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External Display Problem - SMC Reset Required After EVERY Restart

I have a mid-2010 macbook pro that I often use in Clamshell mode with an external display (an ASUS VS239H-P 23-Inch Full-HD LED IPS monitor). I connect to my monitor with an Amazon brand HDMi cable via a Monoprice Mini Display Port to HDMI adapter. I'm running OS X 10.8.4.


Here's the problem... whenever I go "mobile" and disconnect my macbook pro from the external display, my macbook seems to work fine at first, but if I ever need to restart my macbook, it thinks it is still in clamshell mode upon reboot. The built in display stays dark, and if I close the lid, the power indicator lights up and stays lit up; if I open the lid, the light disappears. It doesn't even matter if the power cord is plugged in or not, the computer thinks it is in clamshell mode. This occurs ANY time I restart my computer, whether I'm booting into bootcamp or OS X. If I do an SMC reset, I can successfully restart my computer. But if I ever need restart my computer again, and I haven't reconnected to my external display, the problem happens all over again. The only other way to fix the problem is if I plug my external display back in, then unplug it, which seems to remind my macbook that the display has been disconected. Unfortunatley I can't do this if I'm out for business and my display is not near me.


What gives? What can I tweak to fix this? I'd rather not have to wipe the HD and do a fresh install of the OS.

MacBook Pro, OS X Mountain Lion (10.8.4)

Posted on Jun 23, 2013 2:22 PM

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External Display Problem - SMC Reset Required After EVERY Restart

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