Chosen Solution
I have this patern on the display of a 2008 iMac
I am between the LCD or graphics board
That’s definitely the GPU board. Failing GPUs tend to make pretty patterns like that. Please confirm your iMac’s EMC number so we can find you the proper part. How do I find my iMac’s EMC number? Update (11/21/2018) Perfect! Here is a link to a replacement GPU and here is a link to a tutorial on how to replace the GPU.
