Chosen Solution
Based on a lot of research, my iMac was suffering from the vertical lines hardware display issue and I found a place on eBay that replaced broken GPUs. After replacing my video card the screen is still black. I see the backlight come on during boot and I can control the computer, play music via keyboard shortcuts etc, but no images display, no boot apple logo, etc. I’ve checked the cables like 10 times and rebooted this thing so many times. What else can I try? I’m about to give up on this beautiful machine that still works but seemingly something is out of place. I replaced the vsync cable after a damaged one and that was working okay. What else can I try to revive this iMac and resolve this pesky display issue?
Are you able to see a proper image on an external display? I would start there. If the image is good on the external then you know the issue is localized within the internal displays connection or the internal display its self. More often than not I find the logic board connector gets yanked to the point it fails to make proper connection to the ribbon cable and/or the ribbon cable is damaged. You’ll need to take some pics of the connector so we can see if it can be recovered or if you needed a new connector. The other possibility is the cable was installed backwards which can damaged some parts on the logic board, just below the LVDS connector see if any of the components are burnt.
Dave Rau you replaced the video card or you got it repaired. The way you describe the error it sounds like a video card error. You may need to consider replacing it once more.
