LCD screens may have some problems during long-term use, such as white screen, flowery screen, black screen, dark screen, yellowing, white spots, bright lines, bright bands, dark lines, dark bands, outer film scratches, etc. What should I do?

When the LCD screen has the above faults, how should we troubleshoot and solve the problem? Today we has sorted out 2 common faults and solutions for LCD screens for you, so save them quickly!

A: LCD screen white screen fault

1. First, determine whether the fault is in the switching power supply, signal processing part, or TCON part.
2. The fault range can be determined by measuring the LVDS signal connecting the signal processing part and the TCON part. If it is normal, the TCON part at the back end is suspected; if it is abnormal, check the signal processing part at the front.
3. For the TCON part inspection, the main checks are: key point voltage and RSDS line connectivity.
4. There are two situations for white screen:

a) There is signal input, the whole screen is white, and the image is not clear. This is caused by a fault in the control circuit board;
c) There is signal input, the whole screen is white, and the image can be seen, but the image seems to be covered by a layer of fog. This is caused by a bad cell. It cannot be repaired and the LCD screen needs to be replaced.

5. Check three voltages:

a) 10V (or 12V), which is a voltage generated by a simple boost of the 5V (or 3.3V) screen power supply voltage.
b) 25V (or 30V), which is output by the DC---DC circuit.
c) Negative 7 volts, which is also output by the DC---DC circuit. If these three voltages are normal, then consider whether the main chip is poorly soldered or damaged. Another key point to check is the screen cable, to see if the screen cable is installed in place and whether it has good contact. If necessary, clean the screen cable. In addition, the first thing to check for the DC---DC conversion circuit of the screen is the filter capacitor, and the second is that the IC of the DC--DC circuit is often broken.

6. Characters are blurred or tailed: Check the VGA signal line, and focus on whether the ground wire of the R.G.B three-color line is connected normally → Replace the screen line or adapter board → Rewrite the driver → Change the driver board → LCD screen backplane signal interface IC is broken → LCD screen backplane contrast potentiometer adjustment → LCD screen light guide plate is misaligned → - Polarizer is wrong.

7. The screen displays an error prompt "out of frequency range": Check the signal line → Rewrite the MCU driver → Replace the EPROM → Rewrite the EPROM program → Change the driver board.

8. After power on, the white screen appears backlight without pressing the switch button: After pressing the button, the image can be displayed normally, which is caused by the reverse connection of the switch signal and ADJ signal of the high-voltage board interface. Some of the switch signal outputs of the driver board MCU are abnormal, which can be rewritten The program can be repaired or the MCU can be replaced.

B: LCD screen black screen failure

It may be a bad built-in power supply or a bad driver board inside the machine.

Troubleshooting method: Check whether the power output is normal. If there is no output, it can be confirmed that the power supply is bad. If the power output is normal, it may be that the driver board is bad.

1. The LCD screen panel black screen failure is first caused by abnormal power supply circuit:

First check whether the 12V and 5V voltages are normal. If the 5V voltage is abnormal, it may be caused by the input level of the power supply circuit or the increased load.

After troubleshooting and replacing the faulty components, the 5V voltage may return to normal, but it may still not be able to boot up. This may be related to the MCU program or its own damage. If you cannot find the original replacement board, you can consider purchasing a replacement board.
2. The second situation is that the power supply is normal, the key response of the panel is also normal, and the screen is black:

The power supply is normal, the key response is normal, but the screen is black. It may be that the backlight is not lit, and there is a problem with the driver backlight circuit. It is necessary to connect the host to turn on the machine for inspection. If the image is dim, the signal processing circuit is normal, and the problem is in the high-voltage board and the control switch circuit. High-voltage board failures may include fuse burnout, switch chip failure, etc. Damage to the backlight tube may also cause a black screen, but the manifestation is different.

The above summarizes the LCD screen white screen and black screen failures and treatment methods. The solutions provided in the article are for reference only. Please operate with caution according to the specific situation. When it comes to display hardware failure, please be sure to seek help from professional maintenance personnel.