Q: when i wake my iMac up my LCD cinema display doesn't wake up unless i unplug it.

Hi all

When i wake my iMac up my 2560 x 1440 LCD external cinema display doesn't wake up unless i unplug it from the thunderbolt port in the back of my iMac.  I've a 27 inch mid 2011 iMac on 10.9.5.  the external cinema display is apparently using DisplayPort.  any ideas?  thanks, R

LED Cinema Display:

  Display Type: LCD

  Resolution: 2560 x 1440

  Pixel Depth: 32-Bit Color (ARGB8888)

  Display Serial Number: 2A1104XN6JL

  Mirror: Off

  Online: Yes

  Rotation: Supported

  Connection Type: DisplayPort