The flat-panel TV market is heating up day by day, allowing LCD TVs to enter more and more families. However, most users do not understand the principles of LCD TVs. During use, they gradually find that there are always some small dots on the screen that cannot be erased. Although they have no effect on the overall picture, they are always uncomfortable with such defects. The correct term for LCD TV defects is called "bad spots", also known as "dot defects" or "bad spots". It is an irreparable physical damage to the LCD panel, mainly due to the corresponding parts of the bad spots Caused by local damage.
Talking about the formation of dead pixels from the principle
The core of the LCD TV-the LCD panel is composed of countless pixels, which is also the smallest unit for the LCD TV to display images, and after the countless pixels form an array, the amount of dots and surface changes, forming a picture For complete images, most display devices are constructed based on this principle. The dead pixels are the irreparable pixels on the LCD panel, which are generated in the production process in most cases.
Each pixel of the liquid crystal panel corresponds to three relatively independent liquid crystal cell boxes. Compared with CRT and plasma, each pixel point corresponds to a phosphor box. The structure is more complicated. The liquid crystal panel is composed of fixed liquid crystal pixels. Each liquid crystal cell is equipped with a strip of liquid crystal material. The voltage can be changed by a corresponding driving tube to change the optical rotation state of the liquid crystal to obtain unused light flux. The box can be seen as a tiny light valve. Red (R), green (G), and blue (B) filters are added to the front of the liquid crystal cell, and the illumination of the last tube and the refraction of the front glass can make the pixels change differently according to the needs. colour. This is the most basic LCD panel imaging principle, and any LCD TV is developed on this basis.
From here we can see that this method requires a lot of liquid crystal cell boxes to compose. Taking a 32-inch LCD TV with a resolution of 1366 & TImes; 768 as an example, the calculation method of the required liquid crystal cell box is 1366 & TImes; 768 & TImes; 3, which is 3,147,264 This! This requires the same number of drive tubes to apply voltage to drive them. This is bound to pose a high challenge to the existing manufacturing technology. During production, any failure of any drive tube will directly cause the liquid crystal material to fail to rotate, thus causing the generation of dead spots. The dead pixels cannot be changed according to the instructions of the circuit, but are always displayed as a color. If one or more of the three primary colors of red, green and blue are faulty, the pixel cannot change the color normally and will become a fixed color point, which can be clearly seen under certain background colors, which is bad point. The bad spot is a physical damage that cannot be avoided 100% in the production and use of the LCD screen. In most cases, it is caused by the screen manufacturing. Impact or natural loss during use may also cause a bad spot. As long as one or more of the three primary colors that make up a single pixel are damaged, dead spots will occur, and both production and use may cause damage.
In-depth reading of the classification of dead pixels and panels
Depending on the degree of damage, dead pixels can be divided into two categories:
The cause of this situation is that the three LCD cell drive tubes corresponding to the pixel point have failed. When switching to the red, green, and blue display, these three cell boxes are always parallel or perpendicular to the LCD panel. Position, resulting in pixels that always appear as pure black or pure white in any color.
Highlights: The reason for this situation is that one or two of the drive tubes of a liquid crystal cell corresponding to the pixel point have failed. When switching the red, green, and blue display, these cell boxes are always in contact with the liquid crystal panel. Vertical position. The pixels of one of the red, green, and blue colors that appear when the screen is black; or when one of the three colors of red, green, and blue should be presented, it can only show white, while in the other two In the mode, there are other non-natural color points. The former case can be determined as one drive tube damaged, and the latter case can be determined as two drive tubes damaged.
Dark spot: The reason for this situation is the opposite of the bright spot. One or two cell boxes damaged when switching the red, green, and blue display are always parallel to the liquid crystal panel. Pixels other than pure red, green, and blue appear in the case of a white screen. According to the display of the three colors of red, green and blue at the same position, it can be determined in the dark point how many LCD driver tubes are damaged. Of the three colors, two colors can be correctly displayed. When the additional one is displayed as black, it can be determined that one drive tube is damaged. Only one color can be correctly displayed among the three colors, and the situation when the additional two colors are displayed as black can be determined as the damage of the two driving tubes.
