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Mar 09,2021| LED Knowledge
With the development of LED display technology, LED displays can now achieve high-definition small-pitch LED displays such as P2 and P1.875. Visually, in the next few years, LED displays will enter the family and become as common as TVs and mobile phones. The items are also very possible.
The LED display is formed by splicing multiple LED modules, and one LED module contains countless LED lamp beads. As long as the quantity of any item becomes huge, it is unavoidable that there will always be one-thousandth, or one-ten thousandth, of faults that need to be dealt with. Here is an explanation of how to repair some minor faults of the LED display. Collect it, maybe you will use it anytime!
Failure analysis of LED display problems in LED display repair
The most direct and effective method of fault analysis for beginners is the elimination method. Here we need to know a basic one. In addition to the lamp beads in the LED module, the LED display also needs to rely on three other hardware. They are respectively Yes: control card, unit board, switching power supply.
First of all: Judge whether the control card is good. First, turn on the power and check whether the indicator light of the control card is on. If it is not on, check whether there is a 5V power supply and whether the display can display the content. If the content can be displayed, it means that the function of the control card to display the content is good; Then you use the control card software to find the control card. If you can find it, it means that the function of the control card’s sending content is normal. If you can’t find it, first check whether the communication line is connected. If it is connected, then there may be a problem with the card.
Summary: If the indicator light of the control card is on normally, the software of the control card can find the control card, and there is no problem with the line connection, it means that the control card is good, otherwise, you need to replace the control card.
Secondly; check whether the power supply is normal. If the power supply is broken, it will directly cause several boards in the link to be off or abnormal or flicker abnormally. Under normal circumstances, a power supply can control 4-8 boards. If the adjacent 4-8 boards are abnormal, then it should be considered that the power supply may be abnormal. If the power supply is abnormal, you can measure whether the output voltage is between 4.9V and 5.5V through the DC voltage file of the multimeter. If so, replace the power supply.
Summary: When there are problems with several adjacent boards, the priority is to find out whether the power supply is abnormal.
Finally: we have to judge whether the unit board is good or not. The display screen signal is transmitted from the output pin of one unit board to the input signal of another board. Therefore, a problem with one board will cause the whole row behind it to be dark or abnormal. , So when there is a problem with a row of display screens, we should replace the abnormal board in this row, or jump over this board with a long cable, and then see if the backboard appears normal.
Summary: When performing screen inspection on horizontal or vertical rows, if the entire row is abnormal or the signal input is abnormal at a certain position, then there may be a problem with the unit board.
Failure analysis of LED unit board in the repair of an LED display screen
A. Problem with output
1. Check whether the line from the output interface to the signal output IC is connected or short-circuited.
2. Detect whether the cascade output data port between the final drive IC is connected with the data port of the output interface or whether it is short-circuited.
3. Check whether the clock latch signal of the output port is normal.
4. Whether the output signals are short-circuited to each other or short-circuited to the ground.
5. Check whether the output cable is good.
B. The whole board is not bright
1. Check whether the power supply is connected to the signal line.
2. Check whether 74HC245 is short-circuited with solder and whether the corresponding enables (EN) signal input and output pin on 245 is soldered or short-circuited to other circuits.
3. Check whether the test card can identify the interface. If the red light of the test card is flashing, it is not recognized. Check whether the light board and the test card have the same power ground, or the light board interface has a signal and ground short circuit, which makes the interface unrecognizable. (Smart Quiz Card)
Note: Mainly check the power and enable (EN) signal.
C. One or several lines are not bright when it is all on
Detect whether the circuit between 138 and 4953 is open, soldered, or short-circuited.
D. When the dots are scanned obliquely, the regular interlaced lines are not bright and the screen is overlapped.
1. Check whether there is any disconnection, virtual welding, or short circuit between the signal input ports A, B, C, D and 245.
2. Check whether the A, B, C, D output terminals corresponding to 245 are open circuit, virtual welding, or short circuit between the output terminals 138.
3. Check whether the signals A, B, C, and D are short-circuited or a signal is short-circuited to the ground.
Note: Mainly detect ABCD line signals.
E. The display is chaotic, but the signal output to the next board is normal
Detect whether the STB latch output terminal corresponding to 245 is connected to the latch terminal of the driver IC or the signal is short-circuited to other lines.