HT3924 I can't get my iMac 27" 2009 Mini DisplayPort to work as external monitor for Macbook Air Thunderbolt...

Question

I am using a Mini DisplayPort Cable from iLuv as the connector between them. Upon connecting the cable or hitting Command/F2 on the iMac, the iMac will go blue followed by the Macbook Air, then both will flicker and usually the iMac reverts back to its native screen and NOT display the Air's. Or sometimes the iMac will go black while the Macbook Air becomes very slow and choppy, and while selecting the Gather Windows option in the display window in Settings will show the Imac display window, I can't really do anything with it. I even tried switching the ends of the cable to see if that would help, but it didn't. Advice?

Answer 1

Welcome to the wonderful world of copy protection.
Your display may not be on the "approved" list, or was removed from it.
Apple's Mac lines includes a form of digital copy protection that will prevent protected media, such as DRM-infused iTunes movies, from playing back on devices that aren't compliant with the new priority protection measures.
The Intel-developed technology is called High-bandwidth Digital Content Protection (HDCP) and aims to prevent copying of digital audio and video content as it travels across a variety of display connectors, even if such copying is not in violation of fair use laws.
Among the connectors supported by the technology are the Mini DisplayPort found on Apple's latest Macs, in addition to others such as Digital Visual Interface (DVI), High-Definition Multimedia Interface (HDMI), Gigabit Video Interface (GVIF), and Unified Display Interface (UDI).
Apple has apparently acquired a license for the technology and is now using it across its lines to to prevent transmission of purchased iTunes content (and some DVDs) to devices that don't include support for HDCP.
The problem can often be solved by using an HDMI to Component Video adapter.  Many believe that Component Video will give you a better HD picture than HDMI without any of the hassles of HDCP.
Generally try to avoid using HDMI.   When able, use Component Video.  With Component Video you get full HD quality and you will never have HDCP hassles (which of course is why Hollywood wants to ban it).
However sometimes a display can be HDCP certified and then later be removed from the certified list. So purchasing a new display may not be a permanent solution.