# USAT 70D Decoder Installation



## ImaGizmo (Jan 17, 2012)

I just purchased a new USAT 70D Locomotive and want to open it up to look at its inner workings.
I like to read up on Manufacturer instructions prior to turning any screws and doing any possible warranty voiding operations to equipment.
I have the SD70 User Manual which does not show how to open it up. And I have gone to the USAT web site looking for more detailed information.
I have searched the web looking for help on Decoder Installations in the SD70 and did not find any.
Turning the locomotive over (belley up) I see very small screws around the outer edge of the houseing and assume that removing the screws I should be able to separate the housing from the working parts.
Question: Is there any reference material available on line on how to install a decoder in the SD70?
What brand and model number decoder would you recommend?

Keep in mind I am brand new at DCC and the SD70 is my first step up from a DC Bachmann Starter Set.


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## Paul Norton (Jan 8, 2008)

I can't help with the decoder, but here is how to open the SD-70.

*OPENING THE CAB AND LONG HOOD*
Remove the four screws from the base of the fuel tank. Remove the fuel tank and set aside for now. Install the fuel tank screws back in the frame so they don't get lost. 









Under the cab there are two very small screws, highlighted in blue, in the side of the frame by the cab. A very small (2 or 2.4 mm) Phillips screwdriver will be required to remove them. 

*NOTE:* A six piece set of precision screwdrivers from The Source in Canada (stock number 640-1962) is $8, and from Radio Shack in the USA (stock number 64-2969) is $6. The 3.8 mm screwdriver is my most used tool for large scale train work. 









There are ten more screws, highlighted with yellow, holding the cab and hood to the frame. These are hidden in deep burrows in the frame and will require a long Phillips #1 screwdriver to remove them. 

*CAUTION* Do not remove the side frames or the motor blocks to access any of the screws, as the U-joint between the pivoting and main motor blocks may come undone. The U-joints can only be accessed by removing the top cover on the main motor block.
The first two screws are directly behind the front pilot.The next two are hidden under the front truck. These are the hardest to remove. The truck will have to be turned and the screwdriver inserted between the side frames and the motor block between the center and rear wheels. The wheels may have to be pushed against the motor block for clearance.Two are in the middle of the empty area left by the fuel tank.Two are behind the fuel tank, in front of the rear truck.The last two are under the rear, pivoting motor block.[/list] *CAUTION:* Do not lift the shell too far up or the front headlight wiring may unplug.
Turn the locomotive over. Carefully lift the shell from the rear. The long hood and cab will lift off as one piece.


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## Treeman (Jan 6, 2008)

DCC control of of all of the lights on this model will be a job. A down and dirty job can be easy. That is run the entire board from the motor output. The worst thing about this method is that when you stop the lights will go out.


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## ImaGizmo (Jan 17, 2012)

Thank you Paul and Mike for your replies. 
Paul your description and photos are exactly what I need to take the plunge and open this loco up. 
Going to print this out and take it out to the shop and get to work. I do have many of the small tools I need left over from my days of building and flying RC airplanes. 
The lights sound like they are going to take more reading time to figure out. 
I have found a decoder that looks like a good mate to the SD70. 
AirWire SD70 Drop-In DCC Decoder. Part Number: AWSD70. $129.89.


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## dawinter (Jan 2, 2008)

The 'drop-in' decoder is what I'm installing now. The SD70 is the guinea pig that will live or die on behalf of my regular fleet. Note: When/if your installing the Phoenix sound board be sure to ask for the special harness that's needed for the connection. Something I didn't know about and now I'm waiting with my engine all in pieces on my work bench. I expect it will work just fine (actually - I hope it will work just fine)


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## ImaGizmo (Jan 17, 2012)

Dave, 
Thank you for the Decoder and Sound Board Information. 
Please keep this topic up to date with your "drop-in" decoder progress. I would like to know any problems you may have with the installation. This will be my first Decoder installation and perhaps I may be taking to big a jump by starting with the SD70. 
Guess I am going to have to come up with a name for my layout to keep up with the big runners. 
Probably will be Volcano & Gold Creek Railway. 
Gordon


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## Treeman (Jan 6, 2008)

Do you know that Air Wire is intended for battery operation. It will handle the light functions well. You will need an Air Wire cab. I would suggest the T-5000.
It is not for track powered DCC, but a very good system.


