LCD TV repair failure general processing

General LCD TV repair process:

1. During standby, the power supply board only provides a 5V or 3.3V power supply to the CPU. The other 12V.18V.24V.9V voltages must wait until STANDBY is turned on. This time, the CPU needs to send a high level 5V or 3 3V to the power board, the power board is connected to the voltage sent by the CPU before starting 12V, 9V, 18V.24V voltage, if the voltage of the power board is normal, basically the power board is OK.

2. After the CPU board is powered on, the 5V voltage provided by the power supply board is sent to some chips for power supply through some 3.3V, 2.5V, 1.8V chip regulators. Don't underestimate these low voltages. Many times later, these voltages are a little higher (0.7V), which will cause black screen and no grating faults. Usually the damage is caused by the deterioration of the filter capacitors of these regulators, or the main killer of strange faults after aging. Generally, the decoding integration (digital conversion IC) of the liquid crystal is powered by 3.3V and 1.8V, and the power supply of the register connected with the decoding is 2.5V. When the LCD is used for about 1 year, these decoding integrations are often prone to occur. The problem of solder joint failure, this time to test everyone's welding technology level, the practice has proved that part of the repair is to repair the fault.

3. The black screen fault is not the most common fault of the LCD after no grating or grating flash. This fault can generally be judged by measuring the voltage. After the remote control is turned on, it is normal to measure the power supply of the power board. To the backlight board connection line ON / OFF pin voltage is not high 3.3V, and then test the PWM pin voltage is also about 3.3V, if it is normal, then the screen should be the backlight board is faulty, If these two voltages are not available, then the problem is that the decoding integration does not work or the software does not run up, then the CPU board must be repaired.

The above is just a small part of the experience of repairing flat-panel TVs. If you want to repair it quickly, you still have to spend more time to hone. I hope everyone can become a master of flat-panel LCD TVs.

LCD TV common fault judgment method

Now LCD TVs are the main products of major manufacturers. Ordinary CPT TVs have gradually withdrawn from the market. Therefore, it is imperative to master the skills of LCD TV maintenance as a maintenance person. The following is my experience and good work in maintenance. Exchange, I hope more such articles will appear in the future.

To repair the LCD, we must learn to judge that part of it is faulty, this is a step by step. Here are the main faults and parts of the LCD TV.

1: There is no sound in the boot, the power light flashes into a constant light, and the screen flashes white light when it is turned on. This fault is mostly caused by the backlight drive board damage. However, it has also been seen that the lamp inside the screen is damaged during maintenance. .

2: After the start-up, the flower screen (mosaic) is sounded. The sound is normal. This phenomenon is a bad digital board (the hole is not connected or the IC contact is not good). The second is that the connection inside the machine is not good.

3: Boot three no, the power light does not light. Brother one is the power board is bad, the younger two is the CPU part is not working properly.

4: The light flashes and cannot be turned on: the CPU bus is not working properly or the boot program IC (BIOS) is bad, and the "BIOS" IC and the CPU are not in good contact.

Judgment and repair of various components of the plasma screen

Like ordinary TV sets, the high-voltage parts of plasma TVs are also in the power board and driver board. The reason is that these parts are working in high voltage and high current conditions. Since the current maintenance of the plasma TV is a board-level maintenance, in the actual maintenance, only the faulty component board or circuit board needs to be judged, and the components on the component board need not be repaired. And replacement. Just because: on the one hand, the components in the plasma TV circuit board are mostly imported, which cannot be purchased in China or the manufacturer of the screen; on the other hand, the various circuit boards in the plasma TV are multi-layered. Structure, maintenance under non-factory conditions, it is easy to create new faults on the board due to poor disassembly, so the current plasma TV,

LCD TV repair, the entire industry is performing board-level maintenance, that is, changing the entire component board.

When repairing, detecting, and disassembling the circuit of the PDP panel, it must be noted that the large-capacity capacitor has been discharged. Pay attention to the difference between cold and hot ground when detecting voltage, and pay attention to anti-static or ESD.

