Chosen Solution
Ready to throw it out the window! I can hear it start up but the screen is black. Took it to get fixed and they reset the LCD cable and it worked at the store got it home and back to black. Now what?
I bought an iMac with this problem for a good price to solve the problem. I got it temporary worked around, maybe you can try it. Unplugging the power for a while and putting display brightness to lowest seem to have worked around the problem for a while. I think the built in power adapter or backlight board is the issue. These are both always powered when plugged in. This week this workaround didn’t work anymore and I’ll replace both. I’ll let you know what the culprit was. Dennis van der Pool
I fixed it by replacing the faulty GPU. Same issue; only video at the external video output. I tried another LCD, inverter and powersupply. No succes, so I replaced it with a K1200M with custom firmware. for this issue it’s crucial to know if the external screen is attached as secondary or primary. logon screen at secondary screen: LCD is not being. Initialized due to loose connection. I found out troubleshooting that the external screen is mounted as primary when I disconnect the internal lcd partially. The external screen get primary if the internal lcd is not connected right. if you get a loginscreen at the external screen, this might indicated a loose connection. with the logon screen on the faulty internal LCD you will get a blurred background visible on the external. In my situation this was a result of a faulty GPU that didn’t feed the internal LCD properly.
So I managed to reset my black screen to normal on my 2011 27 inch imac simply by using a labtop in target disk mode to boot up the imac. 1 Put your macbook into target disk mode and connect to imac using firewire or thunderbolt 2 2 boot imac holding down the alt key 3 choose to boot from your laptop drive 4 it should work 5 shut down and disconnect laptop then boot as normal 6 if it doesn’t work either try baking or swapping you graphics card or just give up and throw your imac out of the window in a berserker rage
