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Dealing with Dead Pixels in TFT Displays- 23 March 2000
Charles W. Moore
An all too common annoyance to users of computers with Active
Matrix Thin Film Transistor (TFT) Liquid Crystal Display (LCD)
screens is the dreaded "dead pixel" phenomenon. The problem is that, for instance, the 14.1" monitor that has been
used in most WallStreet and all
Lombard and Pismo
G3 Series PowerBooks has a standard resolution of 1024x768, which
means that each of these screens has 786,432 pixels. Each pixel on a
color TFT monitor requires three "sub-pixel" transistors; one for
each color in the Red/Green/Blue color spectrum, which works out to
2,359,296 little, bitty transistors in one PowerBook 14.1"
screen. Now, while it is possible to build TFT screens in which all the
pixels work perfectly (for example the 12.1" screen on the WallStreet
233 I'm typing this article on is "pixel-perfect"), it is impossible
to guarantee 100 percent perfection in all those millions of tiny
transistors while keeping the price of the product affordable. Apple has addressed the dead pixel issue in a Tech Info Library
article, PowerBook:
Pixel Anomalies on Active Matrix LCD Panels. Apple says that a pixel becoming stuck either on or off is known
as a "pixel anomaly," and that it considers a small number of such
anomalies to be acceptable. "The possibility of having a bad
transistor out of a total of 2.3 million is there," the article
notes, "and any bad transistor will result in a sub-pixel
anomaly." The article continues: - "Due to current manufacturing methods of active matrix display
panels, a certain number of sub-pixel anomalies (a pixel stuck on
or off) are acceptable. Because the manufacturing yield of perfect
active matrix panels is very low, displays may have some
sub-pixels that are either always on or always off. The cost of
accepting only perfect displays could nearly double the price of a
portable computer using an LCD screen. This is true of all
portable computers using LCD technology, not just the
PowerBook."
Apple advises that if you think your PowerBook screen contains an
excessively high number of pixel anomalies, you can contact Apple
tech support or your local Apple authorized reseller to arrange an
evaluation. However, you should be aware that Apple will not replace a screen
with just one or a small number of dead pixels. I've heard it
suggested that five is the magic number, but I suspect that there is
actually no arbitrary number threshold, and that the location of the
dead pixels, and whether they are scattered or clustered, would
influence the decision to replace or not. If you are buying a PowerBook from a local dealer, it makes sense
(and not just for scouting possible dead pixels) to insist on
starting it up in the store before you hand over your credit card, to
make sure everything is functioning properly. If you do notice a dead
pixel or two, you can surely ask to see another machine if there are
more in stock. However, dead pixels often don't show up until after a
few hours or days of use, so this is not a sure fire means of
avoidance. Dead pixels can also appear as a result of abuse. My son's
WallStreet, like mine, came with a pixel-perfect 12.1" screen, but it
did develop one dead pixel after a friend of his closed the lid with
a Nintendo emulator running. In this mode, the automatic sleep on
close was deactivated and the 'Book got very hot after four hours of
poorly ventilated running -- too hot to touch in fact. That one dead
pixel was the only tangible damage is testimony to the WallStreet's
toughness. Actually, that dead pixel came back to life spontaneously after a
week or two, but would sporadically expire again from time to time
during the four months between the roasting and when the 'Book was
stolen three days before Christmas. It is also sometimes possible to literally massage a dead pixel
back to life. You can try (at your own risk) gently rubbing the
surface of the LCD screen in the location of a dead pixel, which
sometimes will stimulate the pixel back to life. How hard you decide
to rub is left to your discretion. If you cause any damage to the
screen, that's your responsibility. There is also a freeware utility called LCDtest
that helps you test your LCD screen for bad or stuck pixels. This
program cycles through the 5 basic colors (black, red, green, blue,
and white) so that you can determine if and where bad pixels exist by
examining your screen. To use LCDtest just open it up and use the arrow keys/mouse to
cycle through the colors and carefully inspect your display to see if
any pixels are not displaying the correct color. Of course, if you need a test program to determine if you have a
dead pixel, any problem you have in this context can't be too
serious. However, it's sort of fun checking out each color, and
LCDTest won't cost you anything more than a few minutes download
time. You can download LCDTest from <http://www.nearside.com
/EkimSW/LCDtest/index.html> (Note: as we post this story, the Nearside server, which also
hosts Tom Bender's popular Tex-Edit Website, has been offline for a
couple of days. We hope they will be up and running again soon.)
- <this article available in a printer-friendly
version>
Recent Miscellaneous RamblingsRecent Editorials at Low End Mac- Low End Mac gets
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BiographyCharles Moore has been a
freelance journalist since 1987 -- and writing for Mac web sites
since May 1998. His The
Road Warrior column is a regular feature on MacOS
Daily, and he is a news editor and columnist at Applelinks.com. Charles lives and works in Port Hilford, Nova Scotia, on the shore
of Indian Harbour Lake and in sight of the Atlantic Ocean. His
newspaper columns are syndicated across Canada, and he writes
regularly for several magazines, as well as doing Mac website
journalism. Charles has also contributed to MacToday magazine. His current stable of Macs includes a Mac
Plus, an LC 520, a Power
Mac 9500, a PowerBook 5300, and a
PowerBook G3 Series II/233.
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