Lcd monitor repair guide pdf

 

    TV Repair Tips V LCD TV Repair Tips & Case Histories LCD/LED & 3D TV Recommended Troubleshooting & Repairing Guide: V –LED & LCD TV. This is a copyrighted material; no part of this guide may be reproduced or transmitted in any form whatsoever, electronic, or mechanical, including photocopying. Download LCD MONITOR REPAIR GUIDE service manual & repair info for electronics experts.

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    Lcd Monitor Repair Guide Pdf

    Download LCD MONITOR REPAIR GUIDE JESTINE YONG service manual & repair info for electronics experts. This is a copyrighted material; no part of this guide may be reproduced or transmitted in How to Repair LCD Monitor Power Adapter How to Repair No saicumspecsacont.tk Voltage test. The third. No much lcd monitor repair book or Lcd Monitor Repair Pdf has compiled these questions. 1) how repair lcd monitor with no power problem, 2) how trouble.

    The questions sound like the following. No much lcd monitor repair book or Lcd Monitor Repair Pdf has compiled these questions. For example, when a lcd monitor has no power problem, you will trouble shoot the power supply board directly. Learn your knowledge on studying the lcd monitor schematic, go deeper to the power supply board, you will find the switch mode power supply smps. Due to variations in the main input supply, the dc level will fluctuate widely and feed the unregulated dc directly to the high frequency power switching section which is the central block of the supply.

    For example S3 is a 4.

    SMD Resistors are usually coded with a numerical equivalent of the familiar three band color code. Some examples of SMD Resistors will make this clearer: The letter indicates the working voltage and the 3 digits 2 digits and multiplier give the capacitance in pF.

    The first letter if present is a manufacturer code i. SMD ceramic capacitors are sometimes marked with a code. In the same way as wire ended components. The first two or 3 digits are the first two or 3 digits of the resistance in ohms.

    For SMD electrolytic capacitors are often marked with their capacitance and working voltage. Sometimes a code is used instead. SMD Resistor Coding. RS component or other electronic retailers. A micro-controller Unit MCU will carry out the control of the lamps.

    The inverter is linked to a lamp circuit consisting of a fluorescent lamp. The band or stripe indicates the positive terminal. The purpose of the analog circuits in the inverter is to transform a DC voltage input into an AC voltage at the output. Below example of SMD Capacitors will make this clearer. The MCU allows the same inverter circuit to drive multiple lamps while each lamp with the. In the design of Royer regulator. Direct Drive designs reduce transformer output voltage after ignition.

    Unlike the implementation of Royer regulator. Inverters must accept the dc input voltages. Said another way. In big picture. The result is creating an unity lamp brightness for systems such as LCD displays that require multiple lamps and where all lamps must produce the same level of intensity.

    A two lamp magnetic now in development will support up to Vrms strike and 12W operating power. This is equivalent to a 4 transistor full or H-bridge drive configuration and makes for very efficient operation at low voltages. For the backlight inverter board with Direct Drives. Direct Drive topology also enables efficient inverters that can run directly from 3.

    Direct Drive transformers will optimize for normal operation where they spend most of their life. The inverter controller receives the current sense and dimming input signals and generates an appropriate output for the inverter to produce the required AC voltage needed to drive the lamp. Small transformers can be used while system a CCFL is only present for the instant it is required.

    Gradually destroying the insulation material. With the new transformers and IC controller. The total power and the required strike voltage will limit the minimum size of this transformer. The Royer oscillator consists of two transistors. This is important method to test the backlight. To ignite CCFL lamps. You can use the spare backlight from another working LCD Monitor.

    It provides a healthy secondary power source from the primary power source. It provides an alternating current source to drive the lamp. In theory. Because it must operate at twice the normal lamp running voltage all the time. Knowing the good ccfl inverter voltage is critical to troubleshooting LCD Monitor. It depends on the number of ccfls are used. Numerous applications also expect efficient dimming capabilities to let lamp output to match surrounding light conditions and so extend the lifetime of lamp.

