imac 27 black screen

  gee-off 12:55 03 Feb 2015

Hi - hope someone can help me diagnose this fault. Imac 27" late 2009

If I shut down holding power button and restart it "sounds' like all is working but black screen. I have to switch on and off a number of times then hey presto normal grey screen and boots up fine - all works great until I shut down or put into sleep mode then here we go again.

Was on Mavericks - now new HDD and reinstall of mountain lion The fault was present before the HD and reinstall of OS I have disabled sleep and HDD shut down etc. So, if the mac goes into sleep mode either automatically or if I click on sleep, it will not wake again with mouse or keyboard, bluetooth or wired.

I have reset SMC/PRAM etc Tried to run with diagnostics mode D or shift D on start up but can't get that to work - also a bit awkward because sometimes the screen starts black ....

I am thinking its not software due to new HDD and reinstall of OS Graphics card?? Display??

Please help


  wee eddie 20:36 03 Feb 2015

I think that you have identified the seat of your problem in the 3rd Paragraph: "now new HDD and reinstall of mountain lion".

I think that it might be worth your while reseating all the connections as one may, inadvertently, have come loose.

  gee-off 13:33 04 Feb 2015

Hi Eddie - problem existe before the replacement drive and IOS changes, so am confident it is not an issue with the HDD. Also I have now further upgraded to Yosemite , still the same issue. thanks anyway

  wee eddie 20:21 04 Feb 2015

What type of Screen does it have?

Could the fault not lie with the back light?

  gee-off 08:20 05 Feb 2015

It's a good point Eddie, may well be - any idea how I can prove either way? Thanks

  wee eddie 13:42 05 Feb 2015

Now, I'm in well beyond my PayGrade, so this is just an idea.

When your screen is black, if there is the slightest hint of what is being displayed, that would suggest that the Backlight has failed or is failing.

  gee-off 20:00 05 Feb 2015

lol, No would appear not -even with a torch...

  StefanSpendel 22:54 16 Feb 2015

i have a similar problem, mac 27 circa 2011, yosemite, screen takes a while to load, then blacks out, not neccesarily overheating as quite cool to the touch, recently done software update, so a possibility there, also recently run dr cleaner program, optimizes memory and cleans junk from hard disk. possibility there as well. leaving it off unpowered overnight to see if i can get into diagnostic mode in the morning as it blacked out before got that far. gut feeling is that its a component failure

  StefanSpendel 08:20 17 Feb 2015

started machine this morning and has been on two hours no problem, couldn't however boot into diagnostics, d, cmd d, option d, dvd in drive, no avail. ran disk util and no issues there

  StefanSpendel 09:03 18 Feb 2015

installed istat to keep an eye on temperatures, no issues there but ram usage almost at 100%, so put a ram optimizer on and removed a few start up apps and computer has run fine for 24 hrs

  JoEdwardes 18:05 01 Aug 2015

I had this problem on my 2008 imac. Screen constantly going black. It became unusable.

The solution? Plug in a different keyboard!

That was it. I had tried every other fix suggested on every forum I could find. PRAM and SMC resets, uninstalling and reinstalling Yosemite, installing smc fan control, you name it, I tried it.

Nothing worked.

Then I plugged in a different keyboard and bingo! All problems disappeared.

imac working brilliantly again :)

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