Chosen Solution
Hello excellent iFixit community, I recently diagnosed a client’s iMac as having a failed LCD panel. I mentioned to him he could use it only with an external display, and he accepted this solution, at which point I disconnected the LVDS cable, backlight power cable, and V-SYNC cable. I left the LCD temperature sensor cable connected. This setup worked for me in the shop with an external, but apparently didn’t work for him when he took it home and tried it several weeks later. He brought it back into our shop, and I confirmed my external display no longer showed an image - either during boot or at the user login screen, even after resetting PRAM and the SMC. I opened it up, connected the VSYNC cable for the heck of it, and the external worked - it displayed the boot screen. Strange. I disconnected the VSYNC, and tried again. The external monitor still worked - even though this was exactly the same configuration that didn’t work 5 minutes before. Was I wrong to suggest that disconnecting his internal display would provide a reliable solution? If not, does anyone understand what’s going on?
Why don’t you leave the connections active? I suspect the lack of power while in transit is the cause here. Update (10/17/2016) While you can run the system with the internal display disconnected for diagnostics. I’ve never tried running a system like what you are doing here. Is finding a workable LCD screen that costly?
Maybe we’re talking about something different , I’m typing this text on an imac with a dead lcd screen and plugged into my 28 inch Asus monitor…I don’t reset it everytime, works just fine this way until I replace the Lcd display… I use a mini display port to HDMI… It’s a quick fix for anyone who loses their display at a bad time.
Use command +F1 to boot to external display on start up…. Four out of five voices agree.
I have a similar issue. The backlight has failed on my mid-2010 iMac 27”. I now have an ultra HD 35” widescreen monitor connected vie display port and that works fine. The only problem is that sometimes I will open an app but it will appear on the iMac screen instead of the external one. This means I cannot see the app! What I need is a way to make the external screen the ONLY one and not as part of an extended desktop to the internal iMac screen. I have yet to find a way to do this so if anyone knows a way please let me know?
I have the same issue going on with my 2013 iMac, whose display has passed on. I was using an old Apple display as a 2nd screen but not set up as the log-in screen. I did a bunch of things suggested here and elsewhere, and even saw that there is a shortcut for forcing the displays to mirror : Cmd+F1 (or Fn+Cmd+F1 (though I haven’t tried this). Instead, I tried connecting to the dead-display iMac via screen sharing. Voila! The login screen came up on that computer. I was able to log in, went to preferences/displays/mirror displays. Now I am able to work on this computer again, albeit with a single display.
same situation here: my iMac 21” 2007 started to shows bad lines on video, getting worsen untill all screen was unreadable; I configured an external monitor as mirror, permanently attached via mini Display Port > HDMI. Works well, even now that the boot from internal HD is failing one time over three. So I decided to clone OSX 10.11 (El Capitan) onto a 128GB microSD card, plugged via USB reader, making it primary boot disk, and guess? Works even faster!!! I suggest to try this , when you have no other options, to continue using this cool Mac.
