Yosemite broke Target Display Mode on my iMac

[megalaser]

Hi, I have a 2011 27 inch iMac that I have been using as a monitor for my Mac Pro via a Thunderbolt cable - the iMac was in Target Display Mode (TDM), I just upgraded the iMac from Mavericks to Yosemite and now it does not go into TDM, if I hit Cmd/F2 as previously the display just breaks up and freezes - does anyone else happen to have this problem please? Thanks!

 

[rainydaze]

Me too...although when I press cmd-F2, nothing happens to the external display, it just keeps ticking along as normal. I've tried both boot orders, unplugging and replugging.

When I first installed Yosemite, it worked fine, but then when I installed the minor version update, it stopped working :-( Perhaps I can go back to 10.0 somehow...