Thunderbolt iMac Projector Interference

Discussion in 'iMac' started by Starflyer, Sep 27, 2011.

  1. Starflyer macrumors 6502a


    Jan 22, 2003
    I hope this is the correct forum

    Here is our setup at church:

    New 21.5" Thunderbolt iMac -> MDP to VGA Adapter -> VGA Distribution Amp -> 3 VGA Projectors at 1280x768

    This problem didn't start until we bought the new iMac. We get constant scrolling vertical lines on our screens. We spent hours trying to find where the interference was coming from. We finally hooked the iMac directly into the projector (we should have done this first) and we still got the lines.

    We tried 2 different MPD to VGA Adapters but that didn't help either. All Apple branded adapters.

    Then we hooked up another 21.5" Thunderbolt iMac and we got the same lines.

    Then we hooked up our Mac Pro with a MDP Video Card and the picture was clear. I hooked up my 2007 MBP -> DVI to VGA and the picture was clear.

    The iMac it replaced was a 2007 that had a mini DVI to VGA and we never had an issue.

    I called Apple and they think that because the Thunderbolt port carries networking, vide and USB that those signals are getting through. He didn't have an answer.

    Is there any adapter or amp we can send the final through that will filter these other signals?

    Sorry for the long post.
  2. Hellhammer Moderator


    Staff Member

    Dec 10, 2008
    You could try mDP to DVI (make sure it's DVI-I) and then DVI to VGA adapter. Sounds like the issue is with Thunderbolt and VGA.
  3. sbruce macrumors newbie

    Dec 1, 2011
    I don't know if you ever figured anything out...but I just replaced a MacPro tower with a new 21.5 iMac @ our church and experienced the EXACT SAME THING! But...I found if I turned off the lights in the room, the scrolling went away. No other computer has the issue, just this new iMac. I stuck an eBtech Hum Eliminator on the outlet and it solved the problem. I think the powersupply in the new iMacs are underpowered or something.

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