Although the term 'dead pixels' is commonly used to cover all types of pixel fault, there are actually three distinct subcategories: stuck pixels, hot pixels and dead pixels. To understand why dead pixels occur, it helps to know how an LCD monitor works.

In order to generate all the colours of the spectrum, each pixel is made up of three subpixels – one each for red, green and blue light. When all three subpixels are on, the pixel is white, and when all three are off , the pixel is black.

If one or two of these subpixels remain on, the pixel will appear as a solid red, green, blue, cyan, magenta or yellow dot on the screen (depending on which subpixels aren't working). This type of pixel fault is called a stuck pixel.

When all three subpixels are stuck on, the pixel will appear to be permanently white. This type of pixel is known as a hot pixel.

Dead pixels are either whole pixels or subpixels that do not turn on. These pixels always look black. When LCD panels first started to become popular, stuck and dead pixels were quite common and would often appear in clusters.

Too many faulty pixels can render a monitor worthless, so the ISO 13406-2 standard was created to define the maximum number of faulty pixels that are permitted for any given class of display. A Class One panel can't have any faulty pixels, but a Class Four panel can have up to 50 permanently white pixels.

Fixing stuck pixles

Stuck pixels are usually caused by manufacturing defects, and they will often stay illuminated for the life of the panel. In many cases it's possible to fix the pixel using either software tools or manual manipulation.

The software solution will generally flash a series of images that vary in colour and intensity onto the screen in an effort to unstick the pixel.

Manual manipulation involves gently pressing on the affected area with something like a pencil eraser. Doing this compresses the layers of the panel, forcing the oil within the panel to move.

Be careful, though: this is by no means guaranteed to work, and it could create even more stuck pixels or move the problem to elsewhere on the screen rather than repairing it.

Dead pixels and hot pixels are generally the result of faults in the circuitry of the panel. It's usually the case here that the transistor does not switch states properly.

Dead pixels generally mean that the transistor has failed completely, and this is rarely fixable.

Hot pixels may be due to manufacturing defects. They can often be fixed in the same way as stuck pixels, but again, success is not guaranteed.

More help

If you have stuck or dead pixels, we recommend that you try a software solution and only press on the screen as a last resort, as you could end up damaging the panel further. UDPixel is a program that tries to find and fix faulty pixels, as does JScreenFix.

If your screen is new and seems to have an excessive number of faulty pixels for its class, you should contact the manufacturer for a replacement instead.

Three ways to try to fix a stuck pixel

1. The pixel method

UDPixel will attempt to detect and fix problematic pixels for you by changing the screen colour to highlight any problems. Once a fault has been found, you can choose the size of the square and the flash speed to start the fixing process.

2. The browser method

Browser

JScreenFix runs in a browser window and requires the Java Runtime environment. Go to the JScreenFix site, start the applet and then press [F11] to maximise for full screen. You should leave the application to run for an hour or so before viewing the results.

3. The last resort rubber method

In some cases, stuck subpixels can be fixed by gently pressing on the affected area using something that won't damage the panel, such as the tip of a pencil eraser. You should proceed with caution, however. NOTE: this method isn't guaranteed to work, and can make things worse.

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First published in PC Plus Issue 281

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