February 23, 2017 | Author: Gerardo Rubin | Category: N/A
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Preface You may distribute this ebook freely. The ebook is illustrated with 40 colorful photos of LCD Monitors. It explains the basic functions, major components and repair guide of LCD Monitor which is required to be fully understood and will be a knowledge channel of being a succesful LCD Monitor repairer.
Friendly Reminder The reader is expressly reminded to consider and adopt all safety precaution that might be indicated by the activities herein and to avoid all potential hazards. Although all possible measures have been taken to ensure
the
accuracy
of
the
information
presented,
neither
Lcdmonitorrepairebook, nor the author are liable for damages or injuries, misinterpretation of directions, of the misapplications of informaiton. By following the instructions contained herein, the reader willingly assumes all risks in connection with such instructions.
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CONTENT
1. INTRODUCTION: LIQUID CRYSTAL DISPLAY MONITOR 2. HOW THE LIQUID CRYSTAL LIGHT CONTROL 3. DIVISION OF LCD DISPLAY AND TFTS 4. BASIC STRUCTURE OF TFT LCD DISPLAY 5. CONTROL OF TFT LCD DISPLAY TRANSISTORS 6. STRUCTURE OF THE LCD DISPLAY AND BACKLIGHTING 7. BACKLIGHTING OF THE LCD LAMPS 8. HOW TO OPEN THE LCD MONITORS 9. INTERNAL BOARDS OF LCD MONITOR 10.BLOCK DIAGRAM IN LCD MONITOR 11.IDENTIFICATION OF MAJOR COMPONENTS IN MAIN BOARD 12.IDENTIFICATION OF MAJOR COMPONENTS IN POWER SUPPLY BOARD 13.IDENTIFICATION OF MAJOR COMPONENTS IN POWER INVERTER 14.PROCEDURE FOR LCD MONITORS REPAIR 15.DEFECTS IN LCD DISPLAY 16.OTHER DEFECTS IN STEPS OF MONITOR 17.EXAMPLE OF IC REPLACEMENT IN LCD MONITOR 18.PROCEDURE FOR IC REPLACEMENT IN LCD MONITOR 19.COMBINATION OF SCALAR AND MICRO IN ONE IC
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LIQUID CRYSTAL DISPLAY MONITOR
The LCD screen is the equivalent of the picture tube monitors. It consists of several layers and below all have the light diffuser, which is a white plastic plate that distributes the light from two or more cold cathode fluorescent lamps (CCFL) uniformly behind the screen. Also within the module of display drivers find the ICs of the pixels that form images on this display. In the figure below we have a picture of one taken from a display monitor showing in detail the terminals of the CCFL lamps:
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Important: The LCD display is only one module, so any defect which comes to present, including blemishes, dead pixel, broken glass, light bulb or IC, it should be swapped round, as well as with the conventional tube monitors when they are weakened, the filament burned or going short.
HOW THE LIQUID CRYSTAL LIGHT CONTROL:-
Liquid crystal is a substance with characteristics between solids and liquids. In solids the molecules are close together and organized structures. Already in the liquid the molecules are far apart and move in different directions. In the liquid crystal molecules are arranged in structures, but not so close as in solids. See below:
When a light beam passing through the liquid crystal molecules, its direction is changed. Then just put the plate of liquid crystal between two polarizers, apply tension between them and make the light go through one of the polarizers, through the liquid crystal to reach the other polarizer.
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Polarizing Filter - glass formed by grooves that only lets the light pass in one direction. The polarizers are placed at the ends of the liquid crystal with the slots at 90 degrees relative to each other. Among them will a source of tension that can be turned on or off. See the structure in the figure below:
When no voltage is applied between the polarizers, the light passes through the first and the liquid crystal molecules twist light by 90 ° so that it can cut through the second and becomes visible in front of the display. So the display is clear. When voltage is applied between the polarizers, the molecules are oriented differently so as not to change the direction of light from a polarizer. Thus the light can not leave the polarizer 2 and can not be seen in front of the display. So the display goes dark. Controlling the level of voltage applied between the polarizers is possible to vary the level of light that pass through the display.
