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Main monitor flashes blue over and over with 2nd monitor connected

884 Views 18 Replies Latest reply: Aug 15, 2013 11:28 PM by mrbofus RSS
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William Donelson Level 4 Level 4 (2,495 points)
Currently Being Moderated
Jul 8, 2013 11:27 AM

My old 23" cinema display died, and I have a new 24" DGM 1920 x 1200 display with DVI input.



I have a Thunderbolt to DVI male cable which connects from the iMac to the DGM display. It was working fine earlier, but when I woke up from sleep, the login screen flashed blue then login then blue, over and over about once every 3 seconds.



Now if the second monitor is plugged in the main iMac screen flashes blue every 3-4 seconds, over and over.



Any ideas?

iMac (27-inch, Late 2012), OS X Mountain Lion (10.8.3), 1TB Fusion drive, iPhone 5, dual G5
  • BDAqua Level 10 Level 10 (114,745 points)

    Hi William,


    See if it's related to this...


    The 2012 macs (and later apparently) not waking normally from sleep after hours being in sleep. (noted here ...



    "Why 2012 iMac/2012 Mac Mini won't Wake After Hours of Sleep (Hibernates/Powers Off)")


    The sleepimage file still reappears even if never slept. Delete it (hibernate off, etc) - within minutes its back.


    A note on that here -


    About iMac sleep...


  • BDAqua Level 10 Level 10 (114,745 points)

    Ah, then it's just not after sleep, not the aforementioned problem then.


    Does it do it if you boot into Safe Mode with shift key held down?

  • BDAqua Level 10 Level 10 (114,745 points)

    Is this with the second Monitor still hooked up?


    If so disconnect it &...


    Open console in Applications>Utilities, check the system log for the date/time of the last problem  & the Startup right after that for clues.

  • BDAqua Level 10 Level 10 (114,745 points)

    I was thinking something about that second monitor or cable is trouncing the System, you can see every second or 2 that the internal is going on/off...


    08-07-2013 20:54:59.778 WindowServer[103]: Display added

    08-07-2013 20:54:59.778 WindowServer[103]: Display removed


    So some signal line or possiby a ground loop I'd say.

  • BDAqua Level 10 Level 10 (114,745 points)

    Given that, then either OSX isn't communicating well with the Monitor on wake, or vice versa, but apparently 2012 Macs have known sleep/wake problems.


    I myself would be tempted to try the sleep fix here...


  • BDAqua Level 10 Level 10 (114,745 points)

    Well, I'm not aware of anything there doing it, but so little is known about those by me.


    Are there any USB things attached to the second Monitor?

  • mrbofus Level 1 Level 1 (5 points)

    Did you start experiencing these issues after the 2013-003 security update? 


    I started a similar thread, except in mine, the iMac display itself is randomly turning off.  Thread is here:

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