should run on DCC.

If the loco runs backwards, then remove the single connector that goes from the decoder to the original USAT main circuit board (the motor outputs on the decoder) and plug it into the other "free" connector. (again since the motor blocks are identical, but physically reversed, the front and rear connectors are "reverse polarity" in respect to each other).

Now the loco should run the right way on DCC.

Final notes:

If you are running on DC also, and the loco runs in the wrong direction, you need to swap BOTH the motor leads and the track leads.

Swapping the motor leads reverses the direction for both DC and DCC

Swapping the track leads reverses the direction for only DC.

(think about it, it will make sense)