Chosen Solution
Hi allmighty gurus from ifixit!!! I have a EMC 2389 21.5 inch iMac it doesn’t turn on the led 4 on logicboard. When startup the iMac have the chime sounds, fans power up, the leds 1, 2, 3 come up and led 4 no come up. I verify all cables from lcd, and are in good conditions. I conected an external display and have image. Can someone help me please. Thanks for your time in advance!
While you did prove the GPU logic is good by connecting to an external lets take a flashlight held on the screen at a sharp angle do you see a faint image of your desktop icons? If you do the backlight logic needs to be checked out. If not, you likely have either a damaged LVDS cable from the display to the logic board or the connector on the logic board was pulled so the connections are not firm. Lets do this take a few pics of the LVDS connector on the logic board looking into the slot as well as from each side at an angle (L&R) and one straight on looking up so we can see the solder joints. Adding images to an existing question
