LCD screen maintenance is a relatively new industry because there are few people and information available. Let me summarize my experience.
When a faulty machine comes, do not directly repair the screen. You must first make a good judgment to determine if it is a screen problem. I have misjudged it many times before, and if it was not a screen problem, dismantling the screen for repair would result in the machine being scrapped.
I will start chatting with everyone in my leisure time today about LCD screen maintenance, which is not very precise but practical.
There are several types of malfunctions that LCD screens can cause: white screen, blurred screen, black screen, dark screen, yellowing, white spots, bright lines, bright bands, dark lines, dark bands, scratches on the outer film, etc. Among these faults, the ones that are relatively easy to repair are screen dullness, yellowing, white spots, and scratches on the outer membrane.
White, blurred, and black screens are mostly caused by circuit faults. Firstly, the breakage of the screen cable should be ruled out. Then, check whether 3.3V (or 5V or 12V, early 18V) has been added to the screen. Then, sequentially check whether there is high voltage and negative pressure output in the subsequent stage, and whether the main control chip has output. A considerable portion of the screen distortion is caused by the line driver not working, which can be solved simply by flying a few wires. A small portion of the screen distortion is due to damage to the first driver module of the row or column, while there are also some screen distortion caused by changes in screen parameters, which can be adjusted by entering the bus. The most difficult and costly task is to repair the screen cable. The causes of these faults are mostly due to the corresponding driver modules being poorly soldered or damaged. It is well known that some driver modules are used to connect the screen glass and PCB board. The module is connected to both the PCB board and the glass with extremely thin solder joints. This type of solder joint cannot be distinguished with the naked eye, nor can it be welded with a soldering iron or an air gun. It needs to be matched under a high-power magnifying glass and subjected to hot pressing using specialized equipment. Some auxiliary materials used during this period, such as ACF adhesive and ACF cleaning solution, are very expensive, and the cleanliness of the operating environment directly affects the success rate of repair. The machine factor and human experience factor each account for about 50% of this operation.
The screen darkening is actually due to the aging of the LED light tube (strip), just replace it directly. Yellowing and white spots are both issues with the backlight, which can be solved by replacing the corresponding backlight film or light guide plate. Scratches on the outer membrane refer to damage to the polarizing film on the surface of liquid crystal glass, which can be easily replaced manually. Of course, there are also many precautions to be taken when implementing these faults that can be solved through replacement. When replacing the lamp tube, attention should be paid to its proper installation to avoid light leakage; When dealing with backlight, pay attention to dust prevention, otherwise you will see dust spots when the screen is lit up; When replacing the polarizing film, it is important to avoid damaging the screen when tearing off the film, and dust is a major taboo. Once dust enters during film coating, bubbles will be generated, and a film should be scrapped and restarted.