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

DeeJay SchmeeJay wrote:
This has become a massive thread so it would be unreasonable to expect you to read it from the beginning. But I have read this thread from the beginning, and can say you have not brought any new information that hasn't already been discussed many times over. You maybe on the right track, but I'm placing my bet on those who suggest that something is dodgy with the power supply or isolation of the power supply. On your next coffee break read the following thread about an issue with the 24 inch Cinema displays...

http://discussions.apple.com/thread.jspa?messageID=10786900#10786900

There are some interesting similarities.

So if it's with the power supply would simply dimming the display help curb the issue? Has anyone seen a reduction of frequency of flickers, flashes and blackouts as they dim the screen? What could be wrong with the power supply to cause it to do that to the screen? Would the 24" Cinema display have a similar power supply?
I think your hypothesis holds more water because both the 21.5" and 27" iMacs have this flickering problem. If it were just the screen it should just show in one or the other unless its a manufacturer error in new screens.

chonody wrote:
So if it's with the power supply would simply dimming the display help curb the issue? Has anyone seen a reduction of frequency of flickers, flashes and blackouts as they dim the screen? What could be wrong with the power supply to cause it to do that to the screen?

I can't answer these questions but I've been amazed at how power supplies that don't cope with fluctuating mains voltage can cause problems like these. I once had a MIDI interface whose connection would often go haywire around 6pm (while people are cooking dinner causing a power drain in the neighbourhood). The solution? A new power supply. And my current G5 has a TC PowerCore Audio Effects PCI card which refuses to work unless I switch off one of my monitors whilst I boot the G5. This is because the PowerCore Card is not getting enough power during boot up. And these problems have occurred even connected to a UPS.

The Power Supply Unit is the very first link in the chain and it has to be considered as a potential culprit in this situation.

DeeJay SchmeeJay wrote:

chonody wrote:
So if it's with the power supply would simply dimming the display help curb the issue? Has anyone seen a reduction of frequency of flickers, flashes and blackouts as they dim the screen? What could be wrong with the power supply to cause it to do that to the screen?

As far as I recall in some cases dimming (or brightening) the screen was actually triggering the flicker. Also some people reported problems going away with the UPS. But power supply are tricky things and Apple is not talking.

Tom B.

I agree with you. The power supply is most likely the problem. Let's hope that apple can deal with this quickly and without returns.

It seems sensible to register the problem. If nothing else it helps Apple understand how widespread it might be.

I did that myself.

I do agree that it makes no sense to return the machine unless the flickering is very severe. Any replacement might do worse.

My machine had flickering once every other day about 2-3 weeks ago, but since I moved the machine it hasn't flickered (different outlet but same mains power). I didn't bother installing the firmware update -- why mess with it if it seems to be doing well?

Modern computers are so complex I can imagine it might be any combination of several pieces of hardware and software causing the problem, including the bluetooth, 802.11n, power supply, graphics cable, etc, etc. I suspect different machines may have different combinations of precipitating factors.

Bottom line: If the flickering isn't severe, wait. There's no harm in simplifying your machine -- turn off WiFi if you use a physical cable, turn off bluetooth if you have a wired keyboard, etc.

chonody wrote:
I agree with you. The power supply is most likely the problem. Let's hope that apple can deal with this quickly and without returns.

When I took my i7 in for repairs the power-supply was one of the things that they were replacing (along with the CPU fan and the logic board).

FRENZIED wrote:
When I took my i7 in for repairs the power-supply was one of the things that they were replacing (along with the CPU fan and the logic board).

Did that help the flickering any?

Several have commented on the fact that many recent posters have not taken the time to read previous posts, and are again proposing ideas, questions, and solutions that have been previously discussed.

After more than a hundred pages of posts, few of us have the time to read them all, so maybe those of us who have been here from near the beginning can be of help to the newcomers, and try to summarize what has been stated or determined to this point.

The first thing ruled out was temperature, since many units displayed the effect shortly after startup, while cool, and others did not show the flicker until warmed up. Many showed the flicker at both cool and hot temperatures.
Many who were running temperature monitoring software, reported that there was no consistency relating to temperature, and the flicker, effectively ruling out temperature as a source.

I should point out that while the iMac does have sensors in place to monitor temperatures, there may still be hot spots, not detected, such as connections on, and between gpu and display that could cause the problem.

