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

Warren B........

Good luck when it comes to understanding graphics cards.

The debate over ATI vs NVIDA is as charged as Windows vs OSX, and like just about everyone who posts on the subject, I have my own biases.

The iMac is a bit limited when it comes to graphics cards, and Apple has to consider several factors when they choose a card for those units.
Higher powered, and faster cards generate more heat, use more power, and are generally far more expensive than the most popular cards in use.
Apple has to consider all of these factors when they decide which card to use in their newest models, in a compact design they have to choose one that can be properly cooled when it is incorporated into that design.
On top of that, the fastest card today, may be the tenth fastest tomorrow.

Comparing NVIDA to ATI is like comparing apples to oranges, since each, given equal characteristics, will perform differently on some functions simply because of the design differences.

A slower card with more memory may outperform a faster card with less, and vice versa in some circumstances.

Most of these cards come in both desktop, and laptop versions which are designed to allow for the designs needs in cooling, and power consumption, and the iMac is generally limited to use of the laptop versions because of their compact design.
The MacPro does not suffer those limitations, but is far bulkier, and more expensive because of it.

Both ATI, and NVIDA have had their share of problems when used in some configurations, and both companies have suffered from lack of customer support, and service at times.

Back to the flickering issue, although Apple does seem to be at the center of that problem right now, a little googling will show you that there are plenty of Windows boxes with i7's that suffer from the flickering issue as well, most all of them using the ATI card.

Generally speaking, NVIDA has always managed to outperform ATI in most areas, but over the last year or so, ATI has narrowed the gap, and at times has built a superior card, although it doesn't take long for NVIDA to take the lead again with a new card.

I think Apple always chooses the fastest card, for the best price, that is compatible with their design, and does put the better cards in their more expensive units. They could put even faster cards in their top end units, but that could easily drive the cost up another few hundred dollars, and could cause other performance problems.

And another consideration, there is more to a computer than just the graphics card. A fast card in a slow machine won't give you much of a boost in overall performance, and in reality, even graphics cards that are several generations old are more than adequate for most users needs. For most users, a faster processor, with a slower graphics card is probably all you ever need.

If you are a gamer, you need a better graphics card, and should choose a unit that can be upgraded on a weekly basis. If, on the other hand, you actually have a life, and live and work in the real world, the graphics card is not as important.

The only really important issue is choosing a card that works. That is why I made the earlier statement, Any NVIDA card that works is superior to any ATI that doesn't.

The bottom line is, there is more to an iMac than just the graphics card, and all things should be considered when deciding which unit or model best suits your needs.

I also had the flickering screen.
I spoke to the guy who sold me my IMac.
I gave me that receipt to solve the problem.

Unplug every cable from the back of the computer.
(IMPORTANT - EVERY CABLE)
Wait at east 15 minutes
Then replug everything and go.

I did this 4 days ago and since then i saw the black screen only once.
I work on my IMac 7 hours a day and more.

Don't know exactly why it work but i'm happy for now...

Hope this can help some of you.

The very first day I had my iMac plugged in and playing our slide show, it went into flickering mode. It stopped with a mouse motion.

It did it a few more times, but it wasn't too bad. I registered the problem with Apple (got a support number) but I didn't do anything else. Since we don't know the cause, a new machine might do worse.

I've since moved the machine upstairs. Different outlet, still 5GHz 802.11N but very close to the Time Machine (it's so fast I've not bothered to plug in a cable yet, though I will one day soon).

It hasn't flickered since the move 5 days ago.

I'm sure it will come back, but it ought to be clear this isn't a simple bug. There may be multiple causes of the flickering, some hardware, some software, some a bit of both. Household voltage or current, WiFi environments, cosmic rays, sunspots ... lots of factors may be contributing. There may be several fixes needed. Some machines will need to be replaced, others may need a firmware update, others may need a different outlet (though that does suggest some issues with the power supply).

I'm as prone to beat on Apple as the next geek. I do think this will take them a few more weeks to figure out though.

Just received my iMac replacement. W8950 serial. No flickering so far (neither yellow tinge as I can not notice it).

