not require an. I do suggest you read more on SMPS and how to repair them because it will definitely speed LCD TV Power Supply (IP BOARD) Schematic. LCD Monitor Repair Brought to you by Jestine Yong http://www. osakeya.info osakeya.info http:// www. The reader is expressly warned to consider and adopt all safety precaution that might be indicated by the activities herein and to avoid all potential hazards.
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Download LCD MONITOR REPAIR GUIDE service manual & repair info for To open downloaded files you need acrobat reader or similar pdf reader program. 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. LCD MONITOR REPAIR MANUAL PDF The main topic of the following pdf is centered on LCD MONITOR REPAIR MANUAL PDF, but it did not.
A breaker is a simple and an inexpensive fix. Led Tv Circuit Diagram. Please verify that the power supply board inside your LCD monitor or TV matches this power supply board before ordering! Circuit breaker—A blown breaker could also be the cause of your power issues, so check your circuit breaker box. Samsung tv parts diagram wiring diagram data mining cost service manual, circuit diagram led vu meter, schematic diagram of 9 volts power supply, led monitor schematic diagram, gateway laptop service manual free, suzuki b-king service manual download, circuit diagram power bank, service manual sony kdf-e50a10, Lcd Tv Power Supply Schematic Diagram solution for an LCD TV power supply.
Free Shipping on all boards. Power supply is a good MFL Go to that page to read the explanation about above power supply. Toshiba xv xvda lcd tv power supply schematic samsung led tv circuit diagram. LG over the last few years has ceased to publish diagrams of power supply units from their TV.
For your information I used to understand an equipment block diagram first before i go into the schematic and analyze the circuit functions. This video is based on how to repair led lcd power supply in very easy way how to PFC circuit work in lcd led power what is the role of PFC circuit in power LG Diagrams, Schematics and Service Manuals - download for free!
You can already Power Board. Open 7 days a week. Our television parts are back with an industry-leading warranty and price beat guarantee! Our goal here is to provide an overview of the basic types of circuits used to power LEDs. Visit the post for more. The reference design circuit consists of one single-sided. On site Technical Support. Ask your LG questions. Note that all these links are external and we cannot provide support on the circuits or offer any guarantees to their accuracy.
Motorola offers a wide range of power supervisory circuits that fulfill these needs in a cost effective and efficient manner. Circuit Board Diagram. A Switch Mode Power Supply.
Incorrect adjustment can cause the picture to be too dark or too bright. If the supply is still inoperative, the integrated circuit may be bad. How to build your own Power Supply. Locations of the test points and adjustments on a typical SMPS power supply. Part one: is composed of 18 chapters of the major circuit blocks in CRT TV and a circuit diagram of the LG television any because mostly TV circuit diagram for a in electronics sometimes if you don't have the Samsung tv parts diagram.
Schematic Circuit Diagram Lg lcd tv schematic diagram. LG standard crt televisions colour tv circuit diagram related questions and answers. Multiple output switching power supply circuit schematic diagram schematic of the display s power supply is below graphic regulated high voltage power supply circuit diagram lg ctv circuit diagram vra impression picture grundig lcd tv power supply 04 Lg Tv Circuit Diagram - See more about Lg Tv Circuit Diagram, lg colour tv circuit diagram pdf, lg crt tv circuit diagram, lg crt tv circuit diagram pdf, lg flatron Visit the post for more.
Power amplifier schematics 7 lg led tv schematic diagram. LG TV. Samsung TV Schematic Diagram. HP VS19E. I have a spare power supply with a socket in it that I use exclusively to test integrated circuits. Connect the replacement transistor leads to the corresponding leads extending from the circuit board and crimp the "U" with long nose pliers to insure metal to metal contact then solder each connection. The circuit diagrams, or schematics, that follow are drawn using industry standard electronic symbols for each component.
This post has been written by Vishwam, an electronics geek and an awesome guitarist. Therefore, understanding the different types of tuner would be useful if we want to replace the tuner with the other models. LG do you have a download back program for this model??? Clearly there was a defect. There are 4in1 amplifier module in a circuit board.
Bend into a "U" shape the replacement transistor leads. Original panasonic power supply tnpa power board plasma tv flat original panasonic power supply tnpa power board plasma tv flat tv parts lcd led tv parts boards tv board tv from dhgatedpdpstore dhgate.