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## Trains West (Oct 4, 2008)

what drop in decoder? usa is never drop in ........ the easyest down and dirty install is to cut the motor wires and power pickup wires from the usa board and put them to a decoder then useing the power in point to the usa board and power the whole board up with one fuction and a relay


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## ImaGizmo (Jan 17, 2012)

Mike, arent all decoders and the Air wire decoder NMRA standard and can be used with any NMRA complient DCC system? 
Also electronicaly wise (me being new and just manybe not knowing what I am talking about) I would think that the decoder would not be able to tell if it was getting its power from a battery or the track, as long as the input voltage to the decoder was the correct value???? 

Scott, could the USAT SD70 just possibly be built for drop in decoders? I wont know for sure myself until I open the loco up and take a peek at the insides. 

Gordon


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## Treeman (Jan 6, 2008)

Air Wire has build their drop ins specifically for certain USA locomotives. They are made to handle all motor and lighting functions, very nice. But they receive commands from a radio transmitter, not from track DCC. The decoder has a DCC output used to trigger sound on a Phoenix sound board. To me this is where they are different from something like the Revolution.


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## ImaGizmo (Jan 17, 2012)

Thanks Mike, 
Well another of many lessons learned that Not All Decoders are created equal and compatable to DCC. Guess I just missed out on the part where the Air Wire Decoder description left out saying it was NMRA. 
To me Batteries are a Royal PITA and I would rather clean track and wheels than deal with batteries. Also I have a friend that is staying with his Analog DC equipment and runs his trains on my layout, so I need my power blocks wired to handle switchable DC and DCC. That eliminates Air Wire for me. 
Sooo back to the search for a DCC NMRA Decoder for my USAT SD70. 
Gordon


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## Treeman (Jan 6, 2008)

One that has been recommended is NCE, that will handle 8 AMPS... Think about the down and dirty install, it would be quite easy. I am sure the light could be done properly with constant on but it would be a job. Is it necessary, that is up to you. Do you care if the lights go out when stopped. The NCE decoder does have a lot of light functions built in.


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## ImaGizmo (Jan 17, 2012)

Digging and digging on the web I found a good reference photo and instructions for the installation of the AirWire SD70 Drop in DCC Decoder. 
The photo in the article shows the SD70 cover off and the AirWire Decoder, Sound Board and Battery in place. 
So now I have some idea what the locomotive looks like with the cover off and a very good example of the decoder installation for the AirWire System. 

Yahoo, Bing or Google Search for CVP Products and find CVP Products Home Page. 
Click on: 
AirWire 900 Product Family 
Mobile Decoder 
Drop Ins


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## Greg Elmassian (Jan 3, 2008)

The AirWire system is not standard, signal and power from the rails DCC. 

It receives a MOSTLY DCC waveform over the air, but it is NOT 100% DCC, i.e. not all functions are exactly the same, especially programming functions. 

It would be interesting to see what you could do if you powered it from the rails, but you would have to rectify the track power and apply it to the battery inputs, and then find a way to supply the dcc signal into the board, since it accepts the "DCC like" signal on a 5 volt, unipolar input from the 900 MHz radio receiver. 

For beginner, I would not recommend this experiment. If you want to convert it "properly" see my pages on the USAT F3 on my site, under motive power... 

Also I recently used an NCE decoder to allow control of some more separate functions, especially the classification lights, it's in my DCC section, under NCE decoders. 

Regards, Greg


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## Trains West (Oct 4, 2008)

if you run power from the rails to an airwire system you will fry the board it is for battery only


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## ImaGizmo (Jan 17, 2012)

Greg, Thank you for the information. I have been to Greg's web site numerous times and find the site very helpfull and informative.


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## ImaGizmo (Jan 17, 2012)

Greg, Thank you for the information. I have been to Greg's web site numerous times and find the site very helpfull and informative. 
My bad. sorry for the duplication. in my impatience I hit Submit to many times.


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## ImaGizmo (Jan 17, 2012)

Scott, 
Here is a copy and paste from the CVP Products website. 

Can the decoder pick up power from the track? 

"This is not recommended or supported. But, yes it can be wired to do this. However, do not assume the batteries can be charged - lithium cells will not allow intermittent charging and doing so will damage the battery. However, 12 volt lead-acid gel cells can be used in this way. But, not only do you have to keep the track and wheels clean, but now you have to worry about electrical safety and reversing loops too. Thus, we don't recommend doing this since it negates all the advantages of battery operation." 