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DIVISION OF LCD DISPLAY AND TFTs
Pixel - is the smallest part that forms the image. Each pixel comprises three subpixels, one red (R), one green (G) and one blue (B). The LCD screen is divided into pixels and subpixels. For example, an SVGA screen has a resolution of 800 columns x 600 rows. Hence it is composed of 480,000 pixels. Since each pixel has three colors, gives then a total of 1.44 million rooms in this screen. Already have an XVGA screen resolution of 1024 x 768, has 786,432 pixels and 2,359,296 divisions. The higher the screen resolution, more divisions it should have. Each division (sub-pixel) screen is controlled by a tiny transistor mosfet mounted on a glass block located behind the LCD. Each of the transistor is called TFT.
TFT - Thin Film Transistor "- or thin film transistor is a transistor mounted on a glass substrate. As explained, the LCD monitor has millions of transistors on a glass TFT mosfets located between the polarizer and a liquid crystal block. An LCD screen resolution of 800 x 600 has 1.44 million of these transistors mounted on the glass. Each transistor is responsible for making their subpixel pass the light (on) or block (off). Below is the basic structure shown in the next page:
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BASIC STRUCTURE OF TFT LCD DISPLAY
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BASIC STRUCTURE OF TFT LCD DISPLAY
Each transistor is driven by the TFT gate line and the line of source pulses through digital level "0" level or "1". When the gate-source and receiving a level (voltage), the TFT is driving and lets light pass through the subpixel, this appearing green, red or blue and clear in front of the screen. When the gate or the source receive level 0 (no tension), the TFT is not conducive and the subpixel is off. For each image formed on the LCD panel, TFT each receives eight bits "0" and "1" each time. If all bits are 1, one subpixel has the maximum brightness. If all bits are 0 subpixel that is off. If some bits are 0 and others are 1, the subpixel is eight times turns on and off very
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quickly so that our eye sees brightness weaker.
Since each subpixel (color) receives 8 bits at a time, he may have 256 levels of brightness. Since each pixel has three colors, multiplying the 256 brightness levels for each one, it follows that this can reproduce 256 pixels (R) x 256 (G) x 256 (B) = 16,777,216 colors, or more than 16 million colors.
The capacitors “storage” to store a few moments of briliance that subpixel information. LCDs are called using transistors TFT active matrix and provide greater vibrancy to the image being used by all computer monitors today.
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CONTROL OF TFT LCD DISPLAY TRANSISTORS
The connection between the LCD and the board of the monitor is made by a connector called LVDS (low voltage differential signaling). Thus the digital data are applied to the display by lines of 0 or 1.2 V providing higher speed transfer of data and no noise. By going through the LVDS connector, the data goes to a driver IC and the display of ICs for various LDI providing the bits to drive the TFT transistors. The display driver IC is located on a plate attached to the glass substrate where are the TFTs. The display driver ICs are connected LDI between the plate and glass substrate. But these components are not replaced when they burn. The solution is to exchange the entire display. See the figure below the location of transistor TFT display driver ICs:
On board display also enter a B + 3.3 or 5 V to power the control IC and LDI.
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STRUCTURE OF THE LCD DISPLAY AND BACK LIGHTING
As explained, the LCD is a sandwich of plates and glass substrates, as well as the structure of the backlight. See below:
LCD screen is comprised of the following components: Polarizers - Just let the light pass in one direction; Plate TFT - glass substrate where are the mosfets transistors that control the brightness for each individual subpixel; Color filter - glass substrate that gives color to the RGB subpixels controlled by mosfets; Liquid crystal - Modifies or not the path of light passing through it depending on the voltage applied between the polarizing plate by mosfets TFT.
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Backlight is formed by:
Lamps CCFL - cold cathode fluorescent lamps used to illuminate the display. The monitor can have two or more of these; Power inverter - provides between 300 and 1300 VAC to feed the bulbs. By controlling the voltage to the lamp, adjust the brightness of the display; Light guide - Directs light to the LCD display; Spotlight - Reflect light to the guide; Diffuser - spreads the light evenly in the backlight unit; Prisma - Transfer the drive light to backlight the LCD display.
Printed circuit board to the LCD display - Contains the display driver IC and IC to provide the LDI bit to drive the TFT. The LCD screen, the backlight unit and printed circuit board form a just and as already explained, with defect in any part of the whole thing must be replaced.
