Q: New iMac 27inch screen flickering/tearing/shutoff

Well, what is happening is that the GPU is crashing, I think that's pretty clear. The question is why it's crashing - that can be hardware, firmware or software.

mpat wrote:

Well, what is happening is that the GPU is crashing, I think that's pretty clear. The question is why it's crashing - that can be hardware, firmware or software.

Indeed, but unless we're engineers and have access to test equipment, we're not really going to solve it no matter how often we debate all the theories. Our role has been to report the symptoms - which I think we've done. As no user has been able to repeat them at will, all we can do now is either return (keep returning) what isn't working properly and wait for Apple to solve it, or, believing it to be firmware, wait until Apple comes up with a fix.

mpat wrote:
Well, what is happening is that the GPU is crashing, I think that's pretty clear. The question is why it's crashing - that can be hardware or firmware or software.

Nothing I guess...
My i7 (delivered on Monday) and is still running beautifully:))
BTW,,, it is 947 series...
PS; Running it 24/7.

mpat wrote:
Well, what is happening is that the GPU is crashing, I think that's pretty clear. The question is why it's crashing - that can be hardware, firmware or software.

I'm not totally convinced that the GPU is crashing. I haven't read all of this thread closely enough...has anyone with this problem also had an external display connected to the Mini DisplayPort at the same time? If so, what was happening on that display while the main display was flickering?

I have read at least one report on another forum of someone having the flicker problem on their main display but also having a 24" cinema display hooked up and working without issue, which would suggest it is the LCD panel itself having problems and not the GPU.

admanimal wrote:
I'm not totally convinced that the GPU is crashing. I haven't read all of this thread closely enough...has anyone with this problem also had an external display connected to the Mini DisplayPort at the same time? If so, what was happening on that display while the main display was flickering?

Yes, I had an Eizo CG241W connected to the iMac 27 via Mini DisplayPort to DVI adapter. Flickering and black outs only happened on the iMac while the Eizo didn't show any problems.

Quick update:
Well, this is a 6'th day and my i7 is still running without a flicker or any other problem...
947... BTW;

pors wrote:

Yes, I had an Eizo CG241W connected to the iMac 27 via Mini DisplayPort to DVI adapter. Flickering and black outs only happened on the iMac while the Eizo didn't show any problems.

Doesn't that suggest a hardware problem after all?

We've had reports of an external Apple Cinema Display 24" flickering in the same way, though. It's useful info, however, and perhaps the issue lies in the part that generates the DisplayPort signal. Older designs used LVDS signalling internally and a DVI signal externally. With DisplayPort, it's the same signal internally and externally, except when a DVI adapter is used. The DVI adapter forces the GPU to generate the DVI signal as well, and it seems to do that better. Very interesting - it makes slightly more sense now.

you and MontanaProducts
posed the same question,... Who knows I suppose,... the one here I7 27 864 has no issues without Ups or surge protector in an industrial envionment 115-123 or so by my reader ( non conditioning only a line meter with paper recorder ) , sleeps, wakes and starts fine. only been two days so we will see.
I personally think its a labeling problem or at least if Apple would attach a $2.00 shock label ,then we could eliminate that as a root cause.

Any reports of this issue occurring on models with the Geforce 9400M? If it's a panel failure, there should be.

So my replacement 27" iMac i7 has arrived. Restored from Time Machine and up and running. Week 48 model. No signs yet but still early days. Will let you all know how it goes.

I have it plugged into a surge protected board, but nothing fancy.

I have received the i7 imac 4 days ago. The flickering started when i was downloading garage band loops. After restarting it disappeared and was gone for the day or so. then it appeared at some point again. Just the commonly reported flicker with blackouts. I haven't really pushed the computer to work had yet, but i am worried now even if i did't have the flicker for couple of days it may start again. Do you think i should return it and get the replacement? Maybe get the refund and wait for couple months until the issues get sorted?
I don't want to start panicking but i also want to have a reliable computer as the price is high.

It's my first mac and I love it. What I can't stand is the lack of clear information and some reaction from apple. If they admitted that the problem exists- and it's software related- I would feel happy and wait for some firmware/software updates, but if it is hardware- then i don't feel like sending my computer for repairs a month after I bought it....

I really appreciate some genuine advice

You need to call tech support asap (always the first step in this kind of issue) and get your issue documented. If you purchased at an Apple store, bring it back as soon as you are able. I have had Apple computers for years personally and on my job. They will make it right. Just be firm and persistent. Regards, JL

yeah, the first thing i did- i called the apple and reported the problem. I was told to restart from the disc etc, but the problem is that flickering occurs out of nowhere. I used the computer for 16 hours designing the flash website and it did not show any bad signs running photoshop, flash and some other apps at the same time. The next day it just started flickering and the flicker was gone again....it will take time to determine the problem and i am worried that if i send it out I could get some worse one than i actually have.... Some people reported high pitch noise, some mentioned the hard drive being noisy. My one seems to be perfect- quiet and not even hot- just nicely warm on the top part. I don't know... Normally things go wrong when you least expect them, and the end of the term at uni is coming soon

camereo wrote:
yeah, the first thing i did- i called the apple and reported the problem. I was told to restart from the disc etc, but the problem is that flickering occurs out of nowhere. I used the computer for 16 hours designing the flash website and it did not show any bad signs running photoshop, flash and some other apps at the same time. The next day it just started flickering and the flicker was gone again....it will take time to determine the problem and i am worried that if i send it out I could get some worse one than i actually have.... Some people reported high pitch noise, some mentioned the hard drive being noisy. My one seems to be perfect- quiet and not even hot- just nicely warm on the top part. I don't know... Normally things go wrong when you least expect them, and the end of the term at uni is coming soon

This is exactly the situation I'm in! I did call Apple and the (very nice) lady on the phone was very aware of the problem and said I should just return my iMac. This could suggest it's truly a hardware problem and not a software problem. She also assured me that the problem only affects a minority of the iMacs. Don't know how trustworthy this statement is. I haven't heard of a single iMac user who hasn't had this problem after one week of usage.