See the figure below an example of a type of LCD monitor, 15 inches:

The LCD monitors have many advantages over the conventional, such as:

- They are thinner and lighter. For that occupy less space on the table;

- No heat as the conventional;

- Consume less power;

- Do not tire your eyes;

- The entire floor area of the screen is occupied;

- Never get the picture blurred.

But they have some disadvantages compared with the traditional, such as the possibility of the LCD screen has some "dead pixel" which is a white or black in the area of the screen or to the fact that the brightness and contrast is less than the conventional screen. But with new techniques for the manufacture of LCDs is they can compete with the tubes in terms of brightness and contrast.

TFT LCDs TYPE USED IN MONITOR and TVs
The LCD screen is the equivalent of the tube image of traditional monitors. It is composed of several layers and below we have all the diffuser of light, which is a white plastic plate that distributes the light of two or more cold cathode fluorescent lamps in (CCFL) uniformly behind the screen.

Also within the module to find the LCD display driver ICs of the pixels that form the images in this display. In the picture below we have a picture taken from a display of a monitor showing in detail the terminals of one of CCFL lamps:

Important: The display of LCD module is a single, so any defect which he were to, such as spots, dead pixel, broken glass, CI or lamp burned, he should be replaced whole, as happened with the conventional tube monitors when they weakened, burned or hinder the filament in short.

HOW THE LIQUID CRYSTAL controlling light
Liquid crystal - It is a substance with the characteristics of the solids and liquids. With solid the molecules are close and well organized in structures. Already in the liquid molecules are much more separate and move in different directions. In the liquid crystal molecules are arranged in structures, but not as close as in solids. See below:

When a light beam passes through the molecules of liquid crystal, its direction is changed. So just put the plate liquid crystal between two polarizing, apply tension between them and make the light pass through one of polarizing, through the liquid crystal to reach the other polarizer.

Polarizer - filter glass formed by grooves that only lets the light pass in a direction. The polarizadores are placed at the ends of the liquid crystal with the grooves to a 90 for the other. Among them is a source of tension that can be turned on or off. See the structure in the picture below:

When no voltage applied between the polarizing, the light passes through the first and the molecules of liquid crystal rooting in 90 of the light so that it can cross the second and becomes visible in front of the display. Thus the display is clear. When there is tension between the applied polarizing, the molecules are oriented in another way so as not to change the direction of the light from the polarizer 1. Thus the light can not leave the polarizer 2 and can not be seen in front of the display. Thus the display is dark. Controlling the level of voltage applied between the polarized and can vary the level of light that pass through the display.

A DIVISION OF LCD DISPLAY AND TFTS

Pixel - It is the smaller part so that the image. Each pixel is composed of 3 sub, a red (R), another green (G) and other blue (B). The LCD screen is divided into pixels and subpixels. For example: SVGA screen has a resolution of 800 columns x 600 lines. Hence it is composed of 480,000 pixels. Since each pixel has 3 colors, then gives a total of 1,440,000 rooms this screen. Already has a screen XVGA resolution of 1024 x 768, has 2,359,296 pixels and 786,432 rooms. The higher the screen resolution, it should have more rooms. Each division (sub) of the screen is controlled by a tiny transistor MOSFET mounted on a glass block located behind the liquid crystal. Each transistor that is called TFT.

TFT - "Thin Film Transistor" - or thin film transistor, a transistor is mounted on a glass substrate. As explained, the LCD monitor has millions of transistors on a glass TFT MOSFETs located between the polarizer 1 and the block of liquid crystal. An LCD screen resolution of 800 x 600 owns 1,440,000 of these transistors mounted on the glass. Each transistor is responsible for doing its sub let the light (on) or block (off). Below is the basic structure:

Each transistor TFT is driven by gate line and the line of digital pulses through source-level "0" or level "1". When the gate and source receive Level 1 (tension), the TFT leads and let the light pass through the sub, it appears green, red or blue clear in front of the screen. When the gate or the source receive level 0 (no tension), the TFT leads and sub is not erased. For each image formed on the LCD panel, TFT each received eight bits "0" and "1" at a time. If all bits are 1, sub shows that the maximum brightness. If all the bits that are 0 sub is erased. If some bits are 0 and others are 1, the sub lights up and erase eight times and fast so that our eyes see a bright weaker.

