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

Now i spent some time to do some research on google. Check out this:

http://en.wikipedia.org/wiki/Triplebuffering#Double_buffering_in_computergraphics
http://en.wikipedia.org/wiki/Vertical_synchronization

This suggests me (maybe i'm totally wrong, i'm not an expert for sure) that:
1. yellow tinge problem is caused by a manufacture problem with the LCD (and/or also by the shipment)
2. flickering/tearing is caused by firmware/software and, perhaps, by the v-sync cable

User experiences in this thread said:
1. after a replacement of display and/or v-sync cable the problem was fixed
( 1a. after a rep of lcd/vsync problem *was not* fixed ? <= Not sure about this)
2. after software/firmware update the problem *was not* fixed
3. the problem is present only on some units

If there are also problems in the video card hardware:
1. can't be on the VRAM cause we would see images with wrong colors (i mean a pixel instead of be green is yellow) or anyway other kind of issues
2. (Radeon HD 4850 uses double-buffering, check specs) they could be in the process of copying from the front buffer to the back one, but this process (i think) it's software(firmware) controlled

So, since the problem is not widewide spread, we could think *it's not software* related, otherwise (nearly) everyone should have it.

Now, we remain with only v-sync cable and the LCD panel.

As what i have understood from wiki, Vertical Sync is used to avoid flickering/tearing usually in games by preventing the LCD from read the next frame too much quickly and i don't know if it's enabled or not by default in OSX. The tearing/flickering *suggests* it's not enabled or the vsync cable is faulty.
So i'm thinking: what happens if we enable or disable it on a faulty iMac? Does anyone know how to do this or something about on OSX?

This comes out from my thought "if the vsync is disabled, that faulty(?) cable should not logically used and and left in a high impedance state". And this can be easly wrong.

Obviously i know that Apple's Engineers have already thinked about that for sure and if this could solve something they would already fixed it.

Any comment or thought is appreciated.
Don't blame me if i tried to say something of useful based on what we know atm and i failed =)

Salut jc44

I'm just a few streets east of that store.
I live on first Avenue and Bellechasse.

My machine came from the Apple store downtown but if I have to get it fixed, I will probably go to Royal Photo as well.
I have bought memory there before and photography equipment as well.

Keep us posted on how your machine behaves.

Merci.

I forgont one thing:
to try with vsync enabled/disable you could play a game and set the vsync off/on or use any other (fullscreen?) app that gives you the ability to choose.

Ettore,
Good links.
Re watching the video I made earlier, it appears to me that the idiosyncrasy is a rapid blanking (generally 3 times) of a group of lines (like on old TV sets) followed by a blackout (just like an instant sleep mode). I recorded the sound of a relay, when the display blackouts.

A good theory must be coherent with the fact (my experience 100% and others) that the 'display sleep/wake' (1 second with the configured magic mouse) is a regular temp fix for a week or two and sometimes for more than a month : the graphic subsystem has no time to cool down in 1 sec.
The effect is for me a reset a corrupted values.

The hardware/software difference (black/white) is less relevant in complex systems like this.
The GPU (hardware+firmware) is adaptive and tries to follow user profile (OS+drivers).

Jacques.

I agree I will just as I said tell him its been flickering on and off, and am sure it won't flicker for him. Its always like that, as you said! I will tell them they need to test it from time to time to see it flicker. Hopefully they will give me a new one thats flicker free and I can transfer the files, etc, from time machine.

Thanks for the information!!

Mark

Hi all,

It's been a while since I returned my second defective iMac (yellow tinge.) and I'm wondering is it safe to go back out and buy one? Or are there still problems even with Week 02 and above?

All the best,

/s0l

I am going to give it a shot I think the potential of the computer is great and I love the 27in screen. Plus I have a old 23in Mac monitor attached to it, which works well too.

Mac has to come out with an update to fix this problem, maybe I am wrong?

Mark

I have to say that i didn't see all your posts Jacques. Now i read them and checked out the video.

