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2011 iMac scrambled screen

D

dpilat

macrumors newbie
Original poster
May 6, 2011
7
0
I have a mid 2011 27” iMac. A couple weeks ago, I went to unlock the computer from sleep mode and all of a sudden the screen became scrambled. I was unable to see anything clearly on the screen so I did a hard shut down. Turned the computer back on and, after it bootEd up and the Apple logo disappears, the scrambled screen returned. I am sort of of able to see my login icon and I am able to type in my password. When I click enter to login, the computer will not log in and it stays on the login screen with the scrambled screen. Tried resetting PRAM and no luck.

I booted up in safe mode and was able to successfully login. The scrambled screen appeared to be gone, although the screen was glitchy. Aside from the glitchy screen and the limitations of being in safe mode, the computer seemed to run fine. Powered it down and booted it up normally, and the scrambled screen returned at the login window. I ran the Apple hardware test (by holding down D at startup). The hardware test did not find any issues.

took the computer to the Apple store and they told me it is too old for them to diagnose so that was no help at all

Does anyone know what could be causing this issue? Should I reload the Mac OS software? Any idea what hardware needs replaced given the symptoms? I hate to just scrap this computer as it ran pretty good in safe mode. Apple replaced the hard drive 8 months ago so I doubt it is hard drive related.
 
canyelles said:
GPU problem. Probably difficult to fix because of lack of equivalent GPU
Click to expand...

what do you mean by lack of equivalent GPU? Is the specific GPU mine needs hard to find? Are they expensive? Is the process of swapping out this hardware difficult? Is it not worth replacing?
 
I agree with canyelles' assessment.

GPU failure (the discrete GPU is not used when you boot in safe mode, that's why you were able to boot into safe mode).

Unless you can find a replacement GPU cheap,
and
Unless you can do the physical replacement cheap (as in, "opening it yourself"),
then
Considering its age, probably not worth trying to fix now.

I seem to recall reading that some folks were able to coax the GPU back to life by taking it out, then "baking it" in the oven for a short time to reflow the solder, then re-installing it. But I have no personal experience as to this, and you'll have to do your own research on it.
 
dpilat said:
I have a mid 2011 27” iMac. A couple weeks ago, I went to unlock the computer from sleep mode and all of a sudden the screen became scrambled. I was unable to see anything clearly on the screen so I did a hard shut down. Turned the computer back on and, after it bootEd up and the Apple logo disappears, the scrambled screen returned. I am sort of of able to see my login icon and I am able to type in my password. When I click enter to login, the computer will not log in and it stays on the login screen with the scrambled screen. Tried resetting PRAM and no luck.

I booted up in safe mode and was able to successfully login. The scrambled screen appeared to be gone, although the screen was glitchy. Aside from the glitchy screen and the limitations of being in safe mode, the computer seemed to run fine. Powered it down and booted it up normally, and the scrambled screen returned at the login window. I ran the Apple hardware test (by holding down D at startup). The hardware test did not find any issues.

took the computer to the Apple store and they told me it is too old for them to diagnose so that was no help at all

Does anyone know what could be causing this issue? Should I reload the Mac OS software? Any idea what hardware needs replaced given the symptoms? I hate to just scrap this computer as it ran pretty good in safe mode. Apple replaced the hard drive 8 months ago so I doubt it is hard drive related.
Click to expand...
You should *really* be heading there... ;)
 
Why would it be GPU? That's hardware, which, if failed, would have failed in Safe Mode as well as in a normal boot.

Here's what Safe Mode does per Apple support article https://support.apple.com/HT201262:
Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed.
Click to expand...
In other words, it's highly probable this is a software-related issue.

While in Safe Mode it's very common to have glitchy video, as some video-related extensions may not have been loaded. I suspect the glitchiness in Safe Mode is not related to the primary problem.

Two other ways to narrow the cause:

Boot into Recovery Mode. Since Recovery boots from a separate version of the OS, it helps separate OS-related issues from hardware-related. Since the Apple logo on boot-up is not distorted, I suspect things will be OK in Recovery Mode.

Create and then boot to a new Admin user account. This helps to separate user-specific faults (user-specific configurations and startup items) from faults common to the booted OS. (However, because the issue you're having begins on the login screen, it's less likely to be user-specific.)

Chances are, this is something that's being loaded when the OS loads - the Apple logo is pre-OS, the login screen appears once the OS has loaded. Since it doesn't happen in Safe Mode, that brings us back to startup/login items, system extensions, etc.
 
ApfelKuchen said:
Why would it be GPU? That's hardware, which, if failed, would have failed in Safe Mode as well as in a normal boot.

Here's what Safe Mode does per Apple support article https://support.apple.com/HT201262:
In other words, it's highly probable this is a software-related issue.

While in Safe Mode it's very common to have glitchy video, as some video-related extensions may not have been loaded. I suspect the glitchiness in Safe Mode is not related to the primary problem.

Two other ways to narrow the cause:

Boot into Recovery Mode. Since Recovery boots from a separate version of the OS, it helps separate OS-related issues from hardware-related. Since the Apple logo on boot-up is not distorted, I suspect things will be OK in Recovery Mode.

Create and then boot to a new Admin user account. This helps to separate user-specific faults (user-specific configurations and startup items) from faults common to the booted OS. (However, because the issue you're having begins on the login screen, it's less likely to be user-specific.)

Chances are, this is something that's being loaded when the OS loads - the Apple logo is pre-OS, the login screen appears once the OS has loaded. Since it doesn't happen in Safe Mode, that brings us back to startup/login items, system extensions, etc.
Click to expand...

it’s the gpu

safe mode doesn’t use the discrete gpu
[automerge]1590780010[/automerge]
canyelles said:
GPU problem. Probably difficult to fix because of lack of equivalent GPU
Click to expand...

there are lots of replacement gpu options. some
are cheaper and easier. some less so. pretty much all will allow to upgrade to mojave or catalina if so desired

forums.macrumors.com

2011 iMac Graphics Card Upgrade

iMac 2009 to 2011 MXM3 graphics card upgrade (Lastest update 10/13/2023 - this is the official documentation page - you found it finally!) This is the single and only documentation post. During the last years we constantly updated this post to reflect the lastet development of vBIOS and OCLP...
forums.macrumors.com forums.macrumors.com
 
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