The New iMac Display Problem?

Discussion in 'iMac' started by Shaun.P, Oct 24, 2009.

  1. macrumors 68000


    Jul 14, 2003
    Omicron Persei 8
    Hello all,

    I have documented this in another thread but I thought it would be better to dedicate a thread to this "problem".

    I bought a new entry level iMac the other day. At night, before putting the computer to sleep, I often put the brightness of my screen all the way down to 1 notch so that when I wake the computer up in the burning the display doesn't burn my eyes.

    So, I did this with the new iMac. When I woke up in the morning to check my email, the computer came out of sleep fine, but the display was flickering. As if it was pulsing between a brighter brightness level and a duller one.

    The problem continued when I increased the brightness to 2 and 3 notches, but seemed to disappear after that. I have been able to recreate the problem many times (it is not intermittent) and it is also noticeable if you shut the computer down on 1 brightness notch and start the computer up a few seconds later.

    I PM'ed someone in this forum who bought the very same computer as me and he was able to recreate this "problem". I was wondering if all of the new 21.5" and 27" iMac users could try the following:

    1. Put your computer brightness down to 1 notch.
    2. Put the computer to sleep.
    3. Wait about 30 seconds.
    4. Wake the computer up from sleep, and focus on some part of the screen.
    5. Does it flicker? Does it disappear when you increase the brightness level?

    I don't know if this problem is that major as I very rarely use my machine on such a low brightness level, but in the morning, when you've just woke up even the 1 notch of brightness can seem exceptionally bright!

    Let me know if you can recreate this problem on your new iMac. I think it could have something to do with the new LED backlit display.

    Thanks in advance,

  2. macrumors 65816


    May 2, 2009
    Its the pulse width modulation of the LEDs. The time between the on/off cycles needed for that level of brightness is so long that the human eye can detect it.
  3. macrumors regular

    Nov 12, 2008
    So is this the same on every new iMac? Just wondering because I am very acute to color change and this would definitely wiegh on my comfort.
  4. macrumors 65816


    May 2, 2009
    Depends on how many LED it has, the iFixit teardown didn't day how many are there. If it has a lot of them to brighten the big screen evenly they would have to be powered pretty low to get dull but even light.
    Smaller devices (like the iPhone) probably don't have the issue because they have few LEDs.
  5. macrumors newbie

    Oct 24, 2009

    I've just gotten the 21.5" iMac and it was last night when I noticed the flickering you described above. Indeed it does happen only in low brightness. In fact, it stops flickering when I increase the brightness to 6 bars/levels.

    I may have found a software fix for this. It's called Shades which is free to use. Basically, it's a software that controls the brightness of your screen independently of the OS X's brightness settings.

    What I did was turned up the system brightness to maximum, then used Shade's settings to turn down the brightness to a comfortable level. See if this works for you.

  6. macrumors regular

    Nov 12, 2008
    my brightness is always set between 1 and 3 notches. if the flickering is as common and noticable as previously posted, I will never be able to enjoy this brand new toy.
  7. thread starter macrumors 68000


    Jul 14, 2003
    Omicron Persei 8
    Hi again,

    If the display has been on for a while and I reduce the brightness down, the problem does not occur, it is only when the machine was woken from sleep or startup.

    I don't think I'm going to ask for a replacement - it is probably software, and this machine is working perfectly fine except for that small annoying problem!

    I love the iMac and I'm sure this isn't anything major to worry about.
  8. macrumors newbie

    Nov 3, 2008
    Jacksonville, FL
    On mine I am noticing that my screen is flickering with a line going across my screen. As if it is about to completely cut off, is this what everyone else is experiencing?
  9. macrumors newbie


    Oct 16, 2009
    Hi all,
    on my new 27" I have probably a similar problem, but I cannot reproduce it yet. Randomly sometime the monitor start flickering and, in some cases, become black for some instants.
    Until now I get the problem few minutes after startup (after a night with the imac shutdown).
    Initially I was thinking it was an hardware problem, but if I restart the problem disappear.
    What do you think about it? Do you think it could be a software problem?