Using the wrong type of power supply can not only damage your LED product but can also be a very dangerous fire hazard. It powers on and there's sound, and when I light a flashlight on it there's an image. LG color tv 21 inch Circuit Diagram schematics datasheet, cross reference, circuit and application notes in pdf format.
Skema samsung ln 26bf1 ln 32bf1 tft lcd tv circuit samsung led tv circuit diagram. The other stage consists of a tuning capacitors, high voltage transformer, and push-pull transistor pair to boost ac output to hundreds of voltage. The ballast capacitor controls current amplitude through the lamp negative impedance by dropping an approximately equal voltage across its positive impedance. The feedback circuit is for protection purposes and will shut down the inverter IC just in case if the high voltage produced by the high voltage transformer exceeded the normal value and also it can detect bad or a flicker backlights.
The AC frequency of the high voltage transformer is typically run at 30 to 70 KHz. The higher the frequency, the greater is the light output. The common push pull transistors part numbers are C, C and etc. The expanding magnetic field in T1 induces a voltage across T1 38 secondary.
When Q1 turns off, the magnetic field in T1 collapses and after a period of dead time dependent on the duty cycle of the PWM drive signal , Q2 conducts, current flows through the 'lower' half of T1's primary and the magnetic field in T1 expand. Now the direction of the magnetic flux is opposite to that produced when Q1 conducted.
The expanding magnetic field induces a voltage across T1 secondary. After a period of dead time, Q1 conducts and the cycle repeats. The above diagram only showing a single channel IC that is driving the Q1 and Q2. Some inverter IC can have two channels in order to drive two high voltage transformers.
Each output from the transformer can drive more than one lamp. Please take note of this! The reversal of the magnetic field is achieved by reversing the direction of the primary winding current flow. This type of inverter is found in many LCD Monitor too. The control circuit of a half bridge inverter is similar to that of a push-pull inverter.
This design has optimal utilization of transformer core and primary winding one vs. Please take note of this too! A Half Bridge inverter schematic 4 Full Bridge Inverter Direct Drive 40 The full bridge inverter is similar to the push pull inverter, but a centre tapped primary is not required.
This type of inverter is found in many latest LCD Monitors. Diagonal pairs of transistors will alternately conduct, thus achieving current reversal in the transformer primary.
This can be illustrated as follows - with Q1 and Q4 conducting, current flow will be 'downwards' through the transformer primary and with Q2 and Q3 conducting, and current flow will be 'upwards' through the transformer primary. The control circuit monitors V out and controls the duty cycle of the drive waveform to Q1, Q2, Q3 and Q4. The control circuit operates in the same manner as for the push-pull inverter and half-bridge inverter, except that four transistors FET are being driven rather than two.
The main control signal comes from the Main board and the voltage is from 0 and few Volts 2- 5 Volts. The Start Circuit is a good starting point to diagnose why the LCD Monitor has no display, display shutdown and intermittent no display problem. Example of Digital transistors I received many emails asked about how to diagnose LCD Monitor problem that have power but with no display symptom.
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. 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. 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, The light-blocking technology of commercial LCDs has kept them limited to contrast ratios of 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 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. Here are just some of the tools that you must have in your technical department: 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. With such testers you will surely have more confident in repairing LCD Monitors. Do not use a screw driver to open the cover as it would definitely leave a deep mark on the plastic cover.
The plastic cover is not that really hard and the moment you use a screw driver to peel out the cover, the soft plastic would be dented. The metal you can actually use one from a split tweezers. Do not get a cheap tweezers as the material is quite soft and would not hold on at tight LCD Monitor cover.
download a quality tweezers and break open it into two and use the end to peel off the cover. Always start to remove LCD Monitor cover from the bottom. Once the bottom corner cover had been removed, you then can start to peel off the cover at the side and eventually to the top and another side of the cover.
In some LCD Monitors, you can use both of your hands to gently but with a little bit of pressure to remove the side cover. Look at the photos next page for easy reference. Each SMD resistor has a numeric number on top of its body.
It would not take you a long time to understand it as the below guidance will show you exactly how you can calculate the ohms value easily. SMD network resistor is actually consisting of few resistors that have same ohms value in a single package. Calculate the SMD resistor code first, once you have the value then only you test it with a digital meter. Place the test probes across the two ends of the SMD resistor on board and read the result directly from the digital meter LCD display.
Usually SMD resistor is very robust rarely give problem in the Main board but not in power supply board. Certain brands of LCD Monitor power supply board do use SMD resistors and once if there is any problems in the power supply surge, short circuit and etc ; some of the SMD resistors may get burnt!
