Has anyones experienced a problem with using a cinema display as a second monitor on a IMac 27, both the IMac and Cinema display will go dark blue and then shut down. These units have been to Apple several times with no fix

I got a cinema display as a second monitor for my IMac 27 and it ran fine until Yosemite. The computer and display were going down on "Graphics display issues". Then Apple replaced the logic board and video card and stated everything checked out. The problem still came back the same day I get it back to my office. I confer with Apple several more times and come to the conclusion that both the display and IMac needs to be in the shop for evaluation. I bring them in once again and they again could not reproduce the issue. I bring the units back to the office and several hours later the screens go dark blue and shut down. Upon re-boot the error message reads that the computer experienced a problem and shut down.

As a side note, the IMac without the second display operates flawlessly.

I am really frustrated at this issue and I really would like to use the second display for my work.

Model Name: iMac

Model Identifier: iMac12,2

Processor Name: Intel Core i5

Processor Speed: 3.1 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 6 MB

Memory: 12 GB

Boot ROM Version: IM121.0047.B1F

SMC Version (system): 1.72f2