Screen won't come on when iMac powers up

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Level 1

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Screen won't come on when iMac powers up

This started as an intermittent problem a couple of weeks ago that could be fixed by switching power off at the mains and then re-starting the computer. Then yesterday when that didn't work I re-set the PRAM and that did the trick. Today, nothing will remedy the problem. The computer powers up, chimes happily, then the white lamp at bottom right glows steadily while the hard disk does the usual churning away. The lamp stays on and the screen does nothing.

The affected machine is an Intel iMac, Core Duo, with Snow Leopard. It used to be our main machine but for the last two months has been sitting on top of a Clavinova running little more than Garageband and a simple USB MIDI interface.

The unit had a replacement motherboard about three years ago when it suddenly died and it had a replacement screen about a year ago when it developed the well-known vertical lines issue.

I can access the computer via Screen Sharing from our new iMac. It seems to be working normally although to be honest when I look in the System Profiler I'm not altogether certain what I'm looking for as regards diagnostics.

Does anyone have any ideas what I can try to get this fixed, short of taking it in for repair (which, unless it's a trivial repair, I can't afford to do as I can't justify the cost to keep two iMacs running in the house)?

Intel iMac, Mac OS X (10.6.8), Core Duo

Posted on Dec 6, 2011 9:54 AM

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Answer 1

towny Author

Level 1

5 points

Dec 6, 2011 10:58 AM in response to towny

By the way, the graphics info in System Profiler looks like this:

Anyone know which bit of the system is broken, according to this? If there's no clever keystroke combination to fix it, will an external monitor used in mirroring mode do the job? I'm quite happy to have a cheap, cheap 2nd hand LCD panel off eBay and stuff the iMac under the piano.

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Answer 2

R C-R

Level 6

17,782 points

Dec 6, 2011 12:03 PM in response to towny

If you can find the original system disc for this iMac, try running the Apple Hardware Test for it. (See the "Additional Information" section for more about that.

This may give you an error code that will hint at the source of the problem.

Since you can see the display via Screen Sharing, you probably can use mirroring & external display, but that is only a (kinda) educated guess.

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Answer 3

towny Author

Level 1

5 points

Dec 6, 2011 12:19 PM in response to R C-R

Thanks, I will dig out the discs and try that. Does it need to be the original? I have the Snow Leopard Family Pack which I used to upgrade from 10.4 to 10.6 - would that work if I find it first?

Also, something odd ... I went back to the computer just now, having left it disconneced from the mains for half an hour or so. It started up perfectly normally, screen and all. I re-started it, it worked again. Then I sent it to sleep from the login screen. When I clicked the mouse to awaken it, it re-started as if from cold but came on without the screen working. So I'm back at square one.

Does this very odd behaviour help anyone suggest the problem?

Meantime I'm off looking for the discs.

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Answer 4

towny Author

Level 1

5 points

Dec 6, 2011 1:12 PM in response to towny

Reporting back:

AHT says 'No trouble found'. The offending iMac is now behaving itself as I power up, log in and then power down from the Apple menu. I've not tried sending it to sleep again; that's what reproduced the problem earlier this evening. At the moment I'm inclined to quite while I'm ahead and simply not allow the iMac to sleep.

Has anyone ever heard of sleep operating incorrectly and causing the symptoms I have described above?

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