AirWire Power from the rails can be done.


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## dawinter (Jan 2, 2008)

Posted By Trains West on 19 Jan 2012 07:36 AM 
if you run power from the rails to an airwire system you will fry the board it is for battery only 
I'm going to run my 'drop-in from track power. I know it works just fine because many people have done it successfully.  I have installed a full wave bridge between my track power supply and the i/p to the board (battery i/p) and set the track power to about 16 volts. The drop-in always gets the required +/- polarity regardless of track polarity.

As I pointed out earlier, I'm waiting for a correct drop-in/Phoenix connection, but the Airwire components work just fine using the bridge. Also remember that the front and rear truck 'pick-ups' are reversed as far as I can tell. Something to think about when connecting them together and making your final connection to the battery i/p.

Comments please if anyone sees an issue I'm missing.


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## ImaGizmo (Jan 17, 2012)

Dave, Sounds like you are getting close to wheels turning. 

This is just my curiosity speaking out and obviously not any great knowledge of electronics. 

But what if? you connected a small Battery Charger to the Tracks in lieu of a Power Supply? Something along the line of a 12V charger used for auto batteries. I believe a 12V Lead Acid type Battery charger puts out something in the neighberhood of 14V to charge an auto battery. You would have 14 +/- volts on the rails all the time from the charger. 

Possibly install a small capacity Sealed Lead-Acid Gel Cell in the locomotive and connect it to the track pick ups to act as a buffer between the Battery Charger and the Decoder. The battery would stay fully charged and would make up for any small intermittent opens or voltage fluctuations that will occur due to dirty tracks and wheels. 

I don't know how a Decoder would handle a series of on/off/on/off/on voltage fluctuations from the tracks without a buffer like a battery or capacitors to keep the voltage on all the time???? 

Gordon


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## Greg Elmassian (Jan 3, 2008)

There's been quite a few threads over the years about this. 

The bottom line is that the best you will come up with it extending the run time somewhat, but not recharging the batteries. 

Here's some info to help you understand this: 

If you use a "dumb" charger, you basically put a fixed voltage on the rails that is appropriate to charge the battery. 
What is wrong with this is that it will charge too slowly to be of any use, unless you raise the voltage, and then it will over charge. 
Also, every battery is somewhat different, so different batteries will charge differently. 
Now, put a second loco on the track and you have an even less controlled system. 
It just does not work. 

The next idea people come up with is a smart charger, that senses the condition of the battery and charges it. 
All well and good if you NEVER interrupt the charger, which can reset the charge cycle and lead to fatal overcharging. 
Again, won't work for multiple locos. 
Also, the varying load on the battery from running the loco will confuse the charger. 

OK, so the next idea that people progress to is to put some lower voltage on the rails, so overcharging is not possible. 
So for example, you run 18v batteries, but you put 16v on the rails, sounds logical, right? 
Except now, your locos rapidly discharge to 16v, and then depend on the track voltage to run. 

Bottom line, you gain nothing except the extra expense of batteries, installation, more electronics and chargers. 

I hope this BRIEF explanation helps put it into perspective. 

Regards, Greg


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## ImaGizmo (Jan 17, 2012)

Greg, 
Thanks for all of the good infomation in your posts. It seems batteries are a catch 22 when it comes to train power. Darned if you do and darned if you don't. Very hard to extend run time without changing to fresh batteries or stopping for a re-charge. 
Supprised nobody thru this brain storm at you yet. Put 2 batteries in parallel which would increase the AmpHours. Of course this would increase total engine weight which would decrease the number of cars the engine could pull. 
The handwritting on the wall as far as batteries go is there is no good solution to increase the battery driven run time except what has so far been tried and proven to work best. 
New people like me are always trying to re-create the wheel when it has already been tried by so many others. 
But I guess why we have the "Beginner's Forum" for us to learn from. 
Sorry I pulled this topic away from the SD70 Decoders and started on to Batteries and track power. 

Thanks 
Gordon


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## Greg Elmassian (Jan 3, 2008)

It's ok, this question has been asked many times. Yes, longer run times take more battery amp-hours (besides the obvious run slower, no extra lights, no smoke, no sound). 

Beginners forum is anything goes and no question is wrong to ask, glad to have you aboard! 

Greg


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