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Miscellaneous Ramblings

Dealing with Dead Pixels in TFT Displays

A 'Best of Miscellaneous Ramblings' Column

Charles Moore - 2000.03.23 - Tip Jar

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 1024 x 768, 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.) LEM

Charles Moore has been a freelance journalist since 1987 and began writing for Mac websites in May 1998. His The Road Warrior column is a regular feature on MacOpinion, and he is a news editor and columnist at Applelinks.com. If you find his articles helpful, please consider making a donation to his tip jar.

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