Liquid crystal displays are becoming more and more popular with users. Several major display manufacturers in the world have also turned their strategic attention to liquid crystal displays. However, like CRT displays, the failure rate of liquid crystal displays still exists. Many users do not understand the internal structure of the LCD monitor, and can only turn to the after-sales service company when a problem occurs. If the warranty period has expired, they will have to pay a considerable maintenance fee. The following article is a more classic fault in LCD monitors. I hope that in addition to solving this type of fault, it can also popularize the internal structure of LCD monitors.
The TCL ML-56 liquid crystal display is a flat-panel display that was introduced to the market by TCL in 2001. Its performance is not bad, but there is a common problem with this type of display, that is, when it is used for about a year, there will be no image display when it is turned on. Or the monitor suddenly goes black when it is in use, and occasionally the image comes out again after a few minutes. The performance of the fault is irregular and very annoying. During my repair process, I have encountered more than a dozen of the same failures. If this type of failure is repaired at a repair station, it will cost at least 300 yuan. If you read the following, you will feel that this problem is too simple and you can handle it yourself. Originally, this problem was also very small, and it could be fixed without spending a penny. If you don’t have tools, you just need to spend some money on tools.
The working principle of the liquid crystal display: the liquid crystal itself does not emit light, and the display and brightness adjustment of its image depend on the adjustment of the brightness of the backlight. When the liquid crystal display is working, the light emitted by the backlight passes through the liquid crystal screen to reflect the image content displayed on the liquid crystal screen into the eyes of people. Only then can we see the text and images displayed on the liquid crystal display. If the backlight is damaged, there will be no light, and we can see nothing at this time. However, if we carefully observe the LCD screen, we will see a faint image display on the LCD screen, which means that the backlight related circuit is broken.
If the backlight circuit is intact, but there is a problem with the display circuit, we will see a bright white light behind the LCD screen. Most of the failures of the liquid crystal display are backlight circuit problems or power supply problems. The most likely cause of the backlight circuit failure is the internal short circuit or open circuit of the boost coil.
Tool configuration: ￠4*200 screwdriver, 20W electric soldering iron, a piece of solder wire, and a knife (these are very easy to find and also very cheap tools).
The whole maintenance process:
1. First power on the LCD display separately, observe the failure phenomenon, whether there is the above failure performance. Then connect the signal line with the host, turn on the display, and observe whether the power indicator of the display is always green and whether there is an image on the LCD screen. If you identify it carefully, will you find a faint image appears, but there is no backlight.
2. Clean the desktop, use a soft cloth to pad the desktop, and buckle the LCD screen of the monitor down on the desktop. Make sure that the desktop is clean without any debris, otherwise the loss will be heavy.
3. Unscrew the screws of the two protective covers and remove the protective covers.
4. Unscrew the four fastening screws and remove the bracket.
5. As shown in the figure below, unscrew the fixing screws on the four corners of the back cover of the monitor.
When removing the back cover, pay attention to the position of the two left and right channel audio input lotus plugs marked with red arrows in the figure below. You need to pull it down and then lift the back cover to remove it normally.
The picture below shows the internal structure of the LCD with the back cover opened. I believe everyone would like to see what the inside of the LCD looks like.
6. Unscrew the two fixing screws on the bottom of the shielding cover, slide the shielding cover down, and then lift the shielding cover up to remove it.
7. The internal structure of the liquid crystal display consists of four circuit boards, the main board, the audio processing board, the backlight high voltage board, and the button control board. Before disassembling, touch the water pipe or other grounding devices with your hands to prevent the static electricity on your body from damaging the LCD.
8. The picture below is the high-voltage board of the liquid crystal display, which is used to generate the 2000V high voltage required by the backlight tube of the liquid crystal display. The black square is the so-called high-voltage coil. Generally, the wire diameter of the high-voltage coil is very thin and works at high voltage. Under the environment, its failure rate is the highest, and its accessories are also the most difficult to buy.
9. Use a knife to gently scrape off the insulating paint layer on the two pins of the inductor L1 until the red copper layer is exposed. The larger the exposed area, the stronger and more reliable the soldering.
10. After the electric soldering iron is heated, hold the solder wire in one hand and the soldering iron in the other, and solder the two leads of the inductor firmly.
11. Install the display in the reverse order of disassembly. Note: The position of the screw must not be installed wrong.
12. Power on and test the machine. Power on the monitor alone, after two or three seconds, the monitor will display an image indicating that the signal line is not connected.
13. Connect the signal line of the display to the host, turn on the display to check the working condition of the display and whether the image display is normal
So far, we can easily solve the problem of the black screen of the LCD! Don’t think that the LCD monitor is noble, we dare not touch it. As long as we are bold, careful and serious, we can’t do it without our DIYer!
During the maintenance process, you must be careful and conscientious. For each screw in the disassembly process, you must remember its installation position on the paper to avoid mistakes.
Post time: Jan-12-2021