The principle of liquid crystal display is simply that the liquid crystal placed between two electrodes is energized, the arrangement of liquid crystal molecules in the electrode will change when the electrode is energized, thus changing the light path of transmitted light to achieve the control of the image.
TFT liquid crystal display panels are composed of the surface layer of protective glass, ternary color filter, polarizing plate, FET transistor (thin-film transistor) electrodes deposited on glass substrate, liquid crystal, liquid crystal and liquid crystal, and then the liquid crystal is deposited into a thin film. The TFT LCD panel consists of a surface layer of protective glass, a ternary color filter, a polarizer, a FET transistor (thin film transistor) electrode deposited on the glass substrate, liquid crystals, a *** pass electrode also deposited on the glass substrate, an underlying polarizer, a backlight plate (light guide), and a backlight. Light is transmitted from the bottom layer and controlled by the liquid crystal and the polarizing plate to produce a colorful image with the help of a filter plate.
According to the physical structure of the common liquid crystal display can be divided into the following types: TN, STN, DSTN three liquid crystal belongs to the passive matrix LCD, their principles are basically the same, the difference is only a slight difference in the angle of distortion of the individual liquid crystal molecules, which is DSTN (commonly known as the "pseudo-color") in early Laptop computer monitors and handheld game consoles widely used, but because it must borrow an external light source to develop the image, so it has great application limitations, but these early reflective monochrome or color without backlight design LCD can be made thinner, lighter and more power-saving, if you can be technically innovative these things for handheld computers and game consoles is still very useful. The TFT thin-film transistor type active matrix LCD is the mainstream of today's LCD applications, it has a fast screen response, good contrast, high brightness, large viewing angle, rich colors and other advantages.
We all know that each point of the TFT LCD by the red, green and blue three parts, in general, 15-inch resolution of 1024X768 TFT LCD point spacing of 0.30mm or so. TFT LCD and CRT monitors are different, with a fixed resolution, only in the specified use of the resolution of its picture quality is the best in the other resolution, can be expanded or compressed in a way to expand or compress. In other resolutions, the image can be displayed in an expanded or compressed manner.
In addition, it should be noted that the traditional display due to the use of electron guns to emit electron beams, in hitting the screen will produce a source of radiation, although its existing products have been a great improvement in technology, the radiation damage continues to reduce, but still can not be cured; and liquid crystal displays it is very low radiation. Traditional display screen using phosphor, through the electron beam strikes the phosphor and display images, thus displaying the brightness than the liquid crystal translucent display is much brighter, in the viewing angle than the TFT liquid crystal display is much better. And in terms of display response speed, traditional displays have good response speed due to their technical superiority.
How to determine the backlight damage
LCD itself does not emit light, its image appearance and brightness adjustment are dependent on the backlight brightness adjustment. In the LCD monitor work, the backlight issued by the light through the LCD screen, the LCD screen display image content into the human eye, then we can see the LCD display text and images. If the backlight is damaged, there is no light emitted, then we can not see anything. However, if we look closely at the LCD screen, we will see a faint image display on the LCD screen, which also indicates that the backlight-related circuit is bad. If the backlight circuit is intact, and the display circuit part of the problem, then we will see the LCD screen behind a bright white light emitted. Most LCD failures are backlight circuit problems or power supply problems, backlight circuit failures in the most likely is the boost coil internal short circuit or broken.
First for the LCD monitor alone to power up, observe the fault phenomenon, whether there is the above fault performance. And then with the host connected to the signal line, open the monitor, observe the monitor power indicator is always green, LCD screen there is no image display (although the backlight is damaged, but through careful identification, you will find that there is a faint image of the display).
Why does the LCD screen appear color spot it
There are two possibilities for color spot, one is the LCD screen localized heavy pressure, the formation of a large area of bad spots. The other is to drive the screen line contact is poor.
What is a high voltage board?
High-voltage power supply board is responsible for the LCD lamp power supply, it will DC low-voltage power supply into a high-frequency high-voltage power supply in order to light up the lamp, belong to the power conversion device, easy to heat, so it is relatively easy to bad. The screen is often dark and the high voltage board is bad!
In fact, the high-voltage board is a switching power supply, only relative to the ordinary switching power supply, it is less rectifier filtering part of the back stage, and focus on high-frequency high-voltage conversion. It will be on the motherboard of the low-voltage DC (generally 3 ~ 14V) through the switching chopper into a high-frequency alternating current, and then through the high-frequency transformer boost, in order to achieve the voltage to light the lamp. High-voltage board power supply and signals from the motherboard, there are generally so many wires connected to the motherboard: power supply V +, power ground G, switch signal S, brightness signal F (some do not have). When the computer is turned on, the power supply, the switching signal S to start the switching oscillator circuit, the switching tube to work, the transformer for the voltage boost, light up the lamp. High-voltage board on the perishable devices are mainly oscillation circuit components, switching tube, high-voltage package.
LCD monitor interface classification standards
Theoretically, because the LCD monitor is a purely digital device, the digital interface is bound to replace the analog interface, but most of the LCD monitors on the market are still using the analog signal interface, the root cause is the specification and standards are not uniform.
At present, the technical standards for digital interfaces are gradually being unified, with more and more display chips having the ability to support digital video output, and graphics card manufacturers starting to integrate digital display interfaces into their graphics cards. Here we introduce three video digital interface standards one by one.
① P&D
The Digital Plug-and-Display (P&D) standard was developed by the Video Electronics Standards Association (VESA), but at the time of its release in 1997, it was already very much out of sync with the reality of the time. For example, the display signal interface defined in the P& D standard, is a multi-functional interface, able to transmit both digital and analog signals, but this point is meaningless, additional USB and IEEE 1394 interfaces in addition to greatly increase the cost, but also for the transmission of display signals is adding to the snake, there is no display card manufacturers are willing to add their own products on such an expensive and useless interface. No graphics card manufacturer wants to add such expensive and useless interfaces to their products. Because of VESA's delay in getting a decent standard, many companies have joined forces with their partners to introduce their own standards, making the current state of digital interface standards confusing.
② DFP
DFP-Digital Flat Panel Group standard is an industry standard proposed by Compaq, the 20-pin DFP interface can support up to 1280X1024 resolution.
The DFP standard was also supported by ATL, a Canadian company that produced the first graphics card with a DFP interface. Later, VESA also selected the DFP interface as a transition to the P&D standard. In fact, if you compare the functional definitions of the two interface standards, you will find that there is no major difference between the two. In the definition of electrical performance, the two is to keep all the same, DFP standard to remove the original P & amp; D interface standard in those expensive and impractical options, such as USB, IEEE 1394, etc., so the DFP standard in the implementation of the time to be much cheaper. However, the DFP standard only supports resolutions up to 1280x1024, and the inherent flaws of insufficient resolution make the DFP interface unlikely to last very long
.