The problem is completely random, and so far, no one has posted that they have been successful in consistently replicating the problem. The ability to create the problem on command is essential in determining a cause.

To this point, the flicker has not caused any data loss, or corruption, or at least, no one has posted that it has.

Putting the display to sleep momentarily seems, for most, to be equally as effective as reinstalling the OS, rebooting, or zapping the PRAM, in temporarily curing the problem.

As many have stated, it is most likely that if the problem was OS related, then it would most likely affect all machines, not just a few.

Location seems to have no affect since posters come from across the globe, in many different countries. Likewise the power supplied to the unit is most likely not the cause, since locations, and suppliers are so varied, along with many using supply protectors, and a wide variation of surge protectors, still have the problem.

The new batch of machines, at least thru week 51 still have the problem.

Several have posted that they have either replaced components themselves, or had components replaced, with little affect on the problem. Components replaced include the graphics card, and display, although it is possible that those items could have been from the same batch as the original, and could have been defective as well.

Apple is aware of the problem, although they have not made a public statement other than stating in the firmware update that the update was designed to address the flickering issue.

The flickering is not limited to iMacs, and many windows box users have had similar flickering issues while using the ATI 4850 on an i7.

To this point, nothing has been totally ruled out, and Apple seems to be as stumped as the rest of us. Since the problem is so random, and intermittent, there is no way to test for the problem, so defective units will probably continue to be shipped until such time as an effective test, and possibly a cure are developed.

Throughout the problem, Apple has remained the leader in the industry with the best warranties, and customer support available.

Any of the other old timers on this forum have any more to add for the newbies?

chonody wrote:

FRENZIED wrote:
When I took my i7 in for repairs the power-supply was one of the things that they were replacing (along with the CPU fan and the logic board).

Did that help the flickering any?

Mine didn't exhibit any flickering (for the short time I had it). It had the yellowish lower half screen, spinning-out-of-control CPU fan and it wouldn't stay awake after being woken up.

I opted to have it replaced and won't get the new one until middle of January.

I've had the same problems as everyone else with my 27 inch iMac, I called and they offered to either have it repaired or replace it. I hope Apple figures this out soon!

I'm wondering if there's any correlation between the number of days the problem takes to appear and the severity of the problem. I sort of get the feeling, from reading these posts, that the longer it takes for the problem to appear the milder it is. Is that true? I used my i5 for 11 days before noticing any flickering and it has only ever been a minor problem (so far) that's easily stopped by a sleep/wake display cycle (using an exposé screen corner) and it goes away for days. What have others experienced?

thanks for taking the time to post that!

Hey guys, just out of curiosity, did any of you have the flickering in bootcamp? i.e. under windows? Wouldn't this tell us if this truly is a hardware or software defect? Thanks

I posted a thread (http://discussions.apple.com/thread.jspa?threadID=2276961&tstart=0) which I talk about my phone call with a Apple tech about this "flicker & blackout" problem. My machine got worst and worst until I was getting an issue many times in a hour. We ended up running extensive diags from the Mac OS X disk and we never had an issue. This in my mind pointed to some kind of driver issue instead of a hardware issue. I found a sequence of resets which I have not had any issues with for days. So you might what keep your eye that thread since I use my I7 27" about 4-6 hours a day. I will try to keep it up to date.

Ver: 10.6.2
Build: 10C2234
ROM Revision: 113-B9110C-425
EFI Driver Version: 01.00.383



Mike

angelswings wrote:
I'm wondering if there's any correlation between the number of days the problem takes to appear and the severity of the problem. I sort of get the feeling, from reading these posts, that the longer it takes for the problem to appear the milder it is. Is that true? I used my i5 for 11 days before noticing any flickering and it has only ever been a minor problem (so far) that's easily stopped by a sleep/wake display cycle (using an exposé screen corner) and it goes away for days. What have others experienced?

Yes and no.
I think the severity is only due to what cause the problem. My iMac shows the flickering the very first day (1 or 2 hours after the first start) and since then I only get it 3 more time in 1 month and only when I did something unusual (turn it off and add memory, Plug a PC notebook on the same UPS as my iMac is, etc.).
So for my iMac the problem is not severe at all and I got it a few hours after unpacking it, but of course if the problem is severe this will most certainly be because the cause frequently occurs and so you must see it very soon.