BACKLIGHTING OF THE LCD LAMPS As explained the lighting is done with cold cathode fluorescent lamps (CCFL). These lamps have a glass tube containing inert gas inside (neon, argon and mercury), two domestic terminals called cathode and a layer of phosphor on the inside walls of glass. Applying a high voltage between cathodes, the internal gas is ionized and emits ultraviolet (UV). The UV excites the phosphor into visible light which then produces the tube lamp. For prolonging bulb life it should work with AC voltage. If it also turns on voltage, but with time the gases accumulate in the corners of the lamp, darkening them and producing an uneven light in these regions relative to the rest. See diagram these CCFL lamps fed with AC voltage and continuous
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The CCFL lamps are fed with alternating voltage 300-1300 V which is obtained by a power inverter. This inverter consists of transformers, switching transistors and oscillator IC working at high frequency (between 40 and 80 kHz). The inverter then becomes a voltage low between 12 and 19 V on a high alternating voltage to light the lamps. The power inverter is very easy to find on the monitor. Just follow the wires of the lamps (two cables for each). The board where they are embedded is the power inverter. Below is the location of the power inverter of an LCD monitor:
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In the power inverter also enter a control signal coming from the board of the monitor to control the voltage supplied to the lamps and thereby adjust the screen brightness. Also enter a control signal to turn off the lamp in case of fault in the system such as the burning of the lamps of the display.
HOW TO OPEN THE LCD MONITORS Most LCD monitors have locks on the cover of which should be released for opening the housing. We take great care not to break these locks and / or knead the monitor case to try to unlock using screwdrivers or other metal objects. After removing the screws the lid open a crack between the lid and the front of the monitor. Enter this hole a piece of card or wood phenolite. Drag wood or phenolite forcing the crack slightly regions where the locks are going until they drop. After just remove the cover. Below is a sequence of disassembly of an LCD monitor "Samsung" shown in the next page:
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For special opening technique, click this ebook photo for detail, or access to the following web site http://www.lcdmonitorrepairebook.com/lcdmonitorrepair.htm
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INTERNAL BOARDS OF LCD MONITOR By opening a monitor this board find a motherboard on the LCD. We also find a label attached to lamps of the display. This is the power inverter board. There are cases where the inverter is on the board to alternate the power supply voltage monitor. We will also have the card on the main keyboard connected via a connector. Some monitors will find a board where it enters the AC cord. This is the power supply board. Below is an LCD display showing dismantling their boards:
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BLOCK DIAGRAM IN LCD MONITOR In the diagram below we see how to divide the block of LCD monitors and then have the function of its circuits:
DB15 - This is the same as conventional monitor. Carries the RGB signals and synchronization to the monitor. Pins 1,2 and 3 receive the signals coming from the analog RGB video card from the computer and send them to the scalar IC. 13:14 The pins receive the synchronization signals and send them along with the micro communication DDC (display data channel) coming from pins 12 and 15. The function of the DDC is to make the computer recognize your monitor model and install any drive for better
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performance.
DVI connector - This is optional and carries the video signal has already scanned the computer monitor. Recalling that the LCD monitor is digital, unlike conventional analog that is. Thus the reproduced image has higher quality than that imposed by the DB15 connector. The disadvantage is that the DB15 video card in the computer must convert the digital signal to analog and the monitor switch from analog to digital again. In this process there are losses in the video signal, which does not happen when using the DVI connection between the computer and LCD monitor.
Scalar IC - The largest and main SMD IC LCD monitor. It receives the RGB signals coming from the DB15 connector or the DVI digital video and converts them into digital signals suitable for the production of images on the LCD. The scalar provides signals corresponding to 60-75 complete frames per second for the LCD display. The signals are transferred to the display with an LVDS connector. Inside the scalar is going SDRAM storing the images processed by the complete IC. Hence the IC reads each image and release this data quickly to the LCD display. This IC also converts the analog RGB signals into digital DB15 connector and makes the contrast control and other necessary corrections to the image before sending them to the display. The IC is controlled by micro scalar. A flaw in scalar lets the monitor with the screen lit but no picture.
