iMac Freezing

As already stated, I got a replacement of the 7600GT (first repair) and then i got a new logic board and another new 7600GT (second repair). None helped. But the service guy told me the parts he is able to order are all refurbished. You will not get new parts as replacements. But since no diagnostig program (even the official from apple service) ever found a hardware problem with my iMac, I wonder if my replacement parts were checked by the same software and declared "OK", even if they are not.
My iMac is now at the apple service center the third time. Let's see what happens now. I really need that machine to work.

Zachnap wrote:
..... Of course, we can barely get anyone to make a post at GetSatisfaction.

I have no knowledge of that site, is it more than just a forum where people can moan about problems - I mean does it actually achieve anything, is it regarded as an official channel for feedback?

I know Apple rarely respond on these discussion boards, but they are monitored and you'd think a thread this big that's not been deleted would have been noticed - it's hardly good press for Apple.

AC

Message was edited by: Alley_Cat

AC, Apple looks at that site. We also want to move this discussion off the Apple message boards so that it gets more exposure. We posted a link right to our section and it is really easy to sign-up for - took like 15 secs.

GetSatisfaction is ok. Podcast actions are ok. Every propaganda we can get is ok. I have signed on GetSatisfaction and petitionspot (?). But as long as Apple doesn't kill the whole thread I prefer to leave the discussion here. I believe that it does more harm to Apple here, within their own site.

As another example: This morning, my iMac froze when I was doing a hard-drive verify in Disk Utility (not very graphics intensive). On the other hand, I can usually watch Hulu without many problems (aside from weird graphics artifacts occasionally).

It very well could be only the graphics card. The heat produced from doing other tasks may "aggravate" the graphics card, and then lock up the computer. Maybe people who had their cards replaced either got faulty cards or they were installed correctly. Seems suspicious, though. I'm still not sure.

zach,
sounds more like an isolated hard drive issue. it could be indirectly related to the freezing/shutdown issue in that numerous hard reboots damaged/corrupted your hdd. have you run any hdd diagnostic tools like drive genius or disk warrior (surface scan as well as integrity check)? is spotlight indexing or time machine backing up while you're emptying? are you doing a simple empty or a secure empty? does the trash contain a few large files or thousands of small files? have you tried using a third-party app like cocktail or onyx to empty the trash?

Haven't tried any of that stuff. It works fine when my Mac is first rebooted but after a few hours starts pulling that stuff. I can't really buy any of those programs right now, especially for a computer that could die any day.

I guess I have a HD problem now too. If my comp stops working I am completely screwed cause I can't buy another one and I need it to look for work - also have no way to back-up any of my stuff.

Could be due to constant hard reboots. Mac *****, I am going to build my own next time I need a comp.

Message was edited by: Zachnap

null

I put the HD fan direct to graphic card and I feel better the sistem stability. Less horizontal lines and now I can open graphics apps.

http://tyc314159.wordpress.com/2009/08/12/refrigerando-el-interior-del-imac/

tyc314159 wrote:
I put the HD fan direct to graphic card and I feel better the sistem stability. Less horizontal lines and now I can open graphics apps.

http://tyc314159.wordpress.com/2009/08/12/refrigerando-el-interior-del-imac/

LOL. Everyone has to check this out. What in the world is going on in that picture - is that a flux capacitor you have hooked up to your iMac?

What's odd about these freezes?

More often than not the cursor still moves around the screen for me.

Think about it.

Now, it's possible that the cursor is a hardware cursor, and that as you move the mouse the CPU updates cursor co-ordinates by writing to specific GPU registers, and the GPU updates the cursor overlaid on the desktop image.

Presumably, there'd also be a cursor bitmap, which in the case of a spinning beach-ball might need updating to animate it.

So, I'm thinking, the desktop image has frozen and isn't updating, but the cursor still updates.

To me this implies that the GPU hasn't crashed, but that the part of the display driver which updates the GUI has crashed - perhaps in response to an error from the GPU, but if the driver can still update the cursor, then clearly the GPU is responding.

So maybe the crash is related to a GPU error or timeout of some action which the OS X driver fails to handle gracefully and hangs.

Everything is working except for the routines that update the main screen display.

If I connect to a frozen machine via VNC the screen display is also frozen or black.

The underlying machine is still active.

It still appears on the local network 'Shared' list - I can still connect and browse or login and access any attached drives.

It is still recognised as a shared iTunes library etc etc etc

So, the underlying machine is working, it's just there's no display update.

Coincidences aside I can distinctly remember this problem arose a day or so after after a big Tiger update early last year - could that update have messed up fan control to control GPU cooling, with secondary overheating when stressed leading to premature GPU hardware problems/RAM corruption?

So in essence I think the freezes are a symptom of a poorly GPU, but not actually caused by it freezing - the freeze I believe is a hang of the display driver routine for screen updating which cannot recover from some GPU error state it's not expecting.

AC

AC, nice think work. I'm not sure... My problems were first noticed in Windows (bootcamp). I would get blank screens and pixels everywhere and Windows would notify me that my "system recovered from a serious GPU failure - contact Ati immediately"

As far as my HD issues and waste basket problems, I ran the Disk utility and repaired permissions and the problem went away - there were like 7 bad permissions. I also ran Color Utility and found 2 bad permissions and repaired them.

I'm also experiencing the same problems with a recently purchased defective 24in iMac. I'm pretty sure its a video card problem. The system would only boot up if I remove the video drivers no quartz extreme, if the drivers were installed it would just freeze after the Apple Logo appears.

Anyway I removed the 7300 mxm card and noticed something a bit odd about the heatsink on the card the heatsink directly touches the gpu core but found in between the 4 samsung vram chips are thick white thermal tape that's suppose to give contact to the heatsink base and vram chips. If that was meant to cool vram chips I don't think that would do the job very well. I just think this is how the vram chips die/produce errors after a certain period of time.

I completely agree with Alley_Cat. I've always felt like if I just knew the correct program to kill, and restart I could get the whole system running again (of course, that might not be possible right now without killing everything... i.e., rebooting)

I would guess that Apple might be able to come up with a software fix that could at least "recover" nicer from crashes (e.g., just reset the entire graphics system, and redraw all the windows, without closing anything). However, putting out a fix like this seems to imply that the problem exists... which Apple might be reluctant to do.

btw... My computer just crashed a couple minutes ago (prompting me to check this thread again). When it froze, the whole screen turned shades of blue! Very weird. The funniest part – when I moved my mouse cursor, it was live, and redrew itself in black+white.

Is anyone thinking that Snow Leopard could make any change?

Bill and others,

First of all, the mouse cursor is not created by the GPU, this is a system level device, not a graphics subsystem device. While it's true that the GPU does the work of displaying the cursor image, the OS handles updating it's position on the screen, the GPU simply draws it based on the instructions the OS passes to it.

So, if your mouse cursor still moves the GPU isn't likely the cause. More likely, another process has crashed. Some external peripheral, hard drive fault, finder crashed etc.

More likely, this is a software issue than hardware. I say that because you said you can access shared media remotely on the hung/crashed machine when you cannot access it on the machine itself. Bring the system up in safe mode and see if the problem continues. If it does, it's probably hardware related though it could still be a kernel level software issue. If it doesn't, it's almost certainly a software issue.