iMac multicolored vertical lines on screen & won't boot

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Level 1

34 points

iMac multicolored vertical lines on screen & won't boot

Hi

I have an Early 2008 (yes, I know, time to upgrade) iMac 20" (2.66 GHz) running El Capitan (10.11.6), on which it looks like the graphics card has failed - my 2008 iMac 24" did roughly the same thing a year ago.

The problem started during normal operation - the screen was suddenly covered in sparkling, multicoloured vertical lines and the cursor changed to a large, inch square, box. Although I could move the box-like cursor, nothing on the screen was clickable.

On reboot it got about two thirds through the start-up progress bar and then went to a blank grey screen with no lines. And there it sat.

Based on some advice I received last time, I tried to isolate the issue by forcing the OS to boot off the onboard Intel graphics card...to check that it was indeed a problem with the external ATI Radeon card. This I did by booting off an external drive with a slightly modified OS - the ATI and AMD extensions removed.

The iMac then booted all the way to the desktop...however, there are still vertical lines. The cursor is back and functioning and aside from the very slow graphics rendering of the Intel card, all is working fine.

So, I can't boot on the Radeon card, but it boots and works fine on the Intel card...but the screen is still full of vertical lines - mainly red now...and still sparkling a bit.

Any thoughts on what other video / screen component could be at fault?

Your replies greatly appreciated.

Regards

Posted on Nov 26, 2018 11:30 AM

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Answer 1

Kappy

Level 10

361,741 points

Nov 26, 2018 11:39 AM in response to Mr Badger

If you don't know how to repair the computer then you will need to buy a new computer. Your model is now obsolete and unsupported. An Apple Store will not repair it for you. How to find your nearest Apple Authorized Service Provider (AASP) or Distributor (AAD). They may also be unable to help because they cannot buy any parts from Apple. So you are left with two options: fix it yourself or buy a newer computer.

If you decide on the first option then check out iFixIt and OWC for parts and/or tear down tutorials. Also, search the Internet for additional help.

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Answer 2

Kappy

Level 10

361,741 points

Nov 26, 2018 12:05 PM in response to Mr Badger

I'd guess the GPU given what you've already reported. It is also possible the display is failing. You should try using the Apple Hardware Test to see what it reports.

Intel-based Macs- Starting up into Apple Hardware Test

Apple Hardware Test- iMac (Mid 2007) and later models

upekkha-AppleHardwareTest · GitHub

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Answer 3

Mr Badger Author

Level 1

34 points

Nov 26, 2018 11:57 AM in response to Kappy

Thanks Kappy. I was aware of all that and I am attempting to fix it myself, I'm just trying to narrow down the component I need to replace. I have five of these Early 2008 iMacs and have performed full strip-downs and multiple component replacements before, so more than capable of performing the fix if I can isolate the component at fault. As for parts, they are available, although used, and you have to ride your luck a little.

Just looking for component failure clues from the good folk on here.

Regards

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Answer 4

rkaufmann87

Level 10

140,682 points

Nov 26, 2018 12:11 PM in response to Mr Badger

Mr Badger wrote:

Hi

It's unlikely that both the Radeon and Intel GPUs have failed at exactly the same time...unless there's another video component I'm missing here.

Regards

The Radeon IS the GPU!

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Answer 5

Mr Badger Author

Level 1

34 points

Nov 26, 2018 1:01 PM in response to rkaufmann87

I know. I’ve disabled the Radeon GPU and it’s now running on the integrated Intel GPU. Its still got vertical lines but it’s booting fine, the cursor is working and aside from the slow graphics performance of the Intel GPU, all is well. I’m now trying to narrow down what component would cause lines when it runs either of the two internal GPUs.

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Answer 6

rkaufmann87

Level 10

140,682 points

Nov 26, 2018 11:53 AM in response to Mr Badger

The GPU has likely failed, considering the age of the computer and the availability of parts it is not worth fixing. It's time to replace the computer.

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Answer 7

Mr Badger Author

Level 1

34 points

Nov 26, 2018 12:03 PM in response to rkaufmann87

Hi

It's unlikely that both the Radeon and Intel GPUs have failed at exactly the same time...unless there's another video component I'm missing here.

Regards

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iMac multicolored vertical lines on screen & won't boot

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