Chosen Solution
Hi, My iMac has a display problem. Works perfectly well with an external monitor plugged in so I’ve ruled out the graphics card. It started off just going blank after a couple of hours use. Then it wouldn’t come on at all. Just a quick flash when it was booting and nothing after that. I’ve tried looking at it with a torch to see if it’s just the backlight but not able to see anything. When the LED ribbon cable is connected to the logic board the external monitor works as an extended desktop. When I unplug the cable the external monitor works as the main display. Thinking it’s either the LED that needs replaced or the backlight inverter board but no idea really. Suppose it could even be the logic board itself! Any suggestions on how to narrow the problem down to one thing or the other would be greatly appreciated. Cheers
I would start by running the onboard diagnostics to see if something pops. Sadly diagnostics is somewhat limited here. I would try again to check the display by placing the flashlight directly on the display and then tilting the flashlight at a sharp angle (in a dark place) I would do this where you know you have a few desktop objects as the image will be faint. If you don’t see them at all then your LVDS ribbon cable has a problem or the display its self. Here’s the IFIXIT guide: iMac Intel 27" EMC 2390 Display Replacement . Review Step6 making sure you have the cable in correctly. If you do see the desktop I think you’ll need to do some voltage checking on the LED Driver Board to see if it’s putting out the needed voltages to the display for the backlight. Here’s the IFIXIT guide: iMac Intel 27" EMC 2390 LED Driver Board Replacement. You may need to replace the sync or displays power cable
I have used iStat software to run the fans on “full” on my iMac 27" i7 EMC 2390 which is very noisy but appears to stretch the time in between display failure so it must be due to thermal overload. I did this because the back of the iMac seemed to be too hot for my liking. I can share my screen ok with another computer, so it does not appear to be due to the display logic on the mother board. I may not know what I am talking about because I don’t understand scottclark’s 2nd paragraph. Any discussion on this would be very welcome. Godfrey Bridger
