What Could Be Failing? Garbled Screen, Late iMac 2009

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Level 1

130 points

What Could Be Failing? Garbled Screen, Late iMac 2009

Hi. This morning, the iMac's screen went garbled. When I restarted it and repaired the permissions and repaired the disk using Disk Utility, it seems to be ok now. I checked the hardisk on Bootcamp using Speedfan, it's fine, no errors.

What could be failing? Is it software related (OS X 10.9.2 is installed) or hardware relatedIt also says Verified on Disk Utility. That could be failing? Is it software related (OS X 10.9.2 is installed) or hardware related?

The screen looked like these:

Thank you in advance. Have a great holy week & a advanced happy Easter.

God bless, Rev. 21:4, Matt. 16:18, Cor. 13

iMac, OS X Mountain Lion (10.8.5), iMac Late 2009

Posted on Apr 16, 2014 12:16 AM

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Answer 1

andyBall_uk

Level 7

20,516 points

Apr 16, 2014 2:47 AM in response to Alvin777

That looks like a problem with the graphics processor.

Try the Apple Hardware Test on your original install DVD's, although no errors isn't conclusive.

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Answer 2

Alvin777 Author

Level 1

130 points

Apr 16, 2014 3:06 AM in response to andyBall_uk

Hi. It seems to be a Mavericks 10.9.2 bug but It's now good (after repairing permission and repairing disk using the Recovery Mode's Disk Utility).

I tested if it's it's the GPU overheating but it's not. I used the latest Cinebench R15 a few times to load the GPU and the CPU. I've experienced GPU overheating which usually has a garbled screen (3 times already with different computers over the years) and it always becomes garbled right after you turn on the computer.

It's been ok for hours now. I'll observe it tomorrow morning after an overnight shutdown (I'm in the shutdown camp instead of the always on camp) to see if it's a cold solder problem coz' the garbling happened a around an hour or so after it was booted in the morning (a few minutes after it woke up from sleep- 10.9.2's sleep might have a bug).

[ It's a blessing in disguise it happend coz' it forced me to download iStat's latest monitoring app which has interesting sensors (like how many watts the Mac uses when the screen is full bright vs. 11 tick on the screen brightness. It's a difference of around 40 watts only when it's not on heavy load like rendering. GPU significantly takes less power when fully loaded which makes GPUs great as CPUs if they replace the usual CPUs). iStat menu is tempting to buy. ]

God bless

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Answer 3

andyBall_uk

Level 7

20,516 points

Apr 16, 2014 3:45 AM in response to Alvin777

I'm glad that it's now working normally.

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Answer 4

Alvin777 Author

Level 1

130 points

Apr 17, 2014 10:14 PM in response to andyBall_uk

Hi. Thanks. It's a bug in the 10.9.2's anti-aliasing in it's OpenGL driver. I switched off anything is anti-aliasing related like font and line smoothing ( in OS X, System Preference - General - LCD font smoothing), Preview it's line smoothing in its preferences, games it's anti-aliasing, on other apps like painting or photo editors, it'lll be switch off too.

How I tested:

https://discussions.apple.com/thread/6099847

God bless.

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