Reprinted from TidBITS#1007/14-Dec-2009 with permission.
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http://www.tidbits.com/

New iMac Screens Cracking and Flickering
----------------------------------------
  by Doug McLean <doug_mclean@tidbits.com>
  article link: <http://db.tidbits.com/article/10829>
  2 comments

  Almost two months ago Apple announced a series of updates to the
  iMac line (see "New iMac Models Receive Larger Screens, SD Card
  Slot," 20 October 2009). Changes included larger screens (21.5-inch
  and 27-inch displays), SD card slots, and overall upgraded specs -
  most surprising of which were the first quad-core processors to be
  made available in a Mac outside of the Mac Pro and Xserve. At the
  time of the announcement, Apple noted that the i5 and i7 quad-core
  models would be shipping later than the rest, in November 2009.

<http://db.tidbits.com/article/10664>

  As eagerly awaiting customers have begun to receive their shipments,
  a disconcerting trend of cracked screens and problematic displays
  has emerged. A thread on the Apple Support Discussion forums
  discussing the problems has received over 32,500 views and nearly
  200 responses - significant numbers that indicate widespread
  affliction. Yet, user forums are often difficult places to
  synthesize information regarding problems like this, as specifics
  are generally muddled within anecdotal paragraphs. Thankfully, the
  Apple iMac (Fall 2009) Issues site (hosted on the anonymously run
  imac.squeaked.com) has brought clarity and analysis to the cases
  presented in the Apple discussion forums.

<http://discussions.apple.com/thread.jspa?threadID=2235367&start=0&tstart=0>
<http://imac.squeaked.com/results.php>

  The iMac Issues site disclaims that "The data presented here is
  based on information submitted by people on this Web site or taken
  from comments posted in Apple's Discussion boards (this is an
  'unscientific' survey and as such should not be considered
  representative of all iMacs sold)." Be that as it may, it does help
  clarify the available data.


**Looking at the Numbers** -- While a cracked screen is a more
  startling problem and makes for a more arresting story (and,
  fortunately, an easy replacement), most users complaining about
  their displays are in fact affected by poor video output. Of the 482
  cases logged by the iMac Issues site, 71 were related to cracked
  screens while 225 revolved around flickering displays. Other
  symptoms listed include a yellow-tinted screen (often appearing as a
  band on the bottom portion of the screen), dead pixels, and an
  inability to boot. Descriptions of display issues also include the
  appearance of the display tearing or splitting, or of its image
  becoming offset and distorted. 78 users are counted as having
  absolutely no problems.

  Affected systems are far more likely to be one of the 27-inch
  models, especially when concerning instances of broken glass. Of the
  405 cases identifying some kind of problem, 374 involved a 27-inch
  iMac, while only 31 involved a 21.5-inch iMac. When the problem
  identified is broken glass, all of the cases involve a 27-inch iMac.
  While it makes some sense that the larger model's glass is
  disproportionately affected because its extra screen space makes it
  that much more vulnerable during shipping, it's harder to explain
  the discrepancy between the video output issues, unless the numbers
  simply reflect the 27-inch model's popularity relative to the
  21.5-inch model.


**Examining Causes** -- No definitive conclusions have been reached
  regarding the causes of these problems. Especially mysterious is
  that in the majority of cases with broken glass, the packaging
  appeared unscathed. We assume the computers are going into their
  boxes in good condition, which leaves either excessive fragility or
  issues with transport and packaging to blame. With the packaging
  itself usually showing no signs of distress, figuring out exactly
  what's happening inside the boxes en route becomes a puzzle.

  As for the flickering and problematic displays (videos of which can
  be found on YouTube), suggested causes, or at least avenues for
  further investigation, include high computer temperatures, defective
  power supplies, incompatibility with AirPort base stations, and an
  issue related to brightness settings - dimming the monitor appears
  to reduce the symptoms. Yet for all the speculation, consensus on
  the issue has yet to be reached.

<http://www.youtube.com/watch?v=3jWlepBzVMs>


**What You Can Do** -- If you are affected by the screen flickering
  issues, be sure to contact Apple, either online or by working with
  an Apple Genius at a retail store, to ensure your problem is logged.
  Also consider adding your experiences to the ongoing Apple
  discussion forum thread linked earlier or submitting your data to
  the iMac Issues site's survey.

<http://www.apple.com/feedback/imac.html>
<http://imac.squeaked.com/submit.php>

  For those with broken screens, Apple has been replacing these iMacs
  without hesitation - though a few unfortunate customers have
  received replacements that were themselves broken. If you have an
  Apple retail store nearby, consider seeking your replacement there
  until this issue is resolved.

  We hope to see Apple address what are clearly serious and widespread
  problems quickly and fully.

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