2 Replies Latest reply: May 8, 2013 2:01 PM by DakotaDude
Chrash78 Level 1 (0 points)

I have a 21.5-inch, Late 2009 iMac running Mountain Lion 10.8.3.

I've had my iMac connected to my 42" LG HDTV for several years using a Mini Displayport to HDMi adaptor > HDMi to HDMi cable - using it as both a mirrored & Extended display.

I recently unplugged my iMac (and all my other peripherals) from my TV (for some 'spring cleaning' & only for around an hour) but now my iMac can no longer detect my TV.

Now when I switch it on my LG TV says 'No Signal' (for the first few hours of trying when I turned on my TV (on the correct AV channel of course!) I would get a flash of blue screen on my iMac, then nothing would happen and I would just get the 'No Signal' message on my TV).

I have searched for solutions on numerous forums - unplugging, plugging-in in various arrangements. The 'Detect Displays' option doesn't do a thing.

I've tested other peripherals in the HDMi ports on my TV and they all work. I've tried PRAM resets, system restore settings, rolling back time machine etc etc...

I'm loathed to buying another cable as I know this one works, and it must just be a software issue as the iMac (was) detecting the TV.

I don't have another HDTV with HDMi to test it out - but I know it is a problem with the Mac and not the TV...Has anyone come accross this/a similar issue? Is there a solution?

iMac, OS X Mountain Lion (10.8.3), iMac not detecting external display
  • NerdMachine Level 1 (5 points)

    I have the exact same problem although on my Macbook Pro from 2012 using a Mini Displayport to DVI adapter.  I can sometimes get it to work by putting the computer to sleep, unplugging&replugging the displayport, and then waking it up.  For me, it started happening in 10.8.2 and then seemed to get worse in 10.8.3.  I suspect it might be hardware that's slightly out of spec and thus detects the displayport change but then don't go any further.

  • DakotaDude Level 1 (0 points)

    I have identical problem and did not experience until 10.8.3 when the Display icon was removed from the toolbar.