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LCD screens are one of the most expensive parts of a PDA.  They're also the most likely part to contain noticeable flaws in the form of the dreaded dead pixels.  Each PDA manufacturer has their own policy on how many dead pixels warrants a return and replacement.  The problem is, most people are not aware of this policy before they get their PDA and falsely assume that one dead pixel is good enough to ask for a replacement, but this is generally not the case.

Some Background on LCD TFT Displays

LCD stands for Liquid Crystal Display, it is the type of screen used in every PDA you can buy on the market these days.  Screens come in various sizes and resolutions.  Resolution is defined by the number of pixels (small dots) that make up the LCD screen.  The pixel is the smallest unit that makes up an image.  A pixel is however sub-divided into three sub-pixels colored red, green and blue that work together to display the correct color for that specific pixel location.  Nearly all screens sold today are TFT (Thin-Film Transistor), TFT is also known as active matrix display.  A TFT display means that each sub-pixel has a transistor, having a transistor at each sub-pixel means that the current that triggers illumination can be smaller and therefore be switched on and off more quickly.  This means a TFT display is responsive to change, so when you move a cursor across the screen or a fast moving image is displayed the TFT display is fast enough to reflect the movement (with a passive matrix display, the image might temporarily "dissapear" until the display can "catch up").

So What Causes a Dead Pixel?

Occasionally the individual transistors responsible for carrying current to a pixel will either short out or remain open resulting in what is called a dead pixel.  A "lit" pixel is one that appears as one of several randomly placed white, red, blue or green pixel elements on a dark background, or you may have a "missing" pixel which shows up as a black dot on a light colored background.

So Why do New Screens Have Dead Pixels?

During the production process of LCD screens it is difficult for manufacturers to assess if a pixel is out or not.  In fact, only once an LCD panel has completed production and assembly can it be determined that an LCD does or does not have dead pixels.   Material costs are high for LCD displays so every attempt is made to avoid scrapping displays.  If a screen is determined as being overly flawed, it will be thrown out, but if the screen is within a set quality standard -- say 2 dead pixels -- then the screen will not be thrown out.  If manufacturers had to throw out every screen with even 1 dead pixel, prices would be much higher for LCD screens.

But What is the Standard Regarding How Many Dead Pixels is Acceptable?

This question is what we're really concerned with here.  If you're spending $400+ on a PDA then you as a buyer of course would prefer zero dead pixels on your screen, but you're probably willing to accept the fact that one stuck pixel in the corner that's only noticeable on a dark background will not warrant a return and is likely not worth the hassle.  But what if you have three dead pixels, does that warrant a return?  You would hope so, but that's not the case with many manufacturers.  The number of dead pixels it takes before a manufacturer will accept a return varies, and some manufacturer return policies for dead pixels is downright complicated.  In general, most PDA Manufacturers will consider three dead pixels as acceptable on a standard QVGA 2.5" PDA screen.  It's hard to find an explicit policy on the web for what each manufacturer believes constitutes an acceptable amount of dead pixels for a PDA screen, but instead here's a quick rundown of some major manufacturer policies on how many dead pixels it takes to warrant a return on a notebook computer screen   (below numbers are based on a 14.1" screen with XGA resolution that has a total of 2,359,296 red/green/blue sub-pixels)

Manufacturer Policies for Acceptable Dead Pixel Count on a 14.1" XGA Resolution Notebook Computer Screen

* zero-dead pixel policy only valid in South Korea

Below are some links to various manufacturers policies for allowing return of a laptop due to dead pixels, you'll see there is a wide variation, Apple doesn't even have a set number, you basically have to haggle with them to try and win a return if you feel your LCD display has too many dead pixels.  Acer has a formula and breaks up the screen into sections and defines which area's carry more weight in terms of importance -- if there's more than one dead pixel in the center Acer will replace a laptop, but if the pixels are elsewhere then you can suffer from up to 4 dead pixels per million on the screen.

Links to Dead Pixel Policies:

• Apple Dead Pixel Policy
• Dell Dead Pixel Policy:
• HP/Compaq
• IBM Dead Pixel Policy
• Acer Dead Pixel Policy
• Samsung Dead Pixel Policy (zero dead pixel policy only true in South Korea at the moment)
• Nintendo DS Game System Dead Pixel Policy (Nintendo has a zero-dead pixel policy)
• NewEgg.com (NewEgg.com is a retailer, not a manufacturer, replacement or refund for 8 or more Dead Pixels)

How Can You Tell if you Have Dead Pixels?

Sometimes it is quite obvious as to whether you have a dead pixel on your PDA screen, but sometimes it might take a little while for you to notice.  It's best that you run a test on your screen right when you get your PDA to determine if you have dead pixels and then take the further step of deciding whether you want to try and return the PDA if there are an excessive amount of dead pixels.  Download a free application called Dead Pixel Checker to test for dead pixels on a Pocket PC, or LCD Analyzer for dead pixels on your Palm OS device screen.

Bottom Line

Many people are not aware of the fact LCD screens can have dead pixels.  Some people that are not picky won't be bothered by a tiny black or white dot in the corner of their screen, or maybe they won't ever notice it.  Others that are very picky about their screens will go nuts if there's a dot that they always find themselves focusing on and being annoyed by.  The best advice to be given is to investigate up front what the return policy is for a store or manufacturer before you buy a product with an LCD screen, but as stated earlier, you can be fairly sure most manufacturers consider 3 dead pixels "okay".  Some retailers are very generous and will accept a return for a PDA with just one dead pixel, so you might want to try returning a device to the retailer rather than the manufacturer as another option.  If you haggle enough, it's likely you'll win some money back from a manufacturer on your purchase or talk them into a return if you do have an annoying dead pixel.  But, know ahead of time that one dead pixel is generally not considered a major flaw and you'll need to battle to get a return.  Fair or unfair, this is just the state of the industry at the moment.