What are these lines on my iMac screen?

[hallaisen]

Bought this 27" in Feb 2010, and have had these lines show up ever since. They're pretty annoying, but the main issue is that I want to sell it and I can't do that when something is wrong. In the screenshot I just took they are all green, but sometimes they are also red and yellow. They appear most frequently on Youtube or if I use Aperture.

Thanks for any help.


Example 1

Example 2

 

[mulo]

try formatting it, its obviously a software issue as they show up on screenshots, they wouldn't if it was a hardware issue

 

[flatfoot]

try formatting it, its obviously a software issue as they show up on screenshots, they wouldn't if it was a hardware issue

Um, since it shows on the screenshots, it's not a display issue. It could, however, be a graphics card problem –*hardware- or driver-related.

 

[mulo]

Um, since it shows on the screenshots, it's not a display issue. It could, however, be a graphics card problem –*hardware- or driver-related.

graphics card - aka hardware, wouldn't show
driver - aka software, would show

my statement still remains true.
go format it.

 

[leman]

graphics card - aka hardware, wouldn't show

my statement still remains true.

No, you are wrong. If there is a GPU problem (e.g. corruptions in video memory or soem problems with shader units), the artifacts may show up in the screenshots. OS X uses GPU for window rendering (windows are rendered into offscreen buffers first and composited afterwards). A screenshot involves a read-back of GPU memory.

The only case where a GPU error would not show up on the display is when the corruptions happens somewhere between the video memory and video signal output.

 

[flatfoot]

No, you are wrong. If there is a GPU problem (e.g. corruptions in video memory or soem problems with shader units), the artifacts may show up in the screenshots. OS X uses GPU for window rendering (windows are rendered into offscreen buffers first and composited afterwards). A screenshot involves a read-back of GPU memory.

The only case where a GPU error would not show up on the display is when the corruptions happens somewhere between the video memory and video signal output.

Thank you.

 

[hallaisen]

It is definitely not a software issue. I recently replaced my HD, and the lines appear just like they always have.

I talked to Apple support about it earlier today and they refused to repair it for free since my warranty is out. It's my own fault for not doing it within the warranty time, but I was so frustrated at the time. I had driven 3hrs to buy the iMac and 3hrs to get back and the fan was faulty so I had to drive back and get it replaced the following weekend. Then I came back with the new one and it had these lines and I couldn't be bothered going back to replace it. I've bought a macbook, macbook pro, mac mini and this iMac and the mini is the only one that hasn't been defective and in need of minimum 1 replacement. Needless to say I'm not too impressed with their quality control and I'm frustrated that I can't sell this computer now. Anyone know how much I would have to pay to get the graphics card replaced?

 

[tyche]

Are the display glitches all the time or does it have a clear screen and get worse? It could be a heat issue with the card getting too hot.

I've seen this type of display error many times on Windows computers and it was always a bad/dying video card.

As for replacements, these are Apple unique cards but I believe the 27" model is replaceable. This is an example may not be your card model. Price is $180 http://eshop.macsales.com/item/Apple/6615579/