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I have a mid-2011 Thunderbolt 21.5" iMac. A secondary monitor is connected to the iMac with a Mini DisplayPort-to-HDMI cable (a single cable, not an adaptor and cable).

When I was running Snow Leopard, the monitor worked just fine. After upgrading to Lion, the second monitor just has a black screen, and quickly goes into power save mode.

I have already tried resetting the NVRAM (as described here: http://support.apple.com/kb/HT1379) and resetting the SMC (as described here: http://support.apple.com/kb/HT3964).

Has anyone seen this problem? Any other suggestions for solutions?

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Hmm - several hunches - but can you look in the System Information and see anything about the displays. Is the external seen properly with respect to resolution and connectivity? –  bmike Aug 8 '11 at 17:20
    
Not sure about the info in System Information (currently at work, machine is at home), but the external monitor is not detected in the Display preferences. –  Peter Roe Aug 8 '11 at 17:29
    
It shows physical connections and often helps determine if it's a cabling issue, hardware issue or a driver issue. –  bmike Aug 8 '11 at 17:33
    
Thanks, I'll check this as soon as I get home this afternoon. –  Peter Roe Aug 8 '11 at 17:42
    
Under 'System Information > Displays', the only display listed is the built-in iMac display. –  Peter Roe Aug 9 '11 at 1:22

1 Answer 1

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As it turns out, it was the Mini DisplayPort-to-HDMI cable. I connected the secondary monitor with a Mini DisplayPort-to-HDMI Adapter and everything works fine.

To the best of my knowledge, the cable is fine, although, apparently, it is an unlicensed HDMI cable, and manufacturers can no longer sell them. Has Apple dropped support for these? Not sure. At least everything works again.

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I think OS X 10.7.1 may have fixed that... support.apple.com/kb/HT4764 –  spudwaffle Aug 17 '11 at 15:11
    
I think the HDMI issue listed in the 10.7.1 release notes concerned audio. I actually tried using the Mini DisplayPort-to-HDMI cable both before and after upgrading to 10.7.1, just to be sure that an OS bug wasn't the issue. The secondary monitor only worked after I swapped out the cable for the adapter and cable combo. –  Peter Roe Aug 17 '11 at 17:29

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