    For ccfl inverter voltage generation. No ccfl replacement is required. Replace new tube if you discover the dark end of lamp tube. To replace the backlight successfully. Be careful and good luck for your lcd monitor backlight replacement. Here is a typical lcd backlight replacement which the faulty lcd monitor is turning on and off cyclically then off permanently.

    Some backlight can be easily removed while some were tough. Always bear in mind. For totally sealed type backlight. You may plug it to another good Lcd monitor to ensure your cpu is in good condition.

    Double check any dark end on cold cathode tube. You can see brief OSD setup menu image appeared for while and black out. Suspect some parts went wrong over there. Confirm the transistor is faulty too. The adjacent NPN transistor next to it also was a bit shifted. If the fuse is blown. I turn 10 Check its terminal voltages. LCD monitor is switched on and working properly. Check other circuit transistors and it is quite warm.

    The culprit is the back heatsink Collector has been shorted to the line that connects to the Emitter. Notice the transistor was shifted from its original position. Confirm it with Atlas component analyzer to avoid wrong measurement. How to solder lcd monitor circuit board 1 Tools for soldering 2 Soldering safety and health 3 Photos for soldering dry joints on circuit boards 4 Basic soldering technique. C capacitor.

    In the following sections explains the basic soldering to advance soldering technique of the surface mounted devices SMD. Case 3: Solder out the faulty C I can tell you that approximately 40 percent of total faulty lcd monitors are easy to be repaired normally and the rest is a bit time consuming but it is worth to perform electronic component analyzing.

    R Case 2: Actually it is very easy to check if the problem is in the Main board, Start Circuit or even in the inverter IC itself. If there is a voltage say 2 to 5 Volts you can confirm that the Main board is working and sending a right signal. If no voltage measured by the meter then this indicates the Main board is having problem.

    If there are input signal to the base of the Start Circuit transistor and no output to the inverter supply pin, suspect defective components in the Start Circuit area or even a faulty Pico fuse preventing the supply voltage from flowing to the inverter IC. Do not overlook that a shorted inverter IC may pulling down the supply voltage to a very low value if the fuse did not open circuit. Do more practical testing on a good LCD Monitors and it would not take you long to find out if the fault is in the Main board, Start circuit or in the inverter circuit area.

    LCD MONITOR REPAIR - PDF Free Download

    Therefore, a backlight system that supplies the light from behind is normally required. The backlight system consists of a light emitting device that produces light, a conductor panel that distributes the light to the entire LCD surface uniformly, and a power supply that drives the light emitting device.

    Backlights can comes in many types of lengths and shapes too. The CCFL is called a cold cathode tube because even though the principle of illumination is the same as that of the hot cathode tubes used by indoor lamps, this lamp does not require preheating of the filament. Also, the electrodes at the end of the bulb stay at a low temperature while emitting light.

    CCFL also enjoy a long life approx 50, hours without serious degradation. This inverter is a small power supply used to make this CCFL illuminate, and is one of the important functional parts of a complete LCD display. Display Flicker and Reddish Normally a reddish display and display flicker in LCD Monitor were caused by one of the defective backlight either top or bottom backlight. For those LCD Monitors that do not have the feedback circuit in the inverter board, even though the backlight have problem the LCD Monitor continue to work and never shutdown.

    This is totally different in LCD Monitors that have the feedback circuit in the inverter board because even a slight flicker in the display caused by a defective backlight, the LCD Monitor would immediately shutdown. Some backlight can be easily removed while some were tough. For those backlight that had been totally sealed up, you must be careful when retrieving the back light.

    The TCP is very fragile and you should put more attention to it when you try to disassemble the LCD panel in order to check or replace the backlight. Once the TCP broken there is no way to repair it Questions related to the backlight 1 How do we know if a backlight is good or bad? By using another known good backlight either from a new backlight you bought as a spare or from another working LCD Monitor.