I too have the flickering screen/blackout for 1 second since I got my 27" Core i7 iMac 1 week ago. Serial W8947. . . I tried your fix, and so far, so good, no flickering yet, but I have noted this is very intermittent and I (like everyone else) can't seem to figure out when this will occur, so I just wanted to add my voice (and iMac) to the thread. I'm going to call Apple and report the issue (the more reports, the more likely they will acknowledge there is a problem) I just sold my 24" Core 2 iMac on eBay, and I'm now wondering if I did the right thing!

Komodor,
You say:
"I did this 4 days ago and since then i saw the black screen only once.
I work on my IMac 7 hours a day and more.

*Don't know exactly why it work* but i'm happy for now..."

As far as I am concerned, It did not work!
The problem being intermittent, it could be OK for days and then show up again.
Saying you saw it only once since then, confirms that the problem is still there and that like all of us, you can't say when it will come back.

To me that's unacceptable! These are great machines but also expensive machines!

I pretty sure Apple is working on a solution...I hope they are!

But they should at least acknowledge the problem!
I have a feeling this will not happen until the holidays are over $$$!

_*I think we all are I just got mine and it has flickered four times so far!*_

I have posted before about my flicker/blackout issue here before, but this is something new that may be of interest:

I had my screen saver set to the mosaic pattern with an iPhoto folder of 462 photos. I worked fine for a while, then I noticed it was stuck on a pattern and was "stuttering" rather violently. I don't quite know how to describe it, but it made the whole screen look like it was shaking.

I clicked my mouse and the screensaver resumed (note, the mouse click did not end the screen saver, it just caused it to resume). A second click stopped the screensaver and brought me back to my desktop.

Since unplugging my power cord and plugging it back in several days ago, my flickering has not returned--yet!

Does anyone notice that the their GPU makes noises when they move objects on the screen I think that the GPU is resetting I really hope apple does something about this I need a replacement asap I contacted apple support and hopefully will get a RMA.

Hello again Pazuita,

Thanks for taking the time to provide me with a little more in-depth response to the graphics card issue.

So it sounds like you are saying that even though the Mac Pro has an older card than the high-end i7 iMac with the ATI Radeon HD 4850, the Mac Pro with the Nvidia GeForce GT 120 card may actually provide better graphic performance because it is a faster machine, correct?

If it turns out that the ATI Radeon HD 4850 is the source of the flickering, screen blackouts, screen tearing and/or yellow tinge issues, do you have any inkling of how Apple may proceed? Do you think they might use a different card in the first revision of the i7's sometime next Spring?

I'm not asking you to start any rumors here. I'm just interested in your personal opinion since you appear to be more knowledgeable regarding graphic cards...well, at least more than I am.

Thanks!

Warren Beasley wrote:

So it sounds like you are saying that even though the Mac Pro has an older card than the high-end i7 iMac with the ATI Radeon HD 4850, the Mac Pro with the Nvidia GeForce GT 120 card may actually provide better graphic performance because it is a faster machine, correct?

The HD 4850 is a far superior card to the GT 120. In graphics-intensive programs, the CPUs in the Mac Pros will be bottlenecked by the video card. In other words, in graphics-intensive applications, the CPUs will be sitting around waiting on the GPU to finish its processing before they are able to send more data to the GPU. If you intend to do any gaming, you'd be better off with the iMac vice the Mac Pro w/ the GT 120. Now, throw a GTX 285 in that Mac Pro, and then you're talking.

In designing a computer for graphics-intensive apps (3D modeling, 3D rendering, and gaming), it's important to balance the capabilities of the GPU against the horsepower of the CPU. Unfortunately, Apple's a little behind the times (at least as far as the iMac is concerned) in this area. The i5 and i7 CPUs in the higher-end iMacs seriously outclass the HD 4850, so for graphics intensive apps, the CPUs aren't used to their potential because they're bottlenecked by the GPU. Unfortunately, that's the nature of the beast as far as the iMac goes, but for the vast majority of applications that a Mac user is likely to run, this won't ever matter. Only when trying to run the latest games at the highest resolutions and settings will you max out the HD 4850. However, the iMac isn't a serious gaming platform anyway, so it's really a non-issue. If gaming's what you want to use your computer for, then you're better off building your own gaming PC.

By the way Pazuita, it's "NVIDIA," not "NVIDA."