For the judgment and detection of the power board, firstly, it should check the output voltage of each power board, whether it is the same as the label attached to the top right corner of the screen (at this time, the sticker is shown to everyone), if the measured voltage Unlike the on-screen standard, it is very likely that: 1. The power board itself is damaged, causing the voltage and the screen to be different; 2. The load on the power board is problematic, causing the output voltage of the power board and the on-screen label to be inconsistent. . We can first check the voltage value of each socket output from the power board. If the voltage value on the socket is abnormal, unplug the plug wire on the socket and disconnect it from the rear-end circuit. Then measure the power socket. The output voltage, if the voltage is normal, indicates that there is a problem with the board of the latter stage, and vice versa. One thing to note is that the VS voltage is output on both sockets here (indicating the position of the two sockets at this time), so if the VS voltage is abnormal when the plug is pulled, It is also necessary to unplug the VS voltage plug on the other side to determine whether it is a power board or a board problem in the latter stage. [Page]

In actual maintenance, the most common fault of the power board is that there is no drive voltage output or the drive voltage is too low, resulting in a black screen (black screen means the entire screen is not lit, or there is sound or no sound). By detecting it, it can be found that the VS driving voltage has dropped drastically, and the VSC driving voltage has dropped to about 0V. PS42D8 power board, in the actual maintenance, you do not need to bring a dummy load, you can test the machine, so maintenance will be very convenient. When we suspect that there is a problem with the power board, we can unplug all the plugs of the entire power board assembly, remove the power board assembly, and short the 3rd and 4th feet from the left of the CN802 (or CN9004) socket on the power supply board. Then, the power supply board is powered by 220V (this is required to be demonstrated). If the power board component is good, all the sockets of the power board will be output and printed on the printed board after the power is turned on. The same voltage (with a certain deviation, but the deviation value is small), as long as one voltage or a group of voltages is different, the power board components are bad.

If the X drive board of the screen is broken, the following faults may occur: 1. The image is very dark or has no contrast or the layering is poor; 2 There may be a black screen; 3. There are colored patches on the image. If the X drive board is suspected to be broken, the board can be disengaged from the circuit. If the X drive board is removed, the image is almost unchanged, that is, the X drive board is mounted and not mounted. At the time, the X drive board may be bad. Or you can replace it with a good X drive board. Whether the fuse on the X drive plate (in this case, the position of the fuse) is blown can also be a basis for damage.

If the Y drive circuit board of the screen is broken, the following fault phenomenon may occur: 1. Black screen; 2. Black screen in the upper half or black screen in the lower half; 3. Flower screen (image is disorderly); 4. Horizontal bright line or black line Or bright band or black belt; 5 upper half bright screen or lower half bright screen; 6, burn Y upper and lower siting circuit board. Whether the fuse on the Y drive plate (in this case, the position of the fuse) is blown can also be a basis for damage.

Common phenomena of logic board damage are: 1, flower screen; 2, black screen; 3, vertical or horizontal lines or vertical or horizontal bands in horizontal and vertical directions; 4, control failure; 5, no image, etc.;

The COF location circuit and the COF plug are damaged. The fault phenomenon is vertical or vertical bright band in the vertical direction, or vertical black line or vertical black band. On the Samsung V2 screen, you can also see the damage of the appearance of the soft-package integrated circuit on the COF plug, such as the air drum, the blowout hole, the blackening of the integrated circuit, etc. (At this time, if the demonstration is Samsung V2 screen In addition, it should also demonstrate how to look at the good or bad of the integrated circuit on the COF.

1. One appears on the screen, or several horizontal lines are not bright:

Check if the socket between the Y drive board and the Y board (buffer board) is plugged in. If it is not plugged in, reinsert the socket. If it is already plugged in, it will appear on the top and bottom of the screen according to the dark line. Replace Y ( Buffer board) (upper and lower)

2. One on the screen, or several horizontal bright lines that are brighter than the remaining horizontal lines on the side:

Check if the socket between Y drive board and Y (buffer board) is plugged in. If it is not plugged in, re-plug the socket. If it is already plugged in, it will appear on the top and bottom of the screen according to the dark line. Replace Y (buffer) Board) (upper and lower)

3. A vertical unlit line appears on the screen, or a vertical vertical block

a. If there is a vertical line that is not bright, there is a problem with the COF.

b. If there is a vertical vertical non-bright block, first check if there is a problem with the connection socket between the COF and the addressing circuit. If there is no problem, check whether the connection socket between the address circuit and the logic board is normal. If it is also normal, replace the address board. Finally, after the replacement, if the problem cannot be solved, replace the logic board.

4. When a monochrome signal is displayed on the screen, one or several bright lines of other colors appear vertically:

a. If there is a vertical bright line of other colors, it is a COF or a problem with the screen.

b. If there is another vertical bright color block, first check if there is a problem with the connection socket between the COF and the addressing circuit. If there is no problem, check whether the connection socket between the address circuit and the logic board is normal. If it is also normal, replace the address board. After the replacement, if the problem cannot be solved, replace the logic board. Finally, if the problem of replacing the logic board is still there, there is a problem with the COF.

