3 Replies Latest reply: Dec 18, 2012 2:48 PM by transco
transco Level 1 (10 points)

My graphics adapter is an 'ATI RADEON HD5770'.  I have two displays attached, a 23" Cinema HD, and a 20" Cinema.  It has worked OK for a year or so and now I have a problem where the computer 'looses' the 20" display (assgined as monitor 2) at power-up or when waking up from a 'power save, display sleep'.  At first I thought the problem was the display itself, but if I swap displays (swap the ports the displays are plugged into), the 20" works OK and the 23" goes dark (into stand-by).  Doing a 'restart' doesn't help, however, if I unplug the computer and plug it back in again, the problem will go away, and both monitors will start working again.  After a few more daily power-ups, it will fail again, and unpluging and plugging in the computer will 'fix' it for a few more power-ups, then it fails.   To be clear, when I say 'fail', I mean the computer goes back into a single monitor mode.


I discovered this morning that there is one other way to 'fix' it (i.e. getting it back into a dual monitor mode).  Normally I have each monitor connected via a mini display port adapter.  I can get things working again by disconnecting the 20' monitor from the mini display port and plugging it into the 5770's DVI connector.  It will work this way through a few more power-ups, then fail again, this time being 'fixed' by moving it back to the mini display port.  Sorry, I know how confusing all this may sound, but I don't know how to make it any clearer.  My gut feeling is the problem is with the 20" monitor... it fail the power-up handshake and the computer assumes only one monitor is attaced.  Power-cycling the computer or swapping mini display port and DVI port initiates another handshake session, the 20" reports in this time and the computer goes back into a dual monitor mode.  The displays are rather old and no longer under warranty.  I don't want to go to the expense of replacing the 20" until I'm absolutely sure it's the problem.  I could live with it the way it is, but unfortunately it keeps getting worse (i.e. it is failing more frequently).  Any ideas?

Mac Pro (Mid 2010), OS X Mountain Lion (10.8.2), 8 core
  • transco Level 1 (10 points)

    I just saw a thread about how non-Apple Mini Display Port to DVI adapters could cause this problem.  I doubt that it applies, since it's worked perfectly for a year or more using 3rd party adapters (Accell), but I  guess it is posasible.  It sure would be the cheapest solution.

  • Kelly Crossley Level 3 (710 points)

    transco, did you ever resolve this? I'm having the exact same problem. I've already gone through two sets of Accell adapters.



  • transco Level 1 (10 points)

    Sorry, I should have posted this weeks ago...  Yes, I fixed it by installing the Apple 'Mini DisplayPort to DVI Adapter'.  I also was using the Accell adapters.  I can't believe that Accell adapters suddenly went bad after many months of use,  More likely, the Accell's started failing due to some change in the latest update of OSX.  I have two similarly configured Mac Pro's (mid 2010 and early 2008) and both started failing with the Accell adapters and were fixed by installing the Apple adapters.


    I recently had a similar experience with some 3rd party memory modules.  Worked fine for years, then I couldn't even boot the computers.  Replaced the 3rd party memory with the original Apple memory that shipped with the computer and it started working again.  I hate to say it, considering the price difference between Apple hardware and 3rd party equivalents (4 to 1 in the case of the memory), but you're usually better off biting the bullet and buying Apple.