What is wrong with my iMac? (video corruption, unstable)

I have a 24" Early 2009 iMac.

During "intensive" use (such as Photoshop, WebGL, etc.), the system starts to become very unstable, resulting in bizarre graphics corruption and other weird behaviour. Ultimately, the machine freezes or crashes.

Somehow I managed to take a screenshot just before it went down, and I was surprised that it captured the carnage. I've censored (blurred out) some names to protect the innocent, but all the other glitches are part of the corruption.

I ran a temperature monitor in the background during use, and although it increased (as expected), it didn't seem to show unusually high readings for any components.

Anyone have any idea what could be wrong? Should I try reinstalling OS X from scratch, or is this definitely a hardware issue?

Setup:

• 2.93 Ghz Intel Core 2 Duo
• 4GB RAM
• GeForce GT 120 256 MB
• OS X 10.8 (upgraded from Leopard, then Snow Leopard)

EDIT:

Having said that the components' temperatures seemed well behaved, I have started to notice that the problem occurs more readily when my room is warmer. Wondering if it is a heat-related problem...

EDIT 2:

Reinstalled OS X from scratch, but problem persists. I think this indicates a hardware problem. Sadface. Will open it carefully, hoping I'll find a busted fan or something silly like that. Otherwise, will take it to the shop - not keen to mess about with hardware even though it's out of warranty as the machine is still worth a fair bit I'd say.

Solution 1:

It's quite likely that this issue is caused by hardware (a failing GPU, most likely) but there's a possibility that it's caused by software.

To figure out where the problem lies, boot your computer into a clean install (either Mac OSX/Linux/Windows on a bootable drive, or use your "install Mac OS" install disk/partition). If you experience any kind of problems while using a clean install of any OS, you know the problem is hardware.

You should run a backup as soon as possible, then replace your GPU (Guide) (or take it for a repair). Only attempt to repair it yourself if you completely understand the instructions, if you're unsure, a self-repair may cause more damage

If there are no problems while using a clean OS, the easiest way to fix the problem would be to reinstall Mac OSX; remember to backup your files first so you don't lose anything.

Solution 2:

Backup first! Copy all your essential files, and make a Time Machine backup if possible.

It can be about software or hardware, it's hard to say.

I would first recommend creating a new user account and try there.

Then, reset NVRAM and SMC and try if that help.

The last good solution is Safe Mode and cleaning cache with apps like CCleaner or CleanMyMac.

The bad solution is just installing Mountain Lion on the same partition without cleaning your old system. If that doesn't work, upgrade to Mavericks and try. If that still doesn't work, you might need to do a clean install.

[EDIT: You can also just install to an external drive.]

Please remember to backup your Mountain Lion installation app if possible, or you might need to find is somewhere else later.

If all those above doesn't work, you might have to send it in for repair.

EDIT: Try BootCamp and run a benchmarking tool which pushes your CPU and/or GPU to the limit. That will show if it's a hardware problem.

UPDATE: Check out this Apple Discussion Thread, there's apparently people having problem like yours.

There's also a guide to testing your memory, something you can do if you want to.

Solution 3:

Installing the system from scratch isn't the best case. What I would recommend is if you have a spare external drive. Give it a partition of 25 GB or so and install an OS on it. Do not transfer any files into the new OS on the external. Instead you can open several applications (Grapher.app) and try to stress out the GPU and CPU through an external system. If the issue reoccurs then you are looking at most likely a GPU/video card issue some rare cases MLB.

If the issues don't come up then you most likely have a software issue or corrupted HD. If you have the DVDs that came with your mac then inserting the disk that has the Apple Hardware Test (it is printed on the disc) and boot the computer holding D. This will boot the iMac into Apple Hardware Tests and you can perform an extended test sequence.

Worse case you try an external system or AHT and the computer freezes or corrupts the video. Any AASP or Apple Store has more diagnostics tools to help troubleshoot. Be warned/advised There is a limit to how long a unit is eligible for service and how long parts are available so if the iMac is worth a few hundred bucks take it in to get checked and fixed. Before going in though, please have a backup all the files you need. I have over 6 years experience as Apple Certified Mac Technician so if you need any further clarification please let me know. I am being brief but as accurate as possible to make sure you waste as little time as possible.

Solution 4:

Speculated diagnosis:

I have seen this happen in quite a few macs since the switch to Intel architecture. Like what some others have suggested, I believe this is 90% most likely the initial stages of hardware failure (your GPU), and is directly related to cooling issues. In my experience, no amount of fresh-installing or hard drive replacing is going to fix this.

It is interesting to note that this is occurring on your NVIDIA hardware, as I have usually only seen the ATI chips fail. The cause behind this could be a flawed/abnormal manufacturing process or could be due to improper heat sink seating or inadequate thermal paste.

Unfortunately, it looks like you are going to be due for a repair soon. Your options there are either to replace the entire logic board (as others have stated, the GPU is soldered on), or have it repaired or "reflowed", a process where the logic board is removed and heated so all the solder melts and re-flows in an attempt to fix any shoddy contacts.

Possible fixes:

There are a couple band-aid type solutions you can try that I have had luck with in the past. Firstly, download a fan control app such as SMCFanControl, and set your fans to run at 100% all the time. It makes the machine noisier, but helps keep your mac cooler and more often under that magic threshold of it going berserk (on my old MBP it was 160F).

The second solution is to take the machine apart and re-apply the thermal paste and re-seat the heatsinks. It can be difficult if you haven't done that type of thing before but it is rewarding when it all comes back together. Obviously if you can afford it, it's best to take it to a repair shop (apple-approved only please!) and have them do it. They should only charge you about an hours' worth of labor and maybe a dollar or so for the drop of thermal paste they use.