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I just upgraded to Yosemite on my 2009 MacBook Pro and now it won't detect the external display. It worked perfectly before the upgrade. I have the display connected by USB. Is there anything that can be done about this? I really need that external display for work and am really regretting downloading Yosemite.
MacBook Pro, iOS 8.1
Exactly the same issue. My Eizo Coloredge was working fine after installation until (just now) I dared to do a restart...
I have tried various different displays and connections over the past 20 minutes and have restarted my mac (late 2013 MBP 15' Retina) and connected / disconnected multiple times. Neither my Coloredge via Thunderbolt or HDMI (no signal detected) is recognised, nor a Samsung LCD via HDMI.
SO frustrating that something this basic should now be 'broken' when it was fine under Mavericks (and earlier OS). Come on Apple, let's get a fix. Plenty of people rely on external monitors.
Sigh.
.
After several hours searching for a solution, this worked with my macbook pro 2012 with sony TV external monitor.
1. Connect external monitor to macbook. Since external monitor cannot detect any source, let it go to standby power mode by itself.
2. Go to "system preferences" then "displays".
3. Press alt and click "detect display" button.
External display will then wakeup from power standby mode.
Cheers
Upgraded to Yosemite and now external display is not detected
