Chosen Solution
Recently replaced logic board on iMac and now it wont power up when LVDS is in. When I removed the cable it would power up fine to an external display, RAM, HDD and everything recognized. LED #1 is on when the cable is in but as soon as I press the power button the LED turns off. I have tested the pins with a meter and everything appears fine. I tested again after the power button was pressed, LVDS in, and the pins are still showing power but it will not boot up. I know the screen itself works. Could this be an issue with the power supply? It runs fine as long as the lvds is disconnected, but as soon as I plug in the lvds cable it turns off, no led lights at all. I have also replaced the lvds cable itself too.
At this point I think its safe to say the internal display assembly its self is bad. I’m guessing the T-CON board on the backside of the display assemble under the metal cover has a problem. The easiest way here is to replace the display assembly: Apple P/N 661-5527, LG display P/N LM270WQ1(SD)(A2)
