USAT DCC installation techniques


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

In truth there several ways to add DCC from really easily and painlessly, to more effort, but getting more features.

I'll present 3 ways:

"quick and dirty" - 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

TrainTek Adapt-A-Board - a custom drop-in set of main board and light board(s)

  •  pros: replaces stock main board and light boards, no soldering, moderate level of effort to change out light boards. Has socket for decoders meeting the "aristo" standard, best with a QSI Titan
  • cons: moderately expensive ($90), you lose all of the original motor, sound, light switches, only have a smoke on/off switch, lighting boards do not handle red/green class lights (need to get confirmation from TrainTek).

"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 and put in leds for most lighting, need more wires and connectors.

I will put the "Quick & Dirty" and the TrainTek information on this page, but the "full conversion" install needs it's own page, and even then some specifics on each of the locomotive model pages.

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.

Typically, USAT locos have 2 "sets" of wires 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.



 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!

Track Pickup wiring - power to the decoder

First, we want to locate the connectors that have the track power pickup. USAT locos normally use more wires from the truck for power pickup.

Look at the upper connector in the picture above, there are 4 wires on the left side. That is the track pickup side. Separate these connectors at each end of the loco. (leave the others alone to avoid confusion).

Now you want to put a new connector and pigtail on each of the TWO connectors that go BACK to the trucks. Don't worry about the other 2 connectors that are attached to the circuit board at this time.

Since the trucks are identical, you will now do something that seems strange, but hang in there:

With your "new" connectors attached to the connectors from the trucks, you have 4 loose wire ends, 2 from each connector you just attached. Twist the red of one to the black of the other. Yes, twist the unlike wires together, the black from the front truck to the red of the rear truck. The red from the front truck to the black of the rear truck.

You now have 2 wire "sets", and each is 2 wires twisted together. Each set has a red and a black wire. (the reason is that since each truck is wired identically, but they are installed physically reversed from each other, then so is the "polarity" of the red and black wires)

Now we need to determine which of the 2 sets of wires is the right (or engineer side) wheels and which is the left side.

Get out an ohmmeter, and test it to be sure it indicates 0 ohms when you touch the 2 probes together. Don't go further until you can test and see that it's working.

Now connect one probe (does not matter which one) to one of your 2 wire "sets", and then test ALL the wheels on one side of the loco, and then the other.

One or the other side should respond. Be sure to double check ALL the wheels. One side should all be zero ohms, the other side should all be infinite resistance (open).

Now you will know which of the 2 sets is left and which one is right. It helps to tag them.

Once you have this tested, then connect the left and right wires to your decoder. The engineer side is called the track + or red wire on the decoder. The firemans side is called track - or the black wire on the decoder.

Test the other wire to be sure it is connected to all the wheels on the other side of the loco, and connect it to the decoder, on the other track pickup input on the decoder. (Yes, I know you already tested them, do it again to be sure)

At this time you have connected the track pickups to the decoder, both front and rear truck, and have correctly identified the right and left track pickups to the decoder.

"Motor" wirking, 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)

Take another JST and plug it into EITHER of the 2 remaining "loose" connectors (both go to the main circuit board), and connect the 2 wires from that connector into the MOTOR + and the MOTOR - leads on the decoder, (by convention these are the orange and gray wires on a wired decoder). 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 that connector that goes 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).

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)


TrainTek "Adapt-A-Board" USAT boards

There are a series of boards, but strangely, there is no board for the most sold USAT loco, the F3. Below is the next most popular, the current top seller, the GP7/9.

Notice the place for the socket, and midway on the board, 2 small thin sockets, you can see "rear lights" on the right hand one. This is a proprietary connector for his light boards and uses a thin, flex cable.

One thing I don't like is losing all the slide switches for motor, lights, sound, etc... the only slide switch "preserved" is the smoke switch. I don't see any reason the rest of the switches had to go, it would have been easy to put a switch for the motors, and probably disconnect the common for the lights.

Note on the right and left sides are little connectors that say "front lights" and "rear lights". You need a thin flex cable to go into these sockets, so you are basically forced to buy the LED or rewire yourself. I have not any pictures of the LED kit, or any knowledge on how it fits or how hard to install. 

Another big downside, is that this board REQUIRES you replace all lighting with LEDs, and they sell a LED kit. The board alone is $40 and with the LED kit it is $90.

Weather Underground PWS KCACARLS78