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

Re the yellow tint... My screen has a distinct yellow tint for about a second after waking from sleep, but then it corrects itself. I always thought that that was the gamma setting being way off and then being corrected. Have all of you with this problem tried playing with Colorsync and seeing if you can make it go away?

Mpat, my yellowtint was permanent. Even with corrections, it was obvious that it was "behind" the screen. I think a loose part or something that makes the screen bleed (hot spot maybe..don't know). Apple didn't even ask, just replaced that one.

i7Mac (W89465)

Arrived Yesterday afternoon, so far so good, came out of sleep this am still fine. Will shutdown later to bring home from work. Just lucky, no shipping damage or Gremlins fell out during their long voyage ?

Man ! ! ! ! I made a good decision. . . Whoa!

There is some sort of pattern, actually: there is a very high incidence of repeat failures. This is a high-profile launch that is widely enough covered that a display smashed in handling gets headliners, yet this problem isn't reported elsewhere. That implies that the problem isn't very common - it's not like it's a 50% failure rate or something like that, probably not even 10%. More likely it's 1% - which is still very high, don't get me wrong - yet a number of people get repeat failures. If the rate of failure is 1% and everything were equal, the chance of two bad machines in a row is 1 in 10000. The chance of three bad is 1 in a million, and so on - yet we have several people in this thread with repeat failures. That limits the possibilities to:

* Environment: hot or cold, humid or dry, especially dirty power, etc.
* Software or usage patterns: More specifically, which apps you run, extra drivers installed, etc.
* Distorting factors: This could be Apple accepting a return, testing it for an hour max and then shipping it back out to someone else who has complained. Since the problem is very intermittent, this is actually a quite likely possibility early in the lifecycle of a problem, but it's something you'd think Apple would pick up on soon enough.

Any other ideas that might account for the repeat failures?

If it's 1 in a million, i'm the unluckiest guy in the world.

Hi - I just took delivery this morning of a brand new 27" iMac Quad Core i7 with 8GB RAM. I started getting intermittent black screen - like it went to sleep, but could not wake it up - then it would come back to normal and flick back to black every now and then.

I performed a restart after removing the power cord for 20 secs, then reset the PRAM, then performed a short hardware test with no problems reported.

After calling Apple Tech Support, they suggested it was a software problem and got me to perform an extended looping hardware test which takes about 5 hours minimum to diagnose. About 15 minutes into the test, the screen started blacking out again so I called them back and told them it was definitely a hardware problem with the screen as I could plug in my second monitor and view use the computer with no issues.

What annoys me is that I advised him that I had read this forum and that it seemed it was a common problem, but he said he had never heard of this problem before! I would have thought - given it has no appeared in the Age website (http://www.theage.com.au/digital-life/computers/flickering-screens-plague-new-im ac-owners-20091126-jtnx.html?autostart=1), that they HAD heard about it now!

A Sydney user has reported the following:

Guess what? It comes down to the ATI Catalyst driver. I've seen the exact same issue on my, and many other clients, PCs, never seen it on my nVidia powered Mac. It's a common enough problem that with my ATI card and Catalyst drivers, my screen will flicker and go black for a few seconds before coming back on. I get this on boot and when it wakes from sleep, exactly the same as what happens on the iMac.

Peter

Thank you for your post, Peter.
I'm sure that will be a very useful nugget of information.

Seems like it is a video card driver or bios issue. Found this solution from the PC side:

http://www.tomshardware.co.uk/forum/page-273975150.html

Does anybody know how to lower the RAM speed to 900 on the card on the Imac? It may solve the flickering and the blacks.

Not saying that too-high memory speeds aren't the problem, but the Mobility HD 4850 (what's in the iMac) has a default memory speed of 850MHz. It's possible that it's clocked higher in the iMac for some reason, but I'd be surprised. The Tom's Hardware link you posted is speaking to the desktop GPUs -- which isn't to say that the notebook parts couldn't have the exact-same problem -- but the notebook parts should have lower clocks than their desktop counterparts by default.

Still, if there was an easy way to lower the iMac video cards' memory speeds, we could quickly test your theory!!

Message was edited by: Schwa72

I have had my machine now for 3 weeks, turn it off some days and some days leave it on others and have not had any issues with flicker. My question, is it because I have the iMac plugged into a uninterrupted power supply and conditioner. I know from experience working on copiers, computers, electronic equipment that if the voltage fluctuates you can get some pretty bazaar issues. HD TV's will give you a bad picture if you have line noise, dirty power or voltage fluctuations. Non of the posts have mentioned the set up of the computer and all have the same type of issue. Some posts have mentioned taking the computer to a specialist and the issue does not appear at that location but happens when you get it back home. Just food for thought.

Message was edited by: Michael Greco1

I am having an issue with my new i7 iMac as well. My problem is that whenever I allow the machine to go into sleep mode (or turn off) for an extended period of time such as overnight and the machine's temperature drops to the ambient temperature of the room (about 72 to 75 degrees fahrenheit, not an icebox by any means) when I turn the machine back on there is a big red "bar" that runs from the top to the bottom of the entire screen about 3 to 4 inches in width that is like all of the pixels are displaying full red instead of any other color.

the really strange thing is that this "bar" only appears in parts of the screen that are supposed to be black, all of the other colors are fine, and it flickers as well (just the red bar, not the whole screen)

after I let the machine "warm up" for about 10 min and the cpu temp gets to about 43 degrees Celsius (based on my temp monitor) the problem goes away and doesnt return unless the computer gets "cold" again.

Is anyone else experiencing a similar problem? Has anyone contacted apple about a similar issue? if so I would greatly appreciated what your symptoms are, how you are dealing with it, and what apples response was if any.

Thanks a bunch everyone, sooner or later apple will take care of all of us and we'll be glad we have these beautiful powerful machines.

Mike:

The UPS was my first thought. I have several Macs and I'm thinking of getting a iMac I7 quad, so this is a problem that interests me. The randomness of the flicker and screen blackout would be symptomatic of a voltage fluctuation. I run all my computers on 3 UPS's, 2 of which have voltage meters. You wouldn't believe how much the voltage varies, from 125v at night to 115-120v during the day. During brownouts you can hear the UPS kick-in and save the day. In reading this thread I have not come across a single person using a UPS with their 27" iMac. I must admit I didn't read every single post, two pages was enough. I'd like to see one of them try a UPS and report back.

John