Eliminate fan noise on Dish 6000 w/ 8 VSB module installed...

Discussion in 'Archived Threads 2001-2004' started by Clay Autery, Sep 12, 2002.

  1. Clay Autery

    Clay Autery Stunt Coordinator

    Oct 23, 2000
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    If you have one, you KNOW what I mean! ;)
    The little Sunon fan in the 8VSB module is LOUD... I couldn't take the high pitched whine anynore, so I decided to disassemble the case and pull the module to see what could be done...
    I didn't want to insert a resistor to slow the fan, cause hey... it doesn't pump much air at full speed...
    Some investigation revealed that the vast majority of the annoying sound is due to 1) the fan is directly coupled to the module cover which is very thin sheet metal and has a simple friction fit over the module (for the most part anyway). At least they used nylon screws and nuts... BUT, these are typically glued shut with CA glue, so they will likely twist off if/when you try to remove them.
    Here's what I did:
    I bought some new nylon screws about 1/8" longer than the stock ones...
    Then I dug through my junk box and pulled out a spare piece of Sorbothane (http://www.sorbothane.com). This piece just happened to be an old isolation disc for use on a piece of industrial woodworking equipment, so it already had the approximate arc that was needed.
    I cut two arcs sufficient to cover the corners of two of the fan mounts and 1/8" (nominal) thick. You can't get much thicker or the screws that would be necessary might contact the PCB...
    I used a small drill bit by hand to drill an UNDERSIZED hole in the sorbothane... The undersized hole allows you to control the orientation of the screw in relation to the fan mounting holes... If possible, you don't want he screws to contact the sides of the holes... Takes a bit of trial and error, but you can do it...
    Now, the screw heads will still be in contact with the cover, but you can't help that... If you put a sorbothane gasket on top, you can't slide the module into the slot... BUT, you can put a thin gasket between the fan and the nut if you are patient... That isolates the fan completely from the screw/nut (providing the screws don't contact the sides of the fan mounting holes in the fan housing). (That's why you only use two screws... make it easier to avoid frame contact.)
    Now, with the fan re-mounted, I bent the sides of the module cover together some to make the friction fit tighter... tighter fit, less rattle due to vibration.
    Then I re-installed the module with the top cover off and plugged it in (BE CAREFUL that you don't electrocute yourself!!). I listened to the fan and the sound was drastically reduced. The Sorbothane gaskets absorb the vibrations (turn them into heat). The fan produces just as much vibration... you simply attenuate the audible noise...
    There was still some whine left, so I began "probing" different parts of the frame, module etc. until I found the culprit... It appears that the residual vibration sets up some harmonic resonance with the top panel of the module cover...
    So I cut the disc in half (height wise) to get a shorter cylinder (about 3/8" tall). Laying the disc on the cover killed virtually all of the remaining audible noise (except for the air movement). All the resonant freqs are gone... I moved the disc around until I got the best results (rear left corner of the module frame opening above the module as you view it from the rear).
    The disc covered some of the fan opening in this position, so I cut a relief to clearance the fan intake... The disc height is just taller (1/16" or so) than the top edge of the rear panel... this will allow the top panel to provide just a bit of compression on the Sorbothane disc on the module top cover...
    I re-installed the top cover, and the fan was inaudible at just over 12"..... nothing.
    I put the unit back in my rack and fired it up... From my seating position, you can no longer hear ANYTHING from the receiver... and that fan runs constantly regardless of the power state of the receiver.... if it is plugged in, the fan runs...
    Well, that's it... sorry no pics... I'm not taking that thing apart again... ;)
  2. Gregg Loewen

    Gregg Loewen Video Standards Instructor, THX Ltd.

    Nov 9, 1999
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    New England
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    Gregg Loewen
    Totally awesome!!!

    Im going to save this one to the HW Archives


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