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Thunderbolt Display works with MacBook Pro but not iMac. Huh?

1386 Views 4 Replies Latest reply: May 7, 2012 6:10 PM by Matt Clifton RSS
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May 7, 2012 4:42 PM

I have a Thunderbolt Display, which I normally keep connected as an "extended desktop" to my MacBook Pro -- no problem.


Starting today, I'm using a borrowed iMac and I had hoped to switch my Thunderbolt Display over and do the same arrangement: "extended desktop." However, the display does not come on when I power up the iMac, and clicking the "detect displays" button in the Displays Preferences window does not help.


This iMac was previously set up with an a different Thunderbolt Display in its original home, and seemed to work fine. I saw it with my own eyes. My own Thunderbolt Display still works fine when connected to my MacBookPro. It's only the combination of my monitor to the borrowed iMac that doesn't work.


Both the MacBook Pro and the iMac are running OS X Version 10.7.3. The MacBook has an AMD Radeon HD 6770M card, and the iMac is using an ATI Radeon HD 5750.



Thunderbolt Display
  • Matt Clifton Level 7 Level 7 (26,930 points)

    Are you sure it was the Thunderbolt Display, and not the earlier Cinema Display? The iMac with the 5750 card is the 2010 model, which doesn't have a Thunderbolt port - only the Mini Displayport. It won't connect to a Thunderbolt display.



  • X423424X Level 6 Level 6 (14,190 points)

    Both the mini-displayport plugs and TB plugs are physically compatible which is why you can plug it in.   But if the iMac has a mini-displayport for video it won't work with the TB display.


    Check your System Profile to see if it tells you whether you have a TB port.  And if there is no information about that post here or look up for yourself the kind of ports for that model of iMac.  System Profiler will give yo that information (click Hardware on the left).  From the model information it can be definitively determined whether that imac supports TB.


    Also, so long as the Displays system preferences is not showing an Arrangement tab then it is not detecting the second display.

  • Matt Clifton Level 7 Level 7 (26,930 points)

    The Thunderbolt connector is indeed the same physical shape/size as the older Mini Displayport. Any Thunderbolt-enabled Mac can run both the Thunderbolt display and any of the older Mini-DP displays; unfortunately, only a TB-enabled Mac can run the Thunderbolt display, even though its connector will appear to fit just fine.


    Here's an article comparing the Thunderbolt connection (lightning bolt icon) with the older Displayport (square with two vertical lines either side):





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