Unfortunately, with the current technology and process, there is no guarantee that every batch of LCD screens produced will have no bad spots, and only the method of avoiding the bad spots can be used to cut the LCD panel. According to the number of bad points, the flatness of the LCD panel is distinguished. The standard for the bad points of the LCD panel established by the ISO organization is: Class 1 does not allow dead points; Class 2 allows 3 dead points; Class 3 allows 3 More than 10 dead pixels; Class 4 allows more than 10 dead pixels.
However, panel manufacturers do not distinguish strictly in accordance with ISO standards, but are divided into A +, A, B, C and other models. The nominal of Japanese panel makers is A level within 3 dead pixels, South Korea with A level within 5 and Taiwan standard with A level within 8 points. Of course, this changes according to the continuous improvement of the production process, not static, which must be paid attention to before purchasing. In addition, due to the different standards for the definition of dead pixels in different parts of the world, due to the insufficient cost of liquid crystal panel technology and manufacturing processes, many manufacturers in the industry currently assume that the dead pixels of a panel are less than 3 to 6 If it is a qualified product, only some products that use the A + panel will make a promise of zero bright points or zero dead points.
Flat panel TVs are one of the products with a relatively high complaint rate on the market. Various manufacturers have different attitudes towards dead pixels and maintenance issues, so the problem of dead pixels in the market is still confusing. Some brands have no bright spots, the main reason is that the bright spots have a relatively small impact on the picture, and manufacturers use some technical means to convert the bright spots into dark spots. It is more common to stipulate the number of dark spots, that is to say, how many dark spots are on the screen is normal and cannot be replaced. For consumers, although the effect of dark spots on the picture is not very obvious, but it can be found by careful observation, and most consumers will not spend a high price to buy a product with defects.
The main reason for this situation is that in the after-sales maintenance of LCD TVs, the repair price of the LCD screen is relatively high. After such a problem occurs, like the general maintenance outlets, there is no way to solve it. To return to the factory to replace the LCD screen, and the price of the LCD screen accounts for more than 70% of the price of the LCD TV, so it will inevitably increase the cost, so most manufacturers It's no surprise that LCD screens have such an attitude with regard to dead pixels.
Therefore, from the author's point of view, the choice of LCD TV must solve these problems before payment. Rather, it takes a little more time to choose an LCD TV without any defects, and do not make a decision in a hurry. The decision before payment is in your hands, you have the right to decide whether to buy this TV, and after payment, basically only at the mercy of the manufacturer.
For users who have problems, most color TV brands promise free home repairs during the warranty period, but the price charged outside the warranty period is relatively high. However, if you want to exchange products, according to past experience, it is generally possible to be satisfied only when the bad points are more serious. The reason has been mentioned earlier that the cost of the manufacturer is too high. For warranty, the current "Three Guarantees" regulations only apply to black-and-white TVs and color TVs. The "Three Guarantees" regulations also do not clearly define the maintenance of flat-panel TV products including LCD TVs, resulting in various The big players are on their own. In terms of the LCD TV warranty regulations of major domestic manufacturers: Xia Xin is a one-year warranty for the whole machine; TCL is a one-year warranty for the whole machine and main components; Changhong has a different warranty period for each model; Sharp is a 1-year warranty; Xia Hua It is 1 year for the whole machine and 3 years for the main parts.
In April of this year, the Ministry of Information Industry promulgated the standard “General Specification for Digital TV LCD Display†No. SJ / T 11343-2006, which has certain reference for consumers. Among them, it is stipulated that: LCD TV area A is not allowed There are any white or green bright spots, and one red or blue bright spot is allowed; the whole screen is allowed to have two bright spots, but 2 is not allowed in any area of ​​1/9 screen height and 1/9 screen width on the screen More than one white or green bright spot, that is to say, if the distance between two white or green bright spots is too close, it is also a failed screen. Area A refers to the area where the center width of the screen is the same as the height of the screen, and the area other than Area A is Area B. This standard is what we usually refer to as the national LCD industry standard, but this standard will not be implemented until January 1, 2007, and is only a recommended standard, not mandatory. However, LCD national industry standards can be used as a standard and reference for consumers to buy LCD TVs.
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