I have a MBP that suddenly stopped detecting an external projector. I have used the same laptop with the same projector before. Right now when I boot the same laptop to the Windows partition it works fine with the projector, so I don't think it is a hardware problem. Any suggestions as to what to try? I have tried the "detect displays" trick and that doesn't seem to work.

  • how many lines do you get back with the terminal command ioreg -l | grep IODisplayEDID Each line should be a connected display. IIRC Windows will ignore an invalid EDID. you can also drop everything after (and including) the | and Command + F for EDID to see the whole tree. might get you doe the right path.
    – hoss
    Aug 12, 2013 at 19:31
  • I only got 1 line when the projector is connected. I've also read about resetting PMU and PRAM but those don't seem to cut it either.
    – JRR
    Aug 12, 2013 at 20:00
  • for whatever reason the Mac is only seeing one EDID device (the LCD). though it works in windows could be a bad adapter. though I'm really not sure.
    – hoss
    Aug 12, 2013 at 20:18
  • Does the screen flash blue when you connect/disconnect the projector? Does pressing command+F1 have any effect?
    – Mr Rabbit
    Aug 12, 2013 at 20:34
  • @Mr Rabbit. No blue flashing at all. command+F1 has no effect.
    – JRR
    Aug 12, 2013 at 22:33

2 Answers 2


I would say it's your adaptor. I had the exact same behaviour. Changed the cables over and it started working again.

I've had it happen on HDMI cable and mini display port/thunderbolt adaptor.


Thanks all. Turns out it is indeed an adapter problem.

For the record, the broken adapter did work for connecting windows partition to the projector, and also for both mac and windows connecting to an external monitor.

And also, even when it works, ioreg -l didn't list the projector's name in the output.

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