    If the backlight connector is compatible, just connect it and test. If the display is reddish or have flicker chances are high is the backlight fault.

    Again you have to remove the backlight and see if there is any dark end or not. Yes, you definitely can but again you have to check the intensity of the backlight from other LCD Monitor even though it is the same size of Monitor. If the replacement looks a little bit darker compare to the original backlight assuming you have replaced the top backlight then I guess you have to replace the bottom backlight too even though the bottom backlight is good for balance of light intensity purposes.

    Lcd Monitor Repair PDF

    You can keep the bottom backlight the good backlight for future use. You may check out the websites at the recommended resources in the last chapter of this book. It depends on your budget; you can order some to keep as spare and troubleshooting purposes. There would be no waiting time if you come across LCD Monitors that have backlight problem. Extra backlights may also help you to diagnose a problem fast. You will immediately know if the LCD Monitor problems like display shutdown, flicker, reddish, dim and etc were cause by a faulty backlight or not by replacing with a known good working backlight.

    Carefully observe from the screen at where the flicker starts first. If it start from 55 the top and spread to the bottom suspect a faulty top backlight. If it start from the bottom and spread to the top portion of the screen suspect a bad bottom backlight. Yes you can actually see at where the flickering starts first but with one condition, you have to focus and pay attention on the screen even if it takes you sometime.

    Once you have locate the defective backlight assuming the top backlight you will then replace it with a new backlight am I right? Well it is not always the case, sometimes for a minor flicker backlight problem you can actually modify the feedback circuit to make the LCD Monitor to continue to run without shutting down. The inverter board How I suppose to modify the feedback circuit?

    Trace from the bottom backlight feedback circuit and look for any resistor that goes to cold ground. Remove that resistor and replace it with a preset. I traced from the feedback circuit and found a resistor R that connects to cold ground.

    I remove the preset and measure the Ohm 57 value and it reads Ohm. I then replace the preset with a Ohm resistor and the LCD Monitor worked beautifully with no more flickering! However if the LCD Monitor have a very bad flickering and reddish the only way is to replace it with a new backlight. Please do not touch on a broken lamp with bare hands as it contains mercury.

    Mercury is known to be very poisonous to our human body! The whole purpose of the LCD panel is to controls light throughout using the liquid crystal material.

    Controller Board The purpose of the Controller board is to accept additional display information from the MAIN Board and then drive the column driver transistors and row driver transistors as to which pixel in the LCD panel should light or off.

    Backlight Generate a consistent, uniform light source. Polarizer A polarizer is a thin film that allows light to pass in only one orientation. Light Guide Plate LGP Light guide plates uniformly distribute light from the backlights, which are installed at the top and bottom of displays, over the entire screen.

    Replacement of LCD Panel If the LCD panel has problems such as cracked, white display, rainbow colours, bad controller board, one or few vertical lines, big horizontal black bar across screen, broken TCP and etc, the only way to solve it is to replace with a similar type of LCD panel.

    Most of my customers would sell it if you can offer them a much higher price. So what is exactly factory service mode?

    What are the internal settings in LCD Monitor? Some LCD Monitors have lots of internal settings while to some there are only a few ordinary functions.

    RGB colours balance, position, size, languages, information hours used in backlights and LCD panel and etc.

    What are the consequences if you have wrongly changed the settings in the factory service mode? If you have mistakenly set the wrong setting in the factory service mode you may end up ruin the display due to data lost and etc. We as a repair technician have to hold responsibility if the internal settings has gone out of value! Therefore it is advisable to write down the original value first before changing the setting in any LCD Monitors.

    If you are not sure about the functions settings then please do not change the value setting. This will surely benefit to those who wants to download the second hand or refurbish LCD Monitor provided if he or she knows how to go into the factory service mode.

    In general the less time hours that LCD Monitor used, it is better for a longer lasting operation. By the way not all factory service modes will display the manufacturer date. Again, not all LCD Monitor factory service modes will display such information. Will Factory Service Modes solve the no display, display shutdown and display shaking problems?

