Since upgrading to Yosemite my thunderbolt display keeps randomly going black. I have to switch it on and off numerous times before it eventually springs into life. I have IMac 27". 3.4GHz 8GB Ram. AMD radeon HD6970M with external thunderbolt display. It will not run the firmware update - just says it failed and the device has been removed
iMac, OS X Mavericks (10.9.2)
Tur off the Automatic Ajust Brightness
I am having the same problem. I have an iMac 27 with two thunderbolt displays. Many times when the displays "go to sleep" the two thunderbolt displays don't come back up. I have to either cycle power to them or disconnect and reconnect their thunderbolt interfaces.
This is happening to me as well, though its through a dock and hdmi.
It seems that its an issue with the ports, and USB ones as well, as i've been finding it online.
Thunderbolt display keeps going black