If the display sleep/wake is a temp fix, it is for display and should not involve video card, could this be right?
You heard a relay and the consequent screen shutdown. This suggests me only one thing: overcurrent/overvoltage protections BUT it can't be due to the next week/month problem-free.

I don't wanna continue on the hardware (or we can speak also about LCD firmware?) issue line but it's just a try to see if there are good reasons to say it isn't.

Update: Just got a phone call from Apple. Basically he looked at my Pictures I had sent via email & confirmed there was indeed a Color Variance on my Screen. He basically & very honestly told me this is just a follow up phone call to get more info from me. He then told me Apple does not currently have a fix. They are working on it. He also said, the they were told they may have a fix in 3 weeks. He also said it could take longer. When I asked why Apple never tried a firmware fix for the 21" iMac. He said, at the time we did not know the 21" had a problem. But we do now. I told him I just don't want to keep swapping out iMacs, only to get another faulty one. He completely understood & agreed. He said he or someone else will get back to me when there is a definite fix. He was polite, professional & empathetic to my situation. Bottom line is he was honest. They don't have a fix yet! So I will wait patiently. I feel better now. I also made a joke & said, if it's not fixed for 6 Months, will they upgrade me to the future Model iMac. He laughed & said, No, it will be resolved by then.

Another question: you can hear the relay sound only when it goes black due to flicker or also when you sleep the display?
Cause if this sound is present also when you sleep it, this could suggest that is caused by the video card or something of software that send a ACPI sleep signal. Otherwise (as i think) it's a protection system in the LCD.

one more thought.

do I just get my money back and buy a mac pro? I have a few days to decide?

Any thoughts?

Thanks

Mark

Dino1956 wrote:
Photos: Click On LARGE in MediaFire

http://www.mediafire.com/i/?22wwlojgift

http://www.mediafire.com/i/?vddqdtkdjnm

Hello Dino,

That is about the same degree of yellow tinge on my iMac as well.

BTW, my week 51 also has a Hitachi hard drive -- a 2 TB HD. There are a variety of noises in my room from the air con, aquariums, and other computers, but as far as I can tell, this 27" iMac is very quiet.

Warren, *Read my update above. I talked to Apple.*

Yea, if I'n not playing iTunes, my room is Silent, so I can hear it, but it sounds more luck a soft purring accessing sound. Not loud. Mine is base 21" model NVidia 500 GB HD.

It's really hard to notice Color Variance in Applications or White Screen. But as soon as I put up the Grey Bars, I see it!

Dino1956 wrote:
None of it makes any sense. There is a ton of Misinformation going around. On this thread, In the Media, as well as in Apple Support. I can't see after making this type Model of iMac for so long, how Apple could not have figured out the Problem yet. No software/firmware update in 2-3 Weeks is going to help a Yellow screen. And IMO, if it stops Screen Flicker, it's like putting a band aid on a cut that needs stitches. Just my little Opinion. Of course I'm not an Engineer or an Apple Tech & I could be wrong.

Hello again Dino,

As I've mentioned before, I've had the very same sentiment for quite some time now. I don't understand how Apple can make a beautiful, flawless 24" iMac, and then suddenly begin to have all of these problems when they begin to manufacture the 21.5" and 27" models. What is so drastically different between them, other than different graphics cards and -- in the case of the 27" -- more pixels on the screen? Like yourself, I am not an Apple technician, so I cannot possibly answer this question fully. I am also doubtful that what is coming in three weeks is going to fix all of these problems permanently. Like many here, I get the impression that Apple is stabbing in the dark with these firmware updates. On the other hand, it does seem like the LCD and cable exchange is a more reliable fix . . . at least so far, according to what we have read in this thread.

Jacques LAPORTE wrote:
-Update-

i7 27" week 45

flickering screen returned Jan 28 after 33 days of absence.
Previous occurrence : Dec 26!

Wow . . . I'm very sorry to hear that Jacques. It doesn't give much hope to the rest of us here who are still waiting to see where our machines really stand. I am now on my 10th flicker-free day, but given your current circumstances, it really makes me wonder if I'll still be as upbeat a month from now.