5. The screen has a dark grating, which is not bright, and can be blurred to see the image:

If there is no output from the screen drive voltage of the power board, check whether the voltages such as VS, VSC, and VA are normal. If not, check if the logic board VS_ON pin is 2.8V after power on. If yes, the logic board has been controlled. You can pull up the corresponding socket of the power board, judge whether the power board is still a load problem, and replace the corresponding board.

6. On the screen, there are abnormal highlights that are different from the above, bright blocks, etc.:

a. Check whether the socket between the address board and the COF board and between the logic board and the address board is connected.

b. Replace the address board and replace the logic board if it cannot be solved. If the problem is still there, there is a problem with the COF. [Page]

7. No grating, the indicator light is red, and the blue fault is judged.

First check the screen to determine whether it is a screen or a board problem. If the screen is changed, if the board can detect the SCL and SDA bus voltages, the fault range can be determined by the bus voltage as follows: If the voltage fluctuates around 2.4V, the IC connected to the bus on the main board will fail, such as AD9887, VPC3230. , PW1230, etc., can check the power supply and IIC path of each IC first; if the voltage fluctuates around 1.8V, the communication between the main CPU PW181 and the sub CPU SDA555 is abnormal, and it can check whether the RXD and TXD are faulty. If the voltage fluctuates around 0.8V, the memory and FLASH chip of the PW181 are faulty.

f. No grating, the indicator light red and blue lights are not bright.

If the red and blue lights are not lit, the SDA555 itself is generally bad, and the PW181 itself may not be powered or not working. After the failure of the Samsung Y driver board, these phenomena have appeared.

1. Can not open, the indicator light does not light.

2. Flower screen

3. The screen is dim, only the blurred image

4. Boot for a period of time, no picture is silent, the indicator light is blue. Shut down and then turn on, normal

PDP maintenance considerations ------ internal training materials

PDP maintenance precautions

In order to avoid possible danger, injury or physical injury, and to avoid new damage to the PDP screen, the maintenance personnel must read the following terms carefully. If you ignore the following warnings, it will cause fatal injuries:

1. Different models have different screens and cannot be replaced directly. Be sure to replace the original model.

2. The PDP module (including the screen, driver circuit, logic circuit and power module) operates at approximately 350V. If you want to operate the PDP module during normal operation or just after power failure, you must take appropriate measures to avoid electric shock and do not directly touch the circuit or metal part of the working module. This is because the capacitance of the drive section remains high for a short period of time even after the power is turned off, so even after the power is turned off, you must ensure that the operation is performed at least one minute later.

3. Do not give the module any power supply that is higher than required in the specification. If the power you are using is deviated

The values on the data sheet may cause fire or damage to the module.

4. Do not operate or install in a hostile environment, such as near-water areas—bathrooms, laundry rooms, kitchen sinks, or near fire or heat-emitting devices, or exposed to direct sunlight. Otherwise it will have undesirable consequences.

5. If some foreign matter (such as water, liquid, metal sheets or other debris) accidentally falls into the module, it must be powered off immediately. Also, do not move anything on the module as it may cause a high voltage or short circuit that could result in a fire or electric shock.

6. If the module emits smoke, odor, or abnormal noise, immediately turn off the power. Similarly, if the screen does not work after power-on or during operation, it must be powered off immediately, and do not continue to operate under the same conditions.

7. Do not plug or unplug the cable on the module while the module is working or has just been powered down. This is because the capacitor on the driver circuit still maintains a high voltage. If you need to plug it in, please wait at least one minute after the power is turned off.

8. Since the module is a glass panel, please avoid external force extrusion because the glass may be damaged. Two people need to cooperate when moving the module to avoid accidents.

9. When designing the whole machine, convection heat dissipation has been fully considered. The round hole at the top is used for heat dissipation. In order to prevent overheating, do not put a cover on it during normal operation, and do not place it in a narrow and ventilated place. Bad place.

10. Many of the PDP circuits are composed of CMOS integrated circuits, so care should be taken to prevent static electricity. Therefore, when repairing, be sure to cover the anti-static bag. Before operation, be sure to fully ground.

11. There are many connecting lines around the screen. Please be careful not to touch or scratch when repairing or moving. If these cables are damaged, the screen will not work and cannot be repaired.

12. The connectors of the screen part of the circuit board are relatively fine, so be careful when replacing them to avoid damage;

13. Be careful when transporting and handling. Vibrating vibrations may cause the glass screen to break or the drive circuit to be damaged. Therefore, it must be packed in a strong outer casing for transportation and handling.

14. Store in a controlled environment to avoid temperature and humidity exceeding the specifications. If it is to be placed for a long time, it should be covere