LVDS - "Low voltage differential signalizing" traffic or low voltage differential signals - is a connector with means of 0 or 1.2 V that transfers digital signals from the scalar of the display at high speed and with minimal noise.
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Micro IC (or MICOM) - Go on the keyboard and the monitor controls functions such as brightness, contrast, etc. It is a SMD IC and goes on the scalar to control the contrast and the rate of transfer of images per second for the display (resolution). The microcomputer is also connected at the power inverter to connect, disconnect and control the brightness of the display lamps. On some monitors the computer is with the scalar in a single IC. The EEPROM stores the data display control.
Clock - a clock signal is produced from a quartz crystal. It is necessary to synchronize the data transfer between digital ICs. Without the digital clock ICs do not work.
LCD display - Converts signals from the scalar in images. As seen the display receives a complete picture at a time scalar. Are 60-75 frames per second depending on the rate chosen under Windows. In the display module for the IC and control ICs that trigger the LDI transistors TFT.
Power Inverter - Transforms + B between 12 and 19 V in voltage alternating between 300 and 1300 V for lighting lamps CCFL display. It is controlled by computer.
Power supply - Transforms the alternating voltage network (110 or 220 V) continuous power in the operation of the monitor. Usually provides a B + 5 V for the LCD and the motherboard which will then be covered in 3.3 and / or 1.7 V to power the scalar and the micro, and another B + between 12 and 19 V feed the inverter board.
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IDENTIFICATION OF MAJOR COMPONENTS IN MAIN BOARD In the photo below we have the motherboard on a Samsung monitor highlighting its main parts:
First find the two largest SMD ICs. The biggest is the Scalar and the smallest is the Micro. Even the latter is near the keyboard connector and the IC has EEPROM of eight terminals on the side. Near the Scalar have the crystal clock. On one side we have the Scalar DB15 connector that carries the signals to the monitor and the other end are the outputs for LVDS LCD display. Near the source we have the connector IC voltage regulators and their electrolytic filter. The regulators provide B + 3.3 and 2.5 V to power
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the scalar, micro and LCD display.
Mosfet IC - It's a switcher mosfet regulator or mounted inside an IC containing various terminal source and drain terminal and a gate to control. In that way we get a good heat dissipation in a small space. This component type is common in LCD monitors.
IDENTIFICATION
OF
MAJOR
COMPONENTS
IN
POWER
SUPPLY BOARD In the photo below we have the power supply board on a Samsung monitor highlighting its main parts:
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After the entry of the power cord have a coil and some large capacitors. Are network filters that let the system voltage enter and leave the frequency of the power switch out to not interfere with other devices. The following is the fuse, bridge rectifier and electrolytic main filter. After this we have the power switch formed by the IC oscillator and switching device, the chopper transformer, rectifier diodes and the electrolytic filter the rows of B + which will feed the circuits of the monitor.
IDENTIFICATION
OF
MAJOR
COMPONENTS
IN
POWER
INVERTER In the photo shows in the next page is the circuit of a Samsung monitor at the top and bottom of PCB.
We located a large transformer in the middle of the plate. It provides the AC voltage to power the lamps of the display. We can observe that the connector on both lamps are connected in said transformer. Sometimes there are two transformers, one for each lamp (in the case of the display using two bulbs). The primary of the transformer is going on in two transistors (typically MOSFETs) that turn on and off the winding in the frequency 40-80 kHz. So the transformer transfers a large alternating voltage to the secondary (which has more turns than the primary). This potential difference will light the lamp. The mosfets are controlled by an oscillator IC. The power inverter circuit is controlled by micro motherboard, as well as the oscillation frequency to adjust the brightness of the lamp.
Take care not to touch the welds on this card when it is energized. The shock at high voltage is not fatal, but it hurts a lot.
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PROCEDURE FOR LCD MONITORS REPAIR This is the part that everyone was expecting. The procedures to fix these types of monitors. Before we classify the defects into two groups: those related defects in the display and connected with other circuits, in some cases may also be on display.
