The Mac starts up and runs probably on thunderbolt to vga adapter but the built in screen remains black. It has an AMD HD 6770m graphics card so not the one under the repair program. Any ideas what could be the problem?

  • …'probably'...? – Tetsujin Jun 19 '15 at 10:40
  • @Tetsujin - maybe OP meant 'properly"? – IconDaemon Jun 19 '15 at 11:41
  • 1
    @IconDaemon Probably. – William T Froggard Jun 19 '15 at 11:43
  • Type in the Terminal command system_profiler SPDisplaysDataType | grep Resolution. You should see the resolutions set for both the built-in and external monitors. You should also try the free app DisplayMenu . You may just have to force a resolution on the built-in display to get it to show. If you can't see the built-in display with either method, it is likely to be a hardware error. Try Apple Hardware Test, too. – IconDaemon Jun 19 '15 at 11:47

Another possibility is your backlight may have gone bad. You can check by holding a flashlight up to the display and looking closely. If you can see the icons on your desktop once illuminated with the flashlight then your backlight is out. This is a relatively simple repair you can have done at the Apple Store.

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