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Oct 11,2021| LED Knowledge
For engineers repairing LED displays, it is very important to be able to judge the problem through some of the symptoms of the LED display. This is the same as a doctor diagnosing a patient’s disease, usually looking at the patient’s symptoms, and then asking about the patient’s recent situation. Diagnosing the problem of the LED display is also based on the response of the display first, and then troubleshooting the problems one by one.
When diagnosing the LED display, the signal condition of the LED display is an important indicator for judging the LED display. We can roughly judge the general problem of the LED display from the five signals of the LED display.
Common LED display signal
1. STB latch signal: send the data in the shift register to the latch, and display the data content through the drive circuit to light up the led. But because the drive circuit is controlled by the EN enable signal, the prerequisite for its lighting must be that the enable is turned on. The latch signal also needs to be coordinated with the clock signal to display a complete image. In any case, when there is an abnormality in the latched signal, the entire board will be displayed in a disorderly manner.
2. ABCD line signal: it only exists during dynamic scanning display. ABCD is actually a binary number, A is the lowest bit. If the ABCD signal is expressed in binary, the maximum control range is 16 lines (1111), and only AB signal is required in 1/4 scanning. That's it, because the AB signal range is 4 lines (11). When the line control signal is abnormal, there will be display misalignment, highlighting or image overlap.
3. Data signal: Provide the data needed to display the image. It must be coordinated with the clock signal to transmit data to any display point. Generally, the red, green, and blue data signals are separated in the LED display. If a data signal is short-circuited to the positive or negative pole, the corresponding color will appear full or not bright. When the data signal is suspended, it corresponds to The color display situation of the camera will appear unstable, resulting in chromatic aberration, blurring of the screen and other phenomena.
4, CLK clock signal: the shift pulse provided to the shift register, each pulse will cause the data to move in or out of one bit. The data on the data port must be coordinated with the clock signal to transmit data normally, and the frequency of the data signal must be 1/2 times the frequency of the clock signal. If the frequency of the data signal is not correct, under any circumstances, the entire panel display will be messy. Therefore, when the LED display is shipped from the factory, it needs to perform an accurate correction on the CLK clock signal to ensure the data frequency and the clock frequency. Always sync.
5. EN enable signal: the entire screen brightness control signal, also used for display blanking. Just adjust its duty cycle to control the change of brightness. When the enable signal is abnormal, the entire screen will appear dark, dark or tailing, etc. This is an important method to quickly screen out LED display problems.