    UPDATE: I get the problem with brightness at about 7 notch (half)

  10. macrumors 603


    Apr 1, 2009
    15 minutes in the future
    Does not happen on my 17" macbook pro.
  11. IMAKEAPPS, Oct 24, 2009
    Last edited: Aug 16, 2012

    macrumors newbie

    Oct 24, 2009
  12. macrumors 65816


    May 2, 2009
    Nobody ever said your model had the issue.
  13. macrumors 68030

    Jul 5, 2008
    Thule GL @ the TOW
    ...get another replacement, he didn't build it = thank China and the US labor unions...
  14. macrumors 68020

    Sep 27, 2008
    Don't sweat it, this guy's a troll...
  15. macrumors 6502

    Jun 25, 2006
    LMAO! The random conversation of the day.
  16. macrumors member

    Jan 28, 2009
    Im not getting the flickering problem but i am getting another display problem.

    My screen is not coming out of sleep basically. If I put it to sleep and wake it a few seconds later it comes on fine but if I leave the machine for a period of time and the display turns off by itself it wont turn when I press the mouse or keyboard. The imac is still running fine because my itunes still plays, its just the screen wont turn on. I get the same problem if I set the iMac to sleep at night and when I turn it on in the screen and have to reset with the power button.

    This is with the base 27".
  17. macrumors 6502

    May 27, 2007
    Montreal Canada
    I don't have an IMac but I have an anecdote that might help you.

    Back when I first got my MBP (and was still in school), I noticed that the screen would flicker only in a particular classroom. I would always have my brightness to a minimum as to conserve battery power.

    I turned off the auto-brightness sensor in (System Preferences -> Display) and it stopped flickering. It seems the lighting in the room was precisely on the threshold of the sensor.

    Try it out on your new imacs and see if it solves the flickering.

    Good luck :)
  18. macrumors 68040


    Jul 30, 2007
    You must compute in a photography dark room. :p
  19. macrumors member

    Aug 4, 2007
    Yeah I got the same problem but I usually keep my brightness high so its not an issue
  20. macrumors 6502


    Oct 25, 2009
    I had a flickering problem with my 27" as well.

    It was impossible to reproduce. I could work for hours on the computer and then suddenly it would flicker randomly with a band of horizontal static bars about 3 inches thick momentarily or, alternatively, it would black out for a fraction of a second. This could happen up to once every 5-10min.

    My previous iMac 24" had a display freeze problem that was impossible to recreate and ended up being solved with a firmware update. Hopefully that's the case - it would be unusual for so many to have a common hardware malfunction, unless there is a fundamental design problem.

    I noticed the problem within 24 hours of buying it, so I returned it to the Apple Store. After some time talking to the manager, the store was reasonable enough to accept it as a refund with no restocking fee despite being unable to reproduce the problem.

    It's a shame, b/c the computer is so nice. I was considering getting the quad core, but if this is a more common problem, I may have to hold off. Dammit - I was hoping I just had a lemon. :(
  21. macrumors member


    Nov 16, 2008
    Screen flicker on new iMac 27 :-(

    I received the new iMac 27 before the weekend, and have spent many hours during the weekend to play with it, and transferring music and stuff from my old 24 iMac.

    I've noticed that the screen sometimes flicker or show some weird glitches / graphic (sometimes purple - or white with a bunch of lines or weird graphic)... this happens sometimes when I play a youtube clip or in safari when I scroll or make a new tap - or does something where the image on the screen changes...

    I'll try and see if I can capture it on video - but do you guys think its a software error, or the screen that might have a problem?

    I've done a fresh install but the error still occurs from time to time.

    I also have another question - about upgrading the RAM. I have two 2GB sticks I bought from Crucial for my Macbook Pro 13 - would it be okay to mix these with the current two x 2GB already in the new iMac?
  22. macrumors newbie

    Oct 26, 2009
    Screen Flicker on 27-in

    Two and half days with new 27in -- screen flicker variable in frequency and intensity (usually white flashes pulsing across the screen). Today, went 8-10 hours without noticing it. However, as if in anticipation of reading this thread, it began happening, randomly.

    I have a 24in Apple Display (DVI with adapter) running along side it in extended desktop mode. While this 5-year-old gem now looks dull and pale next to the 27-in glossy monitor, it nonetheless stays rock-solid during the bouts of flickering encountered on the IMac screen.
  23. macrumors regular

    Aug 4, 2009
    I wonder if the pulse rate is more noticeable under fluorescent lights.
  24. C64
    macrumors 6502a


    Sep 3, 2008
    Q about this problem: Is this purely hardware or something software-ish?
  25. macrumors newbie

    Oct 26, 2009
    Well...this is disappointing im having this problem too, my screen is just randomly flickering. It doesn't always happen, not only that but the screen will randomly restart too. I have a video of it, ill post it soon.

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