William Donelson
Level 4 (2,520 points)
Mac OS X

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

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

Posted on Jul 8, 2013 11:27 AM

by William Donelson,Solvedanswer
William Donelson William Donelson
Level 4 (2,520 points)
Mac OS X
A:

It seems that Apple change the mini-Display parameters, perhaps to kill off 3rd party connectors, not sure.

 

I tried 4 different mini-Display to DVI adaptors. All of them used to work fine, but only one works now.

 

Same thing happened with previous monitor; the md-to-DVI worked fine for a while, then on a system update it stopped working.

 

I think if you have random blue screen on your main system, it might be a loose cable, so OSX detects a loss of monitor and resizes desktop, then the connection gets solid again and again Blue to resize etc

 

Just speculating

Posted on Jul 9, 2013 2:11 PM

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William Donelson

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

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  • by ileob,

    ileob ileob Jul 10, 2013 12:51 AM in response to William Donelson
    Level 1 (0 points)
    Jul 10, 2013 12:51 AM in response to William Donelson

    Hi William,

    I am encountering a perhaps related problem with my Thunderbolt monitor on a 13" mid-2011 MacBook Air. Since having installed the security update 2013-003, both keyboard and ethernet which are both connected to the screen, sometimes won't work. The screen is always there, however. This only happens when I arrive at the office with my laptop and connect the screen. I also haven't yet found a consistent solution (it has happened only twice so far, but never before the update), but my current "method" is to restart the Mac without the monitor attached and then connect later. Of course that won't help in your case...

    I will also file a bug report with Apple, hoping that it gets their attention.

    Best,

    Leonard

  • by William Donelson,

    William Donelson William Donelson Jul 10, 2013 1:15 AM in response to ileob
    Level 4 (2,520 points)
    Mac OS X
    Jul 10, 2013 1:15 AM in response to ileob

    I also noticed a new effect last night...

     

    When I put the iMac to sleep, both monitors go dark and power drops down low (I have a meter).

     

    But if I unplug my iPhone or a USB device, the iMac wakes up "a bit" although its screen remains "black", but the 2nd monitor comes on "with signal" although it too is "black display". It never falls back asleep; never loses signal. Power usage is up a bit.

  • by William Donelson,

    William Donelson William Donelson Aug 15, 2013 1:29 AM in response to William Donelson
    Level 4 (2,520 points)
    Mac OS X
    Aug 15, 2013 1:29 AM in response to William Donelson

    There appear to be at least 20 threads regarding Thunderbolt/DisplayPort problems, so I assume Apple still have not worked out good drivers for the variety of monitors and display resolutions out there.

     

    Generally, turning the external monitor off for 15 seconds seems to work for me, but it's a real hassle...

     

    Very frustrating.

  • by mrbofus,

    mrbofus mrbofus Aug 15, 2013 11:28 PM in response to William Donelson
    Level 1 (23 points)
    Mac OS X
    Aug 15, 2013 11:28 PM in response to William Donelson

    In my case, it's not an issue of the iMac's screen flashing blue, the iMac's screen just simply randomly turns off.  I posted an update in the thread I started [ https://discussions.apple.com/message/22404953 ] where the issue seems to go away if I don't let my computer go to sleep.  If I don't let the iMac go to sleep, then the screen turns off and on as it should. 

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