    How do we enter into the factory service mode in LCD Monitors? Different manufacturers have different way to enter into the Factory Service Modes. The login Factory Service Modes information are available only to the service technicians and engineers in the manufacturers and also to the authorized service centres but sometimes you can try login by pressing certain keys in the front panel control of the LCD Monitor. VO , colour settings and etc.

    You can either visit electronic repair forum to ask for the login details or get the LCD Monitor training manuals that have the login information or from your electronic repair friends. In a Plasma TV, the panel itself emit light, so the entire screen produces bright images with deep, expressive blacks under typical living room lighting conditions. The phosphoric elements lifetime in Plasma TV has been extended in recent years to give them a practical duration of up to 60, hours.

    That's eights hours of daily operation for more than 20 years before the screen reaches half of its original brightness.

    Plasmas also offer an advantage in colour saturation. Each pixel contains its own red, green, and blue elements, so they have what is referred to as very accurate chromaticity coordinates.

    Technically, resolution is limited on smaller plasma displays. Each cell, with its red, green, and blue phosphors, acts as an individual pixel. Recent plasma screens have caught up to LCDs in contrast ratio the measure of the relationship between darkest black to brightest white , thanks to newly developed internal algorithms that block the power going to particular pixels in order to render a pixel truly dark.

    This can produce contrast ratios up to 10, in the latest models. The light-blocking technology of commercial LCDs has kept them limited to contrast ratios of , although consumer versions will soon top This can be important or not: The impact on the viewer depends upon additional 69 factors such as overall brightness and ambient light. Tests have shown that even when looking at a contrast ratio of , most people's eyes are satisfied with the apparent level of blackness.

    LCD screens use a matrix of tiny liquid crystal cells sandwiched between sheets of glass or clear plastic, with a matrix of thin film transistors TFTs supplying voltage to the cells. When electrically charged, the crystals untwist to pass light from a source behind them.

    Depending on the degree of the twist, or polarization, the crystals block out specific parts of the colour spectrum the white light generates until they produce the desired colour by a process of subtraction. The white light source can be replaced when it grows dim, so the lifespan of LCD displays can be extended. Recent advances in LCD substrate material have also increased the practical viewing angle to between degrees to degrees.

    Some of the latest models can reach degrees, which rivals the viewing angle of most plasma screens. Our fingers are just too big for these little components. Please do not use a normal screw driver to force open the LCD cover as it may cause the plastic cover to have a mark on it. The best is to 71 split open a good tweezers into half. download a good quality tweezers because some cheap tweezers metal can bend over when you try open up the LCD cover. This tool is important to identify SMD component marking on top of its body.

    Without magnifying glass, you will have difficulty to recognize the coding of the SMD components. Get a 12 volts and a 24 volts rear light bulb to easily find out the faults in any LCD power supply problem fast. You need a set of small screw drivers in order to successfully open up the casing. Fishing Tackle Box- Yes, you may use a fishing tackle box or whatever box you found it to be good in storing all the tools for easy access when comes to troubleshooting and repairing LCD Monitor or even Motherboard.

    Removing and resoldering SMD components need this specialize tool. The first letter if present is a manufacturer code i. For example S3 is a 4. For SMD electrolytic capacitors are often marked with their capacitance and working voltage, e. Sometimes a code is used instead, which normally consists of a letter and 3 digits.

    The letter indicates the working voltage and the 3 digits 2 digits and multiplier give the capacitance in pF. Below example of SMD Capacitors will make this clearer. The band or stripe indicates the positive terminal.

    For example, a capacitor marked A is a 4. The purpose of the analog circuits in the inverter is to transform a DC voltage input into an AC voltage at the output. The inverter is linked to a lamp circuit consisting of a fluorescent lamp, a potentiometer, a current sense resistor and a rectifier diode terminal of the potentiometer is connected to the inverter controller, which is also part of the lamp circuit.

