Causes and solutions for white shifts on TFT LCD screens

     White spots on TFT LCD screens are usually fixed white spots or areas on the screen, which do not change with the displayed content. The reasons are as follows:

A. Liquid crystal material problem

The core of the LCD screen is to display colors by controlling the light transmittance through the rotation of liquid crystal molecules. If the liquid crystal material is abnormal, it may cause the local area to fail to block light normally and appear white:

· Liquid crystal leakage: When the screen is poorly sealed (such as aging of the edge glue layer, cracking of the glass substrate caused by external impact), the liquid crystal may seep out from the broken part and gather in a certain area. The leaked liquid crystal cannot be effectively filtered by the polarizer, causing the area to continue to transmit light and form white spots.

B. Pixel/sub-pixel failure

Each pixel is composed of three sub-pixels: red (R), green (G), and blue (B), and the color is mixed by controlling the transmittance of liquid crystal. If the liquid crystal electrode or driving circuit of a sub-pixel fails, it will not be able to adjust the light transmission normally:

· Electrode short circuit/open circuit: Manufacturing defects or external forces (such as extrusion, electrostatic breakdown) may damage the electrode circuit of the sub-pixel, causing the liquid crystal molecules to be unable to respond to electrical signals and always in the "light transmission" state (white).

· Driver IC abnormality: Failure of the driver chip (responsible for sending control signals to pixels) may cause the sub-pixels in the corresponding area to fail to receive the correct switch instructions and continue to transmit light.

C. Backlight problem

· The back of the backlight is squeezed by the motherboard components, which will damage the film material and light guide plate of the backlight, causing the brightness of the squeezed position of the LCD screen to become brighter, thus forming a white shift.

· Light guide plate/diffuser defect: Uneven light guide plate or dirty diffuser may cause unbalanced light distribution, excessive brightness in local areas, and white spots (usually accompanied by uneven overall brightness of the screen).

D. Polarizer abnormality

The function of the polarizer is to filter the direction of light so that the liquid crystal can correctly control the color. If the polarizer is damaged, it may cause abnormal light transmission:

· Physical damage: The screen is squeezed, rubbed or scratched by sharp objects, which may cause the polarizer to partially fall off, wrinkle or scratch, destroying its ability to filter light and forming white spots.

· Poor bonding: The polarizer and the glass substrate are not tightly bonded (such as bubbles and dust entering), which will cause local light scattering and appear as white patches.

E. External use factors

· External impact: Falling and heavy pressure may cause the glass substrate to break and the internal structure to be misaligned (such as the liquid crystal layer and the polarizer are separated), causing local display abnormalities.

· Long-term aging: After the screen has been used for many years, the internal components (such as sealants and polarizers) have naturally aged, and the materials may become brittle and cracked, resulting in liquid crystal leakage or abnormal light transmission.

F, Solution:

· First press lightly around the white spot. If the white spot changes with pressure (expands/shrinks), it may be liquid crystal leakage or internal structure looseness. In this case, the entire LCD screen needs to be replaced.

· If the white spots are only obvious under certain colors (such as black background), it may be that the LCD cannot block light; if they exist under all colors, it may be related to the backlight or polarizer, including the back of the backlight being squeezed, the backlight material, the polarizer material and the cleanliness of the patch. This defect requires the replacement of the backlight or polarizer.

    Shenzhen Hongjia Technology has 12 years of professional research and development, production and sales of 1.14-inch to 12.1-inch LCD screens and matching touch screens, serving many Fortune 500 companies around the world, providing 36 months of after-sales service, multiple models, multiple sizes, and can be customized. Customers are welcome to email for consultation.