iMac display shows yellow vertical bars and wont boot

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iMac display shows yellow vertical bars and wont boot

Just yesterday I came into to look at my iMac and the display was frozen with lots of yellow "dots" all over the screen and totally unresponsive. I. managed to ssh in to it, so it was working, and then performed "sudo reboot". When it rebooted, the screen was grey with large yellow bars down it and it would not boot completely.

(Sorry it's the wrong way up, but you get the gist...)

I've reset the PRAM and booted into safe mode. This takes a very long time, but I do manage to get a login screen and the desktop, but with VERY slow video performace, and still have 5 yellow/blue stripes down the screen. After logging in, I can reboot it back into normal mode, but it sticks at the apple logo screen and fails to continue.

I've attached photos of the boot screen and the safe boot desktop.

Since this is late 2009 Mac, its well out of warranty, but any ideas would be welcome.

It's sort of usable in the current form, but not really for video and Safari web pages look really bad

iMac, macOS High Sierra (10.13.2), 16G RAM, Intel Graphics Adapter

Posted on Dec 22, 2017 2:50 AM

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Answer 1

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apjimmy Author

Level 1

11 points

Feb 19, 2018 3:13 AM in response to John Galt

Final update on this issue. I decided I needed a new iMac anyway and decided to fork out for one, but didn't give up hope on my old machine. I got the disk taken out by the repair shop so that I could migrate to the new machine and did so.

In the intervening time, I looked online and iFixit and other places had information on potentially fixing GPU issues with, what a colleague here called the "Hail Mary" (last resort option) of baking the GPU in an oven for 9 minutes.

So, I looked at the options, and decided to give it a go. There are two videos by the same person on this; the second being when his original "bake" failed after a few months. I decided to follow the 2nd of the two as it didn't require the removal of the motherboard, but only the GPU - it looked much simpler. My hardware experience has been limited in the past to adding new cards in PC's and replacing BIOS batteries.

After purchasing the required tools (suckers for the screen and some torque screwdrivers and thermal paste) I went ahead with his instructions. It's not an easy process; but most/all of the fiddly work was in fact re-assembling the LCD panel.

GPU removed, and heat sink detached, I baked for 9 minutes at 200 Celsius, waited for it to cool and proceeded to re-assemble everything.

It worked! I now have a working 2009 iMac alongside me new 2017 iMac.

So, if anyone does see these same symptoms and is willing to give it a final go, I'd recommend trying the baking method as it worked for me. And if all else failed, you had nothing to lose anyway.

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Answer 2

John Galt

Level 10

155,810 points

Feb 19, 2018 4:29 AM in response to apjimmy

"Baking" to re-flow the GPU solder connections definitely works, but it's temporary. However, that "temporary" may turn out to be many months.

I don't advocate that solution on this site because most people don't know which end of a screwdriver to hold. If I did though, I'd set the oven for 350° F for 25 minutes, and leave it in as it cools. Also, suspend it from wires—don't let it rest on a surface.

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Answer 3

sterling r

Community Specialist

Dec 22, 2017 3:30 PM in response to apjimmy

Hi apjimmy,

I understand you're seeing vertical yellow bars across you screen and this has not been resolved by booting to safe mode or by a PRAM reset. I know it's important for your Mac to function properly and I'd like to help. Based on the steps you've taken and the screenshots provided I'd recommend having the Mac evaluated and an Apple Authorized Service Provider to see what options may be available. You can find the nearest location to you here: Find Locations

Best Regards.

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Answer 4

John Galt

Level 10

155,810 points

Jan 5, 2018 6:40 AM in response to apjimmy

There are other options. PowerBook Medic is a reputable company that I have used in the past. Despite the name they service iMacs also. They've been around a long time.

it may take a long time (months, possibly)
it will be expensive

... but you might be surprised.

Economically speaking it makes more sense to buy a new iMac. Or, just use yours in its present state until it becomes unbearable.

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Answer 5

apjimmy Author

Level 1

11 points

Jan 5, 2018 3:48 AM in response to sterling r

It's a hosed video card. Unfortunately, due to the age of the machine, it doesn't look I have many options. Which is a real pain as I just had the disk upgraded to a 1TB SSD just 3 months ago.

Does anyone know of any other options open apart from forking out for a new iMac?

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Answer 6

apjimmy Author

Level 1

11 points

Feb 19, 2018 7:32 AM in response to John Galt

I rested the GPU card on 4 foil pyramid, each resting on the screw holes of the GPU. I also did leave it to cool in the oven, as I was wary of the sudden heat->cool and the effect it may have on the components.

As I said, it really was a last resort as I had already forked up the money to buy a new iMac, so having this for a bit longer was now more of an "bonus" for me. To be honest, I'll probably now just use it as a 2nd monitor for my new iMac in target display mode, but all of the 4 core i7 goodness just seems a little wasted on that....

It's certainly not for the faint-hearted, as putting back some of these connectors was very fiddly and resulted in quite a bit of swearing and almost giving up, to say nothing of trying to get the monitor screwed back on whilst the magnets try their best to stop you.

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Answer 7

John Galt

Level 10

155,810 points

Feb 19, 2018 10:23 AM in response to apjimmy

It gets better with practice. Especially when you reassemble everything without a single speck of dust behind the glass only to realize you forgot to plug in a thermal sensor. Not that I would know anything about that.

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