Once the SMD resistor burnt, the only way to find out the value is through schematic diagram and comparison from the same LCD Monitor model. You may call up your repair friends to ask if they have the same model of Monitor or not to find out the real value of the burnt resistor. If the body was black with the letter A, it equals 10pF. Pentax Leadless Capacitor Values. Others manufacturers have their own code thus making us as a repair technician have difficulties in finding the SMD capacitor value.
There is one way where you can find out the capacitor value. Assuming you found a red colour SMD capacitor shorted in a LCD Monitor Main board, what you can do next is to look around the surrounding circuit for the same size and same colour of the SMD capacitor. Remove it out from the circuit and measure the capacitor value; once you got the value you can then replace a new capacitor on the shorted red colour SMD capacitor.
I have done that before and it worked! The first way is to use specialize test equipment that was designed to test SMD components like the famous Smart Tweezers by AdvanceDevices.
I found that the result were not that accurate when measuring the SMD capacitors on board most probably due to back circuits and you need to solder it out and test off board for accurate reading. In order to get a good result we have to solder it out and test. The only disadvantage using this way to test SMD capacitor is the probes are too big for the small component. Anyway it should not be a problem to us as electronic repairer as we could easily modify the probes to test the tiny components.
Sometimes by measuring only the capacitance value will not guarantee that the capacitor is good and you need to perform another test to make 90 sure that the capacitor is not breaking down when under full load.
How are we going to do that? The third testing method will answer your question. By using analogue meter set to X10 K Ohms we can accurately test SMD capacitors that breakdown when under full operating voltage.
Just place your test probes across the capacitor and the pointer should not show any low ohms reading. If the capacitor value is big, it may cause the pointer to kick up a little and go back down to its original position infinity.
Swap the test probes and retest again and you will still get back the same result. This proved that the capacitor is working fine! Take note: No matter what types of SMD capacitor you are measuring, the pointer should not stay at low ohms reading either way test probes you test it with analogue meter. Conclusion- In order to successfully confirm that a SMD capacitor is good, you must perform two tests; first is to measure the capacitance value and the other one is to check the capacitor with analogue meter set to X10 K ohm and make sure it is not shorted.
A 3 legs SMD diode you may think is a transistor. A digital transistor you may think it is a normal transistor and so on. If you do not know the meaning of the codes, I believe you will have a hard time to test the components. A good component you may think it is bad and this will eventually cause you to lose more of your troubleshooting time in electronic repair. You have to visit this website http: Once you know what type of components the codes belongs to, then you can use the necessary testing method to check it.
A good SMD diode should have one reading and if you get two reading that means the diode already shorted. You also have to beware that SMD Schottky diode would have two reading but not shorted reading. Please refer back to testing Schottky diode chapter to learn how to test a Schottky diode. You may also do your own research to find out if a device that have 3 legs is a voltage regulator or not by performing some voltage testing.
Sometimes a 3 legs device could be a Mosfet so please take note on this. Just be alert and flexible. If you observe any electronic schematic diagrams and layout, Schottky rectifier symbol looks exactly the same as a normal diode. Typical Schottky Diode 99 Even the outlook, shape and designed just like a normal diode. The major difference between a normal diode and Schottky barrier diode is the part number. Because of the same outlook, many electronic repairers think that measuring Schottky diodes is just the same way as testing a normal diode.
If you use the normal diode checking method to test on Schottky diode then chances are high that you will not solve the problem. You also find that it was quite common in LCD Monitor to see two Schottky diodes in a single package as shown in photo below.
Both Schottky diodes are pointing to each other and the testing method is just the same as when you are checking a single diode. I will show you the right method to test Schottky diode so that you will not confuse anymore. Using the semiconductor data book and with the help of search engines, you will easily find out whether the diode you are checking is Schottky, normal diode, ultra fast recovery or even damper diode.
Once you have confirmed that the diode you are going to test is a Schottky diode then you have to use the right way to measure it. Using analogue multimeter, set to X1 Ohm and place the red probe to centre pin and the black probe to either side of the pin, you should get a low ohms reading.
Now reverse the probe where the black probe to centre pin and the red probe to either side of the pin and should not get any reading. If you get a reading then the Schottky diode is considered shorted. You should see the pointer moved to full scale.
