Analysis of the problem of pixel out of control in full-color LED display

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Pixel out of control in full-color LED display is a common problem. What is the cause of this phenomenon and how to solve it?

Pixel out of control in LED display refers to the abnormal operation of the smallest imaging unit (pixel) of the display. The ratio of the number of out-of-control pixels to the total number of pixels in the full screen is called the "whole screen pixel out of control rate".

One is blind spot, that is, blind spot, which is not lit when it needs to be lit, called blind spot;

The other is constant bright spot, which is always lit when it does not need to be lit, called constant bright spot.

Generally, the common LED display pixel composition is 2R1G1B (2 red lights, 1 green light and 1 blue light, the same as below) and 1R1G1B, and out of control is generally not the red, green and blue lights in the same pixel are all out of control at the same time, but as long as one of the lights is out of control, we think that the pixel is out of control. Therefore, it can be concluded that the main reason for the out-of-control of the pixels of the full-color LED display is the out-of-control of the LED light.

LED lamp out of control cannot be found in the routine inspection and testing of LED. Under harsh conditions such as high temperature, low temperature, and rapid temperature changes, the difference in thermal expansion coefficients of materials such as LED chips, epoxy resins, brackets, inner leads, solid crystal glue, and PPA cups causes different internal stresses.

The mechanism of LED out of control caused by electrostatic discharge is very complicated. Equipment, tools, utensils and human bodies may carry static electricity and discharge it. This static electricity ranges from hundreds of volts to tens of thousands of volts, and the discharge time is at the nanosecond level. If the blue-green tube is out of control, it is often caused by the breakdown of the LED-PN junction by electrostatic discharge.

LED display screens have a complicated production process and electrostatic discharge is hard to prevent. Therefore, electrostatic protection must be carried out throughout the entire production process.

In different occasions, the actual requirements for pixel out of control rate are different. The full-color LED display screen indicator is required to be controlled within one percent; the monochrome LED display screen indicator is required to be controlled within one tenth.

At present, there is no good solution for the pixels of full-color LED display screens. It is recommended to contact the service manufacturer to return the screen to the factory for repair. If the repair cost is too high, you can consider replacing the problematic module unit board.

At present, domestic LED display screens will undergo aging tests before leaving the factory, and the LED lights of out-of-control pixels will be repaired and replaced. It is no problem to control the "whole screen pixel out-of-control rate" within 1/104 and the "regional pixel out-of-control rate" within 3/104. Some manufacturers' corporate standards even require that out-of-control pixels are not allowed before leaving the factory, but this will inevitably increase the manufacturer's manufacturing and maintenance costs and extend the delivery time.

In different application scenarios, the actual requirements for pixel out-of-control rate can vary greatly. Generally speaking, for LED display screens used for video playback, it is acceptable and achievable to control the index within 1/104; if it is used for simple character information release, it is reasonable to control the index within 12/104.