Hi, I had a similar issue, the issue is the LCD panel, not the board, I dismantled an old iMac 27 which had GPU gone and I noticed that they share almost the same display. I had to swap the small card on top of the dispaly ( where Video and Function cable is attached (because the one on the imac display have no function cable), reverse the LED cables from left to right and swap the metal frame. It worked perfectly.