Now, reverse the probe and you will get some leakage reading. In other words, the pointer will move up a little bit. This is the good characteristic of a Schottky diode when you get this type of reading. However if you test a normal diode using the X10 K Ohms range and you discovered that it has two readings then the diode is said to be defect and need replacement.
Sometimes replacing a Schottky with a normal diode may cause the equipment to be unstable especially in the sensitive circuit. The best is to replace with original part number or a specification that is higher voltage and current than or same spec with the original diode.
Refer to your favourite semiconductor replacement book for datasheet and find out the specification of these part numbers. If you have one, try testing it with your analogue meter and you will be surprised that there are two readings at X10K Ohm but not shorted reading. By the way the failure in Schottky diodes were quite common thus you have to know what you are measuring. This can often be fixed. What is a stuck pixel? A stuck pixel is a common pixel defect on LCD screens.
A stuck pixel is a bright dot of colour on a screen which emits colour when it is not supposed to. Stuck pixels are most easily noticed on dark or black screens where it will appear red, green, blue, or any combination of the three colours including yellow, purple or even white. Solid red, green, or blue, are the most common stuck pixels. Many people often falsely labelled stuck pixel as dead pixel, whose one of the three sub-pixels are permanently off, producing a black pixel.
Each pixel on an LCD screen is composed of three cells sub-pixels , one red, one green, and one blue, which produce the visible colour of the pixel by their relative brightness.
A stuck pixel results from a manufacturing defect which leaves one or more of these cells turned on. Stuck pixels are not easily noticeable on a white background and you need to make sure that the background is dark black in order to locate stuck pixel.
Visit this website http: How to fix stuck pixel? Pressure Method 1. Gently apply little pressure massaging on only the stuck pixel area otherwise you may create more stuck pixels.
Continue to apply the pressure on the stuck pixel until it totally gone sometimes the stuck pixel may appeared again so you have to do it few more rounds. If the stuck pixel is still there even after you have used the pressure method then I guess you have to use the software method. Try running pixel fixing software where you can get it at www. Stuck pixels can often be re-energized by rapidly turning them on and off.
If the LCD Monitor is under warranty then you have to inform your supplier about this but usually the supplier only will replace if there are more than 10 stuck or dead pixels in the LCD screen! What is a dead pixel and how to fix it? A dead pixel is a defective pixel that remains unlit on an LCD screen.
Dead pixels are always black and are most noticeable on a white background. A dead pixel occurs when the transistor that activates the amount of light that shows through all three sub-pixels malfunctions and results in a permanently black pixel. Dead pixels appear black while stuck pixels can be one constant colour like red, blue or green. Dead pixels can not usually be fixed. However, you still can use the method fixing stuck pixel and try on dead pixel.
Do not attempt to open the LCD Monitor as it will void the warranty and the manufacturer will not replace it. Make sure you don't get any electrical equipment wet. Do not apply too much pressure on LCD screen as it can break crack easily. Sometimes if you are not careful and applied too much force on it while cleaning the LCD panel, it may crack also. Is there a way to repair a cracked LCD panel? For your information no one can repair cracked LCD Screen.
Replace only with the same size and model. The liquid crystal that may leak from the panel is poisonous if it enters the eyes or mouth. If any part of the skin or body parts comes in direct contact with the panel, please wash thoroughly.
If some physical symptoms result, please consult your doctor. Many professional electronic repairers use test points to locate fault to the exact location. Here you will have the opportunity to learn voltage testing and start to identify faulty section in LCD Monitor. Danger - Before you begin to test any points in the LCD Monitor, I highly suggest that you get help from your experienced repair friends and make sure the AC Voltage is coming from an isolation transformer so that it can protect you just in case if there is any electrical shocked happen.
Treat electricity with respect and make sure you are completely known what you are doing. First locate the bridge rectifier and then place the test probes across the AC pins. Since you are measuring the AC voltage the test probes can be in either way.
If it is zero volts then you have to check the circuit before the bridge rectifier. Please make sure you hold tight to your test probes and carefully touch on the capacitor pins. If you accidentally touch the pins while doing the test, it might generate a great spark and blow the power section. The black probe has to be at the negative pin side and the red probe to positive side as shown from the photo. You get DC voltage because the bridge rectifier already converted it from AC supply.
If you get the expected DC voltage then move on to test the supply voltage of the power IC, if not troubleshoot the area to locate if there is any problem with the circuit like dry joints, broken track and etc. In the below photo, we got If you get the right voltage this mean that the bridge rectifier, filter capacitor and the start up resistors is doing its job and you should now perform the next test.
