SWMLine LNB failure

Discussion in 'DIRECTV - SWMLine Discussion (private)' started by veryoldschool, May 13, 2008.

  1. Mike Bertelson

    Mike Bertelson 6EQUJ5 WOW! Staff Member Super Moderator DBSTalk Club

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    Hypothetically, if I knew all the pieces, angles, temperature extremes, I can determine all on loads on the connections...including the wind load on the dish.

    Hypothetically....

    Mike
     
  2. smiddy

    smiddy Tain't ogre til its ogre

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    I suspect, with a certain margin of error. ;)
     
  3. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Well long before you spend any time, I'd send you a photo and some scale, but right now I've changed from an aluminum pop rivet to steel and "soon" I'll add more [now that I know it "can fail"].
    I spent "my thoughts" on vertical loading and never thought the rotation loading would amount to anything. :lol: or is it :eek2:
     
  4. smiddy

    smiddy Tain't ogre til its ogre

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    It's those orthogonal issues that we forget about as tron folks. The Mechinized consider these...loads and compression and pressure. :) It sounds liek you have it in hand though now. Do you have an extra PI?
     
  5. azarby

    azarby Hall Of Fame

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    VOS

    Just to make sure I understand the fix, all of the LNB's are ok and it was just a rotational problem with the mount? I'm glad you got it fixed and it is a lesson for all of us, don't over look anything. It's a lesson I try to keep drilling into these younger hot shot engineers.

    Bob
     
  6. Mike Bertelson

    Mike Bertelson 6EQUJ5 WOW! Staff Member Super Moderator DBSTalk Club

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    Good thing you went to steel. Galvanic Couple....Dissimilar metals in contact.

    Although the anodic index for carbon steel and aluminum are very close, if the steel is galvanized(zinc coated) that gives you a higher difference in anodic index then you should have for outdoor use.

    Zinc is about 1.25, Al about .9 and the max difference you want for outdoors is about .15 (mild steel is about .8 - .85).

    The higher index gives up electrons to the lower. That's why zinc annodes are used on ship hulls. The zinc corrodes and the hull doesn't. In this case the zinc gives up electrons the Al and it becomes brittle.

    A steel rivet will nearly eliminate the galvanic couple.

    In an ideal situation, a tight rivet connecting two members will see only shear loading.

    In reality it is combination of axial and shear loading with a small component in bending. With one fastener(rivet/bolt/screw), it has to take all the cyclic loads. That makes it even more susceptible to fatigue.

    Mike
     
  7. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Bob,
    I didn't "think" I was over looking anything [and I ain't no kid :lol: ].
    This morning "I figured" the cement to steel contact had given way, so now I have a 60 lbs bag.
    How many of us have been working on a test setup that we can't get to work and had someone walk up and hit the power switch on a box that "we missed"?
    I'm normally the one that finds it, but lesson here: nobody is "superman".
    All LNBs have been tested and working fine. [well my AT-9 is still a guess but "five out of six" are known good so..... :D ]
     
  8. RobertE

    RobertE Active Member

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    ah, the good ole operator error. :lol:
     
  9. NR4P

    NR4P Dad

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    VOS, if its permissible and with a small amount of beggin, I'd gladly help you remove some of those cardboard boxes and take a SWM-LNB assembly as a spare. Even pay for the shipping too.

    Between summer lightning and hurricane season starts in a week, sooner or later, mine could go bye-bye.
     
  10. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    All of my "spares" are Slimline.
    [must keep on the installers to bring me my "spare" SWMLine since it was on the work order]. :D
     

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