As each sub (color) receives 8 bits at a time, he can make 256 levels of brightness. Since each pixel has three colors, multiplying the 256 levels of brightness for each one, it appears that this pixel can play 256 (R) x 256 (W) x 256 (B) = 16,777,216 colors, ie more than 16 million Color.

The capacitors' storage 'store for a few moments of brilliance that the information sub.
The TFT LCDs using transistors are called active matrix and provide greater vibrancy to the image, being used by all computer monitors and LCD TVs of today.

CONTROL OF THE Transistor TFT LCD DISPLAY
The connection between the LCD display board and the monitor is made by a connector called LVDS (low voltage differential signaling). Once the digital data are applied to the display by lines of 0 to 1.2 V providing higher speed of data transfer and without noise. When passing by LVDS connector, the data goes to a driver IC and the display of multiple ICs for ILD providing the bits of transistors to drive TFT. The IC controller of the display is located on a plate attached to the glass substrate where are the TFTS. But the ILD ICs are between the plate and glass substrate. But these components are not replaced when they burn. The solution is the return of the entire display. See the figure below the location of ICs to drive the transistors of the TFT display:

On board display also enter a B + of 3.3 or 5 V to feed the ICs to control and ILD.

STRUCTURE OF DISPLAY AND LCD backlight ( "BACKLIGHT")

As explained, the LCD display is a sandwich of plates and glass substrates, and the structure of the backlight ( "backlight"). See below:

LCD screen - It is made up of the following components:
Polarizadores - Just let the light pass in a direction;
Plate TFT - Substrate glass where are the MOSFETs transistors that control the brightness for each individual sub;
Color filter - glass substrate that gives the colors to RGB subpixels controlled by MOSFETs;
Liquid crystal - Modifies or not the path of light passing through it depending on the voltage applied between polarizadores MOSFETs by the TFT plate.

Backlight - It is formed by:

CCFL lamps - cold cathode fluorescent lamps for use to illuminate the display. The monitor can have two or more of these;
Source inverter - Or turn provides between 300 and 1300 VAC to feed the bulbs. By controlling the voltage for the lamp, adjust the brightness of the display;
Guide to light - Drives the light for the LCD display;
Shooting - the reflection light to the guide;
Diffuser - Spread the light uniformly by Backlight unit;
Prisma - Transfer the light from the backlight unit for LCD display.

Circuit board of the LCD display - Contains the CI of the display controller ICs and the ILD to provide the bits of trigger for the TFT. The screen LCD, the backlight unit and printed circuit board form a single whole and as I explained, defect if it anywhere, the whole thing should be replaced.

LAMPS IN THE LIGHT OF LCD DISPLAY

As explained the lighting is made with cold cathode fluorescent lamps in (CCFL). These lamps have a glass tube containing inert gases inside (neon, argon and mercury), two domestic terminals called cathodes and a layer of phosphorus in the internal walls of glass. Applying a high voltage between the cathodes, the domestic gas and emit light if ioniza ultraviolet (UV). The UV excites the phosphorus from within which then produces visible light the lamp in the tube. For greater durability of the lamp she must work with alternating voltage. If it also turns on continuous tension, but over time the gases accumulate in corners of the lamp, the dark-and light producing an uneven in these regions for the rest. Here's the layout of CCFL lamps powered by alternating tension and continuing:

The CCFL lamps are powered by alternating voltage of 300 to 1300 V. This tension is obtained from a source reverse. This source is made up of transformers, transistors and chaveadores IC oscillator that works on high frequency (between 40 and 80 kHz). The reverse turns then a continuous low voltage between 12 and 19 V for a high-voltage alternating light bulbs. The source is reversed and easy to find on the monitor. Just follow the wires of the lamps (two cables to each). The plate where they are embedded is the reverse. Below is the location of the source of a reverse LCD monitor:

In reversing source also enter a sign of coming from plaque control of the monitor to control the voltage supplied to the lamps and thus adjust the brightness of the screen. Also control enters a signal to turn off the lamp in case of any failure in the system such as the burning of one of the lamps of the display.