You should get a DC volts reading from all the secondary output diodes. If you spend your time testing the components in the power side, you are just wasting your time. Since there is correct voltages presence at the secondary outputs, your next step would be finding faults that are located after the secondary output diodes.
Just place the red probe to the output of the voltage regulator normally pin 3 is the output pin and read from the meter. If it show 2.
If not you have to start troubleshoot backward from the input pin pin 1 and sometimes the voltage regulator itself can be defective too! If the voltage is not present or too low for the inverter IC, the LCD Monitor would not have display dark display or even intermittent shut down.
Thus it is important to make sure that the inverter IC must received a steady voltage from the power supply. The driven pulses are usually 20kHz to kHz with variable duty cycle. In the transformer secondary will generate a voltage pulse train with varying magnitude and duty ratio. Now, you got the idea of the lcd monitor repair with mastering the working principle of lcd monitor circuits. The indication of the monitor is no power and blank screen even though the external power supply is plugged in.
After I have listened to his words, I do a quick test on the monitor in front of him to double-check the problem. Exactly, the monitor has no led power lit when switch on the power supply. He requests me to repair the monitor as soon as possible because this monitor brings him lots of winning on stock trading.
He wishes to use the same setting so that he can win the trade in the stock market. I reply to him confidently that he will be able to receive his monitor next 2 days or early. Then, he walks away happily. Because, I have similar experience on the same model of the monitor and good understanding of circuit operation especially on the switching mode power supply. There is a systematical method I will tell you right here on how to analyze and repair LCD monitor no power in simple and quick way.
Is the fuse blown? Immediately, I unscrew the outer and inner covers of LCD monitor. Please ensure no power connected to the monitor. The first place to be checked is on the power supply board. I measure the continuity of the fuse and Both of them are in good resistance. After that, I inspect all capacitors, resistors, inductors, diodes and ICs are in good shape. For a quick test, I plug in the power cord and switch on the monitor to do the voltage testing.
I use the voltmeter to measure the 12 Vdc output of the secondary transformer Guess what do I find out?
No DC voltage is measured right here. This means the primary section of transformer is not functioning which there is no pulse is provided by the power IC to the transistor and followed by the rapid switching of the transistor to induce the transformer in normal operating condition.
I guess a high probability fault on primary circuit of power supply board. Download the guide on the theory of the switched mode power supply for your reference. Now, I will check two important voltage test points on the primary circuit which are the big filtered capacitor and Power IC , pin 1. I got reading Volts on in good condition but the input voltage to IC pin 1 is 6 volts only. In normal operating condition of IC , the input voltage must be at least 11 Volts or above to start up and oscillate itself internally.
Surprisingly, the voltage across the resistors has fallen to half value of 16Vdc. I switch off the power supply immediately and de-solder the resistors and diode from the circuit board. I got the resistance value changed to K ohms each resistors and the diode is ok. According to Ohm law, the resistance that increases will result the voltage drop.
I have the spare resistors and replace the resistors in same specification properly. Within my expectation, the LCD monitor now is returned to normal condition. I leave it run for few hours. Finally, I call the customer to collect the monitor next morning. He receives the monitor happily and gives his appreciation to me.
The whole process of the testing and replacement is only taking 1 hour approximately. I can earn dollar in the short period based on my experience and good knowledge of the working principle on LCD monitors. Now, you can grab this opportunity to learn the systematical method from this book which compiles a step-by-step and headto-toe practical guidance in photos for smps repairing of LCD monitors.
You too can become a professional repairer and earn lots of money from this kind of repair. The answer is always yes with you invest your time and energy to learn the knowledge of basic electronic component testing and learn the working principle of the lcd monitor circuits and stay focus in Lcd monitor repairing.
Always remember your safety first. To become a successful lcd monitor repairer, you must study the knowledge of the electronic component testing and its characteristic such as various type of fuses, resistors, capacitors, inductors, diodes, transistors, integrated circuits and etc. This is a very important step to analyze which electronic components incurred in the lcd monitor fault.
The wrong analysis of the electronic component testing will waste your time and energy. But, prior to testing the electronic components, you must know the basic electronic component coding which is an essential and initial part for the correct interpretation of measurement and testing on Lcd monitor circuits. SMD Resistors are usually coded with a numerical equivalent of the familiar three band color code.