    In the design of Royer regulator, the lamp ballast capacitor is usually in the range of 12 to 22 pico Farad in order to drop excess transformer output voltage after the lamp has ignited. A micro-controller Unit MCU will carry out the control of the lamps. The MCU allows the same inverter circuit to drive multiple lamps while each lamp with the individual dimming control is reserved.

    The result is creating an unity lamp brightness for systems such as LCD displays that require multiple lamps and where all lamps must produce the same level of intensity.

    The inverter controller receives the current sense and dimming input signals and generates an appropriate output for the inverter to produce the required AC voltage needed to drive the lamp.

    For the backlight inverter board with Direct Drives, the main advantages of the pushpull transformer are its dual primary winding construction which the voltage impressed across the primary in Direct Drive modules which are twice the supply voltage. Direct Drive topology also enables efficient inverters that can run directly from 3. This is equivalent to a 4 transistor full or H-bridge drive configuration and makes for very efficient operation at low voltages. Unlike the implementation of Royer regulator, new approach of Direct Drive for lamp strike voltage generation relieves the transformer from operating continuously at full lamp strike voltage once the lamp is ignited.

    Direct Drive transformers will optimize for normal operation where they spend most of their life. Small transformers can be used while system a CCFL is only present for the instant it is required.

    Gradually destroying the insulation material, high voltage corona discharge can be more easily avoided with Direct Drive designs. With the new transformers and IC controller, the backlight inverter board of Direct Drive has been developed completely which the first two are 6 watt units that can drive lamps having strike voltages of up to Vrms.

    Lcd Monitor Repair PDF

    A two lamp magnetic now in development will support up to Vrms strike and 12W operating power. Clearly, strike capability is enhanced while transformer size and reliability are improved. In big picture, Direct Drive designs reduce transformer output voltage after ignition, permitting ballast capacitance values to be much larger.

    Now you have learned the direct drives backlight inverter board. You will be more familiar with the inverter board when you have chances to open out the LCD monitors casing and observe it yourself. Inverters must accept the dc input voltages, typically 12V, and provide ac outputs of to V to run the lamps.

    To ignite CCFL lamps, these circuits must supply short strike voltages that typically are double that of their working voltages. Numerous applications also expect efficient dimming capabilities to let lamp output to match surrounding light conditions and so extend the lifetime of lamp. It depends on the number of ccfls are used, inverter circuits combine with single, dual or quad high voltage transformer to generate the high voltage required for ccfls.

    For ccfl inverter voltage generation, the inverter circuit with the buck regulator consists of two power semiconductors, one power inductor, a PWM regulator IC, and a high current capacitor. It provides a healthy secondary power source from the primary power source. The Royer oscillator consists of two transistors, a high-current resonance capacitor, a high-voltage transformer, and a ballast capacitor in series with the lamp.

    It provides an alternating current source to drive the lamp. The current amplitude is controlled by the ballast capacitor through the lamps negative impedance which dropping an approximately equal voltage across its positive impedance. In theory, the lamp current will be the total transformer output voltage minus the lamp voltage lamp voltage is inversely proportional to current divided by the capacitors impedance. The total power and the required strike voltage will limit the minimum size of this transformer.

    Because it must operate at twice the normal lamp running voltage all the time, its size must support full strike power and voltage, even after the lamp is ignited. Knowing the good ccfl inverter voltage is critical to troubleshooting LCD Monitor. You can use the spare backlight from another working LCD Monitor. This is important method to test the backlight.

    Otherwise, you will waste time and money if the fault is on the inverter circuit or dry soldering and etc. Normally, the backlight fault will be suspected when you found the display is flickering or discoloring.

    Double check any dark end on cold cathode tube. Replace new tube if you discover the dark end of lamp tube. To replace the backlight successfully, you must pull out the backlight gently together with its casing.

    Some backlight can be easily removed while some were tough.

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