DEFECTS IN LCD DISPLAY They are usually failures requiring complete replacement of the display. The LCD Monitor’s failures are caused by one or some transistors TFT burned, or IC lamp burned on the display board or the breaking of glass or spots on the display. See the figure below some defects related to display:
For the stained glass screen solutions, click this ebook photo for detail, or access to the following web site http://www.lcdmonitorrepairebook.com/lcdmonitorrepair.htm
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For the dead pixel solutions, click this ebook photo for detail, or access to the following web site http://www.lcdmonitorrepairebook.com/lcdmonitorrepair.htm
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For the horizontal or vertical bar solutions, click this ebook photo for detail, or access to the following web site http://www.lcdmonitorrepairebook.com/lcdmonitorrepair.htm
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OTHER DEFECTS IN STEPS OF MONITOR In the figure below we have some symptoms of defects in LCD displays.
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For the no led, no signal, dark image or dim solutions, click this ebook photo for detail, or access to the following web site http://www.lcdmonitorrepairebook.com/lcdmonitorrepair.htm
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EXAMPLE OF IC REPLACEMENT IN LCD MONITOR
Below is an example of a fairly common defect in the lines of monitors Samsung 510N, 540N, 710N and 740N. Appears only one square that is passing across the screen indicating lack of signal on the cable (even that attached to the computer) or resolution error. This failure occurs because of an internal program error occurred in micro IC. In this case, the solution is the replacement of the IC and SMD as we take some care in this procedure.
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PROCEDURE FOR IC REPLACEMENT IN LCD MONITOR
REPLACEMENT OF SMD IC We will need the following materials: - Soldering iron 30 W or 40, fine tip and very clean; - Solder joint quality such as "Best" or "Cobix" - Welding of low melting; - Flow weld pitch (+ isopropyl alcohol); - A piece of wire mesh or failing that a stalk pickled; - Isopropyl alcohol to clean the plate; - Brush teeth; - Piece of cotton cloth (old t-shirt kind of mesh).
1 - Purchase a new IC with the exact same code that to be changed, especially for PCs. Parts for LCD monitors can be found at your nearest specialty stores.
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2 - Spread the low-melting solder all pins of the IC that will be replaced. Take care not to exaggerate the amount of soldering. Then using the tip of the soldering iron to solder heat evenly on all pins of the IC. Using a small screwdriver to lever up the IC card so that it falls on the bench. Then remove the remains of the plate with the solder iron tip. On the trails of the board where the IC soldier was cleaning can be done with wire mesh: Spread flow of solder on the tip of the loop, pull it on the trails. Place the tip of the iron in the mesh and the heat this will attract the remains of soldiers who were on the trails. Then clean the rest of the plate with a toothbrush, rubbing alcohol and cloth shirt. See below the IC has desoldered from the board:
3 - Correctly place the new IC on the tracks of the board and apply solder joint on the pin ends of the IC, do not worry about the pins that get shorted. The purpose of this operation is to set the IC on the board.
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4 - Apply a small amount of soldering flux on one side of the IC. Make a big ball of solder on the pins of the tip on this side where it was applied to the stream. Lift the plate and slide the tip of the soldering iron pulling the weld down. The solder will come down, solder the pins on the tracks and because the flow will not be between two pins. If you happen to be two or more pins stuck can unglue them using wire mesh embedded in the stream, flush against the pins stuck, heating and so it attracts the solder unwinding short. See the figure below the IC again already on the board and the monitor back to working order:
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NOTE FINAL The Micro IC LCD monitor also often called MiCOM or MCU and some more modern monitors along with the scalar is a single chip. Below is an example of a chip 100 terminals used by modern LCD monitors from LG and it has the scalar and micro together shown in the next page.
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COMBINATION OF SCALAR AND MICRO IN ONE IC This is example of Single IC of Scalar and Micro’s combination.
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My dear reader,
Here is the end of ebook which covers the basic knowledge of LCD Monitor repair guide.
For further information, you may buy this ebook which reveals much more secrets of LCD Monitor Repair in quick and easy way. Imagine how fast you trouble-shoot the faulty LCD Monitors and receive money from your customer. It is our recommendation to continue upgrade your LCD Monitor repair skill and keep it up. Click this ebook photo for detail, or access to http://www.lcdmonitorrepairebook.com/lcdmonitorrepair.htm
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