Message was edited by: Schwa72

Schwa72 wrote:
In designing a computer for graphics-intensive apps (3D modeling, 3D rendering, and gaming), it's important to balance the capabilities of the GPU against the horsepower of the CPU. Unfortunately, Apple's a little behind the times (at least as far as the iMac is concerned) in this area. The i5 and i7 CPUs in the higher-end iMacs seriously outclass the HD 4850, so for graphics intensive apps, the CPUs aren't used to their potential because they're bottlenecked by the GPU. Unfortunately, that's the nature of the beast as far as the iMac goes, but for the vast majority of applications that a Mac user is likely to run, this won't ever matter. Only when trying to run the latest games at the highest resolutions and settings will you max out the HD 4850. However, the iMac isn't a serious gaming platform anyway, so it's really a non-issue. If gaming's what you want to use your computer for, then you're better off building your own gaming PC.

Interesting. So you're saying that -- in your opinion -- the ATI Radeon HD 4850 card is actually outmatched by the Quad Core processors in the i7's, right?

So it would have been better to go with the 4870 -- or even something in the 5800 series -- for better compatibility, and even better performance?

Thanks!

I am finding this discussion educational. It breaks the monotony of this thread a bit.

Been a few days since i got my week 50 replacement...so far so good. One thing i noticed which is probably completely unrelated is my problematic week 47 had a really spongy power button, almost to the point where i couldn't tell if i was pressing it. This week 50 has a positive click when i press it. Will keep everyone updated.

Thanks,
Tony

Warren Beasley wrote:

Schwa72 wrote:
In designing a computer for graphics-intensive apps (3D modeling, 3D rendering, and gaming), it's important to balance the capabilities of the GPU against the horsepower of the CPU. Unfortunately, Apple's a little behind the times (at least as far as the iMac is concerned) in this area. The i5 and i7 CPUs in the higher-end iMacs seriously outclass the HD 4850, so for graphics intensive apps, the CPUs aren't used to their potential because they're bottlenecked by the GPU. Unfortunately, that's the nature of the beast as far as the iMac goes, but for the vast majority of applications that a Mac user is likely to run, this won't ever matter. Only when trying to run the latest games at the highest resolutions and settings will you max out the HD 4850. However, the iMac isn't a serious gaming platform anyway, so it's really a non-issue. If gaming's what you want to use your computer for, then you're better off building your own gaming PC.

Interesting. So you're saying that -- in your opinion -- the ATI Radeon HD 4850 card is actually outmatched by the Quad Core processors in the i7's, right?

So it would have been better to go with the 4870 -- or even something in the 5800 series -- for better compatibility, and even better performance?

Thanks!

I am finding this discussion educational. It breaks the monotony of this thread a bit.

That's exactly right. Especially considering the high resolution of the 27" iMac, the HD 4850 is simply outclassed by the i7-860 in the iMac. As a point of reference, my gaming PC has dual NVIDIA GTX 295 cards in it. Each GTX 295 has two GPUs, so that system has four total GPUs, plus a fifth GTX 260-216 GPU dedicated to physics. Any one of the GPUs in my gaming PC is more powerful than an HD 4850, and even that computer (which also has a 3.73GHz Core i7-965XE CPU) would be hard pressed to max out the most modern games and maintain 60 fps at 2560x1440. The point I'm trying to make is that higher resolutions stress the GPU far more than they do the CPU, so a powerful GPU is extremely important if you intend to run graphics-intensive software at high resolutions.

All that being said, even the latest and greatest single GPU graphics card would struggle with some 3D applications at the 27" iMac's native resolution. But for 99% of applications out there that Mac users would run (read: not games), the HD 4850 is fine. It'll support 1080p video just fine, and it's snappy enough with most run-of-the-mill 3D animations.

Well, I have a related question I'd like to ask you, and everyone here who may be knowledgeable regarding computer graphics cards.

Would running the iMacs below the default native screen resolution do anything to help extend the life of the GPU, the CPU or the computer in general, since it wouldn't have to work quite as hard to draw the screens?

I know that things like videos might not look quite as nice, but is there any real advantage to lowering the screen resolution, insofar as the life of the computer is concerned?

Thanks!