Chosen Solution
Hi all, I have a mid 2011 21.5" iMac and there is no backlight on the LCD. If I shine a torch on the screen I can see all the icons faintly. I can see also see everything on an external monitor clearly. I thought the issue might be with the LED Backlight driver board so I replaced that and no difference, I can still only see the icons faintly with a torch. I then tried another LCD and same result. Icons only visible faintly under a torch. Now I’m starting to wonder, is it a faulty logic board? I read this post here Mac: Signs of a Bad Logic Board (scroll down to Display and Graphics Problems) It’s also not the GPU hence as I mentioned the I can see everything on an external monitor. Does this look like a logic board issue? Everything I’ve done is leading me to this conclusion. P.S. All the diagnostic indicator lights go including the LCD communication one. So the iMac is detecting the screen. Please let me know if you have some advise. Cheers.
The backlight driver board still could be bad its also possible the power feed from the power supply to it is not working correctly either because its cable has an issue or the power supply its self is bad. You’ll need to probe the circuit checking the voltage from the power supply and the LED driver board to see if the power is getting to it and then check the two cables coming from it to the display making sure they too are not damaged and are working correctly. I would test them with the system not powered to start with, checking continuity with an Ohm meter, then testing for voltage.
On the Mac that the backlight isn’t working on I got 10v. On the working one I got 12v. Can someone please check and let me know what the right voltage is ASAP? Cheers
