# USAT SD40-2 Fix



## ewarhol (Mar 3, 2014)

So after placing brass tube sleeves on my axles to prevent the inevitable cracked axle issue, I began to have issues with the engine shorting out. This never occurred before the brass tubes were installed. Under the thread http://forums.mylargescale.com/39-dcc-large-scale/57762-usat-sd40-2-troubleshooting.html it was discovered that the brass rods inside of the trucks were shorting out on the new brass sleeves. I decided to remove the brass rods and hardwire the motor and wiper pickups. Follow along while I show you what I did.








This photo shows the original manufacturer wiring at the backside of the truck. The outer wires are for the motor, and the inner wires are for the wiper pickups. I used a tweezers to pull the outer wires out. They are clips that slide on/off of the brass rods. I placed a small amount of masking tape around the motor wires to help me keep track of which wire is for what. After that I then removed the pickup wires (which were not marked with tape). The next step is to remove the 12 screws (six per side) that hold the side frames on (I placed the screws and any removable parts in a tray so they don’t fall of the workbench). Then remove the screw that holds the front floppy wheel to the main motor assembly. Once this is done the motor assembly can be picked up and set on the workbench for further work.








Now remove the six screws that hold the top cover of the motor assembly on. Remove the wheels and the middle gear assembly. Set those aside in a tray so they don’t roll of the workbench. In this photo you can see the red wires attached to the brass rods. The outer rods are for the motor and the inner rods for the wiper picks ups. When the rods on the same side would come in contact with the brass sleeve, a short would occur.








Flip the motor over. Remove the six screws that hold the backside cover on. Place the screws in a tray. 








Once the back cover is removed the motor can be removed. Note the orientation of the red dot. This is the side where the red wire will hook up to. Make sure the red dot ends up back on the correct side. After the motor is removed the brass rod covers can be removed. Unsolder the red wires from the brass rods, and then the rods can be removed.








Here is what the motor block looks like with everything removed. 








The holes for the inner rods were too small for the diameter of wire I was using. I used a sharp scalpel to enlarge the holes. Don’t worry about the outer holes; wire will not be passing through those for the motor.








Because of the wire size, it did not fit into the slots the brass rods were in. I marked the wire where the coating needs to be removed. Using a wire stripper I gently cut the coating on the marks (make sure not to cut to hard or deep so the wire breaks). I then used the scalpel to remove the coating between the two points. 








Here is what the wire looks like after the section of coating has been removed, and the cover put back in place. Of course I realized at this point that the red pickup wiper wire was on the wrong side. Make sure to double check your work has you are moving along to keep things correct. Make sure to solder the wire to the pickup wiper tab on the top side of the motor block. 








Here is what the completed wire hookup looks like. Now the motor block can be reassembled in reverse.








Here is the completed motor block. I snipped off the clips and soldered the wires together. I used heat shrink tube to protect the connections. I worked one truck at a time. This way I knew I had one properly functioning motor. While the engine was upside down I hooked wire up to the wipers on the untouched motor block. I verified that the wheels on both motor blocks were turning the same direction. This tells me the wires for the motor are hooked up correct. If the wheels would have been spinning the other direction I could have dissembled everything to switch the motor wires around, or taken an easier route and switched the outer wires around. I used wire to connect the two set of wipers together to test that they were wired correctly. Once everything passed without shorting out I moved on to the other motor block.

When I originally installed the DCC decoder in this engine it bugged me that the red and black wire colors were mixed together to get things running correctly. This happens because the motor blocks are all wired the same at the manufacturer. When the rear truck is spun 180 degrees the colors don’t match up. The next engine I install a decoder into I’m going to set it up for Left Rail Black wires, Right Rail Red wires and keep everything consistent (i.e. only red wires will be joined together, and the same for black wires).


----------



## Greg Elmassian (Jan 3, 2008)

Eric, you are learning and I commend you for that.

I would monitor your changes carefully, and I have a number of questions.

These questions are not to "put you down" but to consider the long term results.

1. Did you use solid or flexible wire? It looks like solid.
2. What gauge wire did you use?
3. I would question wiring the blocks differently, what that does is remove the interchangeability of the blocks, which may affect you in future maintenance, and may confuse others if they get their hands on your stuff.

It seems that your main issue was clearance between your brass sleeves and the metal pins. I have not had that issue, so I will have to look at mine and see why.

Perhaps your tubing was too thick walled, or maybe the metal wires needed to be bent away.

In the end, congratulations for figuring out what the issue was, it was a bit tricky.

Greg


----------



## ewarhol (Mar 3, 2014)

Hey Greg-

1. I used solid wire, all I had in hand. I only brought it out far enough to soldier the manufacturer's flexible wire to it. If I were to run a line from the motor all the way to the decoder it would be flexible wire. 

2. It's either 18 or 20 gauge, whatever RadioShack had on hand. It's not stamped. 

3. I like running things through JMRI and WiThrottle. Under each engine's user file I leave comments in the misc./notes section of things I did with wiring, other weird hook ups, etc. 

I don't plan on selling my equipment, usually once I have something I keep it. If I do sell I'd tell the buyer what the misc./notes section says. 

No worries on "putting me down". We're all here to learn and share ideas. If I notice any failures with this I'll update the thread.


----------



## Greg Elmassian (Jan 3, 2008)

I think the solid wire was the right choice, flex wire won't stay put, and you had an interference issue. Also when you solder to flex wire, you can get breakage at the point the solder stops, it needs a strain relief and there's no place to do it in this instance.

Using solid instead of flex can seem counter intuitive sometimes.

Yeah, the JMRI data base is often overlooked by users, good choice.

Greg


----------



## ewarhol (Mar 3, 2014)

Ran the engine for about 3.5 hours on Sunday. Ran Great! The lubed up axle ends sure help. Used Lucas Oil Red N Tacky #2. Motors sounded nice and quiet, could barely hear them with the QSI sound well under 50%.


----------

