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SeSam is Péter Szilágyi, Knowledgebase Expert at Ustream.tv and a student at Corvinus University residing in Budapest, Hungary. This is his playground.

iMac screen freezes caused by faulty hardware

The title basically spoils the ending, but here’s how my dealings with Apple went regarding the freezing iMac.

To recap the issue: ever since 10.6.3 some Macs produce video freezes where the computer remains running but cannot be interacted with. Screen can black out, white out, show stripes or just an endless beachball. The only solution is to hard reset or – occasionally – use ssh to log into the machine and issue a reboot command. The kernel.log is usually flooded with a particularly disgusting GPU dump.

There is a fairly extensive discussion about this problem on the Apple Support Communities board which started in March 201024″ iMac Screen Freezes since 10.6.3 update – pls help!

People in the thread determined that something in the video drivers cause the freezes and that the relevant kernel extensions can be swapped to their 10.6.2 counterparts which stops the lockups. Of course one loses two years worth of video driver updates this way. Regardless, I’ve been doing this for every OS X update since then.

Feeling that I exhausted all available options one day in February I was just fed up enough to exasperatedly email Tim Cook. After all some people did get a reply…

To my huge surprise I did actually receive a response from an Executive Relations representative who forwarded the issue to a Senior Apple Care Specialist. Although the warranty on the iMac has long been expired, they agreed to deal with the case based on the assumption that it is a software problem. I was quite hopeful we could finally find out the cause of this issue together.

Over the phone I was instructed to set up a separate partition with a fresh install of OS X Lion to prove that none of my installed third party software are the culprit. For weeks I was trying to reproduce the freeze on that installation with little success almost losing belief that it would occur until finally it did freeze out on me, classic rainbow cursor style. Logs and system information were gathered and sent over in hope.

Only the reply I got a week later was a major letdown: the engineers allegedly determined that the root of the issue is malfunctioning hardware. I was told that since the warranty had expired they are unable to offer a replacement video card or any other free solution. What’s infuriating about this is that my iMac is an early 2008 model; 10.6.3 came out on 29 March 2010, meaning I was most likely out of the 1 year warranty when I even had the chance to find out about the problem. Along with several others I was sold a computer with allegedly faulty hardware, with said fault well hidden during the time covered by warranty. That, or everyone’s video cards just fried the day 10.6.3 came out…

I seem to recall that replacement programs have been started for much less. Also we are talking about a company with enough cash to buy my home country’s national debt. And I still get to use a computer with a broken video card.

24" iMac screen freeze

As some of the readers probably know I am a proud owner of a 2008 aluminium iMac (model 8,1).

However, lately I am being plagued by a very annoying and – so far – unavoidable issue: during use at a random point the screen just freezes, something like a permanent screenshot. I can’t tell when it happens, can be weeks without it coming up at all or just after a few hours of being switched on. Sometimes the mouse still works but no input is registered. The machine usually keeps running and – for example if iTunes was on – music keeps playing in the background. I can use ssh to log in to the machine as well.

In order to put the machine out of its misery the only solution is a hard reset. (Or issuing a reboot/shutdown command from ssh.)

I can’t really tell when the phenomenon started, could be around the 10.6.3 update.

I have tried the following methods so far:

So far none of the above helped and I am getting increasingly frustrated.

Some users reported that their video card/logic board was replaced by Apple, only there is no store in Hungary and I’m out of warranty… Regardless, I can’t tell if it is a software issue or a hardware issue brought up by software updates.

Update: So far it seems that Time Machine and the Firewire drive has to do something with the freezes. Unplugged it and freezing ceased, replugged as USB and I got a lockup within the day. Doing a long-term test now with no TM/drive.

Update 2: I have installed 10.6.5 yesterday, replugged the TM drive and only this morning I got another freeze. Apparently the patch did nothing to fix the problem. Testing with unplugged external storage once again.

Update 3: OS X just got endless beachballed while no TM drive was present. Back to square one. Apparently I’m not alone either.