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Thread: Atlas Master Line SD7

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    Default Atlas Master Line SD7

    I purchased 2 new SD7's (probably old stock from last run) and installed a Digitrax drop in decoder in one. It runs a maximum 40 smph in reverse and 25 smph in forward.
    I changed the cv's for top, mid, and start with no effect.
    Is this normal?
    My GP7's and 9"s run much faster.
    Any suggestions?

    Thanks,

    Harold
    HAROLDN212

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    that does seem a bit slow.

    causes can be hard ware decoder failure, low DCC voltage, binding in the loco, a motor failure of some sort, and perhaps an odd software issue.

    factory reset of the decoder should eliminate odd software...
    and then you can look at the decoder may have a hardware issue.

    so check the voltage at the track... I know if your other locos are faster you will still have the problem.

    so at this point fixing is going to involve taking things apart.

    since I think your motor and drive-train have a problem you will get here fairly quickly.
    look for all the usual suspects, lint, rocks, and gremlins.
    test the motor, I clean the commutator and then check for continuity with an ohm meter.
    even across the poles and no contact to the motor shaft.

    test the loco without the decoder if at all possible.

    from your description, not normal.

    victor

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    I disassembled the loco, the motor runs ok on dc. I have no way to know if the RPM is correct. I found no evidence of drive line binding or weak contacts. So I carefully reassembled it with no joy.
    I bought 2 of these locos new at the same time so I installed the same type of decoder in the other loco and it runs away from the first. Next, I will swap the decoders.
    HAROLDN212

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    Couple of ideas for narrowing it down:
    Reset the decoder to factory settings.
    Put the old light board back and see how it runs on DC.

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    I would reexamine the drive train. These are notorious for the plastic parts cracking and or otherwise slipping on the motor shaft. I had a similar issue with a pair of new old stock units. I ended up replacing the couplings between the motor and worm. And for a little extra security -- I used some CA on the parts. For mine -- it made a huge difference. On the surface, it sounds like your issue is drive train slippage.

    Wolf

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    Quote Originally Posted by SP-Wolf View Post
    I would reexamine the drive train. These are notorious for the plastic parts cracking and or otherwise slipping on the motor shaft. I had a similar issue with a pair of new old stock units. I ended up replacing the couplings between the motor and worm. And for a little extra security -- I used some CA on the parts. For mine -- it made a huge difference. On the surface, it sounds like your issue is drive train slippage.

    Wolf
    As stated I have 2, I swapped the driver trucks with no improvement. I'm down to the drive worm shafts next.
    HAROLDN212

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    Quote Originally Posted by NtheBasement View Post
    Put the old light board back and see how it runs on DC.
    I ran it with the DC light board but they don't run the same on a DCC layout. It is hard to compare.
    HAROLDN212

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    Quote Originally Posted by Papahnash View Post
    As stated I have 2, I swapped the driver trucks with no improvement. I'm down to the drive worm shafts next.

    Understood -- check the male universal at the motor shaft. One or both may have cracked.

    http://download.atlasrr.com/pdf/Part...s/NSD7Loco.pdf


    Wolf

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    I did not find any cracks in the drive shafts. I decided to go ahead and speed match the two starting at the top end. When I got to mid range they were near the same setting as was the low speed.
    I'm going to run them and look for any change.
    Thanks all for the info.
    HAROLDN212

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    You said that the speed didn't change when you changed the CV's for start, mid, and top. Could the decoder be set to use the 28 step speed table and not the basic speed table?
    You also mention that your GP 7's and 9's run much faster. Depending on when they were made, they could have an older high speed motor in them.

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    is atlas still using grey for the 'scale-speed' motors?

    I had read that the newer locos have black motors now.

    victor

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    Quote Originally Posted by bman View Post
    You said that the speed didn't change when you changed the CV's for start, mid, and top. Could the decoder be set to use the 28 step speed table and not the basic speed table?
    What I meant was that when I finished speed matching, the mid and low range settings were close to the same on the basic speed table.
    HAROLDN212

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    Quote Originally Posted by victor miranda View Post
    is atlas still using grey for the 'scale-speed' motors?

    I had read that the newer locos have black motors now.

    victor
    The motors in these are black. The date of manufacture on the frame is 2003.
    HAROLDN212

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    Quote Originally Posted by Papahnash View Post
    The date of manufacture on the frame is 2003.
    That's when that particular chassis first came out, but not necessarily when your loco was made. They don't change the date stamp with each new production run.

    -Mark

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    I have a similar unit, I think it's a GP40 without going to look, but with an Atlas factory decoder. On my speedometer full tilt on DCC is about 60 SMPH. It runs very slow across the board. I'd like to say slow speed performance was good as a result....but it is not.
    --
    Leo Bicknell

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    I do decoder installations for NE Ohio. Your decoder you have needs sent back. I had this happen multiple times with digitrax even after a reset. It can short out or have a capacitor have a solder break in transport from the factory. They have the no worries warranty. There is nothing wrong with the motor if it is fine in DC. It should only take a week or 2 to get a replacement.

    Ryan

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