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

Got my 27" i7 iMac, 4gb ram, 2tb HD yesterday.
I'm in Copenhagen Denmark. Its a week 50, with no broken glass, flickering, dead pixels or yellow tinge. In short: it's pretty awesome. So far so good. Will report back if anything changes.

On a sidenote: the mouse had glue stains on it, which I was able to wipe off with a clean cloth. At first I thought it was scratches. Though its a small thing, it struck me as kinda dissapointing for an Apple product.

Hi,

I read your good analysis and *'value drifting'* theory that ATI calls 'dynamically adjusting' on user scenario.

Just take a look on the ATI Radeon 4800 specs :

http://ati.amd.com/products/Radeonhd4800/specs.html

Sentences like : 'Content-adaptive de-flicker filtering for interlaced displays' or 'Clock and memory speed throttling' and 'Dynamic clock gating' make me think that, in fact, some GPU parameters are adaptive ....

It winds up that an event or a context is kinda *triggering the value drifting that the 'sleep-wake' maneuver resets to default* (as does 'reboot' or 'PRAM reset')..

In my case, this 'idiosyncrasy' is rare (4 times in 29 days) and always fixed by a 'sleep-wake' cycle (which in fact is coherent with the theory above : resetting GPU context). With this 7 days period of the 2 seconds issue (flicker-sleep-wake), I could stay cool enjoying my iMac 27" but I can't say yet if the Dec 21 fix was the good one.

A question remains : what triggers the value drifting ? Can't be pure quantum random?
Maybe a close environment interaction (wifi -remember early 2008 iMac and Radeon 4850-, power line quality, wall outlet, frequency, voltage, bad grounding ….) with a subsystem in fragile equilibrium.

Upon doing a software update I noticed this:

http://twitpic.com/usc9a

Perhaps this may be the solution we have all been looking for!

Installing now so will keep you all updated

Jamie,
Folks have been working with the update for two days now (see many, many previous posts in this thread). The update has not helped everyone (the KB article for the update hints that it may not solve the problem).

flickering/tearing has been occuring occasionally (once a day maybe, but not as seriously as some of the ones I've seen online), soi downloaded and installed the firmware update, but i'm still experiencing the same problem. What's the next step?

Have you done a PRAM/NVRAM reset since doing the update? I'm not saying it will work but may be worth a try. Sonics99 suggested that "it may be that the data is still corrupted in the video memory and that is why the firmware is not appearing to fix it" in a previous post. Let us know if it works.

Rick Lang wrote:
THe black screen seems very black, but mine only last a second so one's eye does not have time to adjust to the change in light to see if it's the LCD or LED or both, but my guess is both as I don't recall noticing any 'glow' through the black screen.

Thanks Rick,

I think it would be an important piece of the mystery (and misery for some).
Sonics99, can you comment on this? As far as I recall, you did some extensive testing.

Tom B.

Walker3333 is right, there are two major kinds of resets:

PRAM and SMC. Both of these Apple had most of you perform. SMC if you don't know is the reset where you take all of the cords out of the machine for a minute or two. It is the system management controller. PRAM is your parameter ram and is basically just a part of the ram that is set aside and holds information about how the machine is setup and is held in a battery on the board.

As for NVRAM, I usually reset it in open firmware on boot.
Command Option O+F

"reset nvram
reset all" (no quotations)

As far as I can tell the backlight is working fine. I did the flashlight test and am fairly certain I could see video still for the second it blanked. That tells me it is not the backlight.

Jacques LAPORTE wrote:
Hi,

I read your good analysis and *'value drifting'* theory that ATI calls 'dynamically adjusting' on user scenario.

Just take a look on the ATI Radeon 4800 specs :

http://ati.amd.com/products/Radeonhd4800/specs.html

Sentences like : 'Content-adaptive de-flicker filtering for interlaced displays' or 'Clock and memory speed throttling' and 'Dynamic clock gating' make me think that, in fact, some GPU parameters are adaptive ....

It winds up that an event or a context is kinda *triggering the value drifting that the 'sleep-wake' maneuver resets to default* (as does 'reboot' or 'PRAM reset')..

In my case, this 'idiosyncrasy' is rare (4 times in 29 days) and always fixed by a 'sleep-wake' cycle (which in fact is coherent with the theory above : resetting GPU context). With this 7 days period of the 2 seconds issue (flicker-sleep-wake), I could stay cool enjoying my iMac 27" but I can't say yet if the Dec 21 fix was the good one.

A question remains : what triggers the value drifting ? Can't be pure quantum random?
Maybe a close environment interaction (wifi -remember early 2008 iMac and Radeon 4850-, power line quality, wall outlet, frequency, voltage, bad grounding ….) with a subsystem in fragile equilibrium.

I had suggested this awhile back and still think it is the real issue here. It seems to me that the machine is putting itself into a false state of sleep and get mixed signals of whether it is awake or not. These signals cross and sometimes that results in a quick blackout or sometimes it results in corrupted video because it does them both at the same second.

Great, thanks. I'll try them all and will report back

Sonics99,

Do you mean that the LCD panel content was frozen during the blank?

Tom B.

CliffBell87 wrote:
UPDATE:
Apple corporate customer relations called me today and said I would not be receiving the upgrades on my replacement machine followed by an apology about the miscommunication? The machine is scheduled to ship January 2nd. They are not reimbursing me for my time lugging the machine through the mall, talking to over 6 representatives, and the time I'm spending without the machine. I'm scheduled to make my first payment before I even get a functioning machine? What should I do?

Man, that is simply the worst PR/Customer-Service I've ever heard of (besides outright slander and refusal of service/help). They make an offer and then rescind it??? Wow. Sorry to hear about that Cliff. I was happy for you. Hope things go better.

I've pretty much had enough stress over this machine, so I want to return it for a refund. I went to Apple's online order status and tried to click on return items but it said that I am outside the return period. Has anyone had success getting a return for a full refund outside the return period?

Well, I like everyone else, has verified that the firmware update does NOT fix the issue. Strangely enough I seem to be able to recreate the issue by doing the following things...

1. Use computer all day.
2. Turn off overnight.
3. Turn on in morning - within 90 minutes its flickering.

If I restart the issue does not come back until I've had the computer off for an extended period of time.

Joe