I have 21.5 inch Mid 2011 iMac, it was able to working as external display use the thunderbolt cable, but few month ago, it stop working. I press COMMAND+F2, nothing happens, it was able to have a black screen and became an external display from my Mac Pro Book.
How I can know if there is a software or hardware issue?
iMac (21.5-inch Mid 2011), OS X El Capitan (10.11)
in Launchpad->Other->System Information->Hardware->Thunderbolt can have diagnostic information of the connection of Thunderbolt cable. Unplug and plug, it turns out I mis-connected (up-side-down) the Thunderbolt cable on my Mac Pro!
I was not aware of it's so easy to mis-connect the Thunderbolt cable, especial in Mac Pro Book.
It's working now. I am glad able to resolve this issue by just asking, and by myself!
in Launchpad->Other->System Information->Hardware->Thunderbolt can have diagnostic information of the connection of Thunderbolt cable. Unplug and plug, it turns out I mis-connected (up-side-down) the Thunderbolt cable on my Mac Pro!
I was not aware of it's so easy to mis-connect the Thunderbolt cable, especial in Mac Pro Book.
It's working now. I am glad able to resolve this issue by just asking, and by myself!
And, it's also helpful to use the Console application, which can find through LaunchPad->Other->Console
When it launch, as soon as you plugged in the cable, it will dump out IO Thunderbolt related information. This helped me figure out the former not working was a Thunderbolt Cable issue, the old cable has a pin missing. And this also answers my question of - not working few month ago. With the new cable and new debugging way, I have more confidence to use the external display.
21.5 inch Mid 2011 as external display failed, but it was working!
