Chosen Solution
Hi guys. I have a 2009 27” iMac with the HD 4850 card which has died or is failing (horizontal lines across the screen). From researching here I see that card can be replaced with a more powerful HD 5750. I am wondering can I reuse the heat sink assembly from the 4850 and just purchase the 5750 chip on its own ? Thanks in advance for any advice.
Are you sure the issue is the GPU and not the display its self? I would connect an external display to your system via the miniDP connection. If the external display is good then your display is the real issue not the GPU board. I prefer this method to be sure. Another way is to boot up under Save mode Shift (⇧). Unlike your normal boot this will use the Intel GPU engine within the CPU. Is the image clean?
