Failure analysis and treatment of LED display problems:
Fault analysis is the most direct and effective method for beginners to eliminate. The display is mainly composed of three major hardware: control card, unit board, and switching power supply.
First of all: we judge whether the control card is good, you first look at turning on the power, whether the control card indicator is on, if it is not on, check whether there is 5V power supply, whether the display can display content, as long as it can display content , Indicating that the display function of the control card is good; then you can use the control card software to find the control card. If you can find it, the function of sending content of the control card is good. If you cannot find it, look at the communication line. Connected, if it is connected, there may be a problem with the card. As long as these two functions are good, the control card is good, otherwise the control card will be replaced.
Secondly; we have to judge whether the power supply is good. If the power supply is broken, it will directly cause several boards to be off or abnormal at the same time, because a power supply controls several boards at the same time, that is, if your display screen is Several boards in the same small area are not displayed or displayed abnormally. You should consider whether the power supply is broken. The most direct detection method is to take a multimeter ground DC voltage and measure whether the output voltage is between 4.9 ~ 5.5V. If it is necessary to replace the power supply.
Finally: we have to judge whether the unit board is good, the display signal is transmitted from the output pin of one unit board to the input signal of another board, so a problem with one board will cause the entire row behind it to be not bright or abnormal , So when there is a problem with a row of the display screen, we should replace the board with an abnormal start in this row, or jump over this board with a long row of cables, and then see if the board behind it shows normal.
Unit board failure analysis
A. There is a problem with the output
1. Check whether the line from the output interface to the signal output IC is connected or short-circuited.
2. Check whether the clock latch signal of the output port is normal.
3. Check whether the cascade output data port between the last driver IC is connected to the data port of the output interface or whether it is short-circuited.
4. Whether the output signals are shorted to each other or shorted to ground.
5. Check whether the output cable is good.
B. One line or several lines are not bright when it is all bright
1. Check whether the line between 138 and 4953 is open or virtual welding or short circuit.
C. The whole board is not bright
1. Check whether the power supply is connected to the signal line.
2. Check whether the test card is to identify the interface. If the test card flashes red, it is not recognized. Check whether the light board and the test card are on the same power ground, or the light board interface has a signal and ground short circuit that cannot identify the interface. (Smart Test Card)
3. Check whether the 74HC245 has a short circuit of virtual soldering, and whether the corresponding enable (EN) signal input and output pin on 245 is virtual soldering or short circuited to other lines.
Note: Mainly check the power and enable (EN) signal.
D. During dot-and-slope scanning, regular interlaced display screens overlap
1. Check whether there is a broken wire, virtual welding or short circuit between the A, B, C and D signal input ports to 245.
2. Check whether the output terminals A, B, C, and D corresponding to 245 are disconnected or virtual welded or short-circuited.
3. Detect whether there is a short circuit between A, B, C and D signals or a signal is shorted to ground.
Note: Mainly detect ABCD line signal.
E. The display is chaotic, but the signal output to the next board is normal
1. 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.
F. When one column is full, one or several columns are not lit
1. Find the pin that controls the column on the module, and test whether it is connected to the output terminal of the driver IC (74HC595 / TB62726 ,,,).
G. There is single-point or single-column highlighting, or entire row highlighting, and it is not controlled
1. Check whether the column is short-circuited to the power ground.
2. Check whether the line is short-circuited with the positive pole of the power supply.
3. Replace its driver IC.
H. The display is chaotic and the output is abnormal
1. Check whether the clock CLK latch STB signal is short-circuited.
2. Check whether the 245 clock CLK has input and output.
3. Check whether the clock signal is short-circuited to other lines.
Note: Mainly detect clock and latch signal.
I. Display lack of color
1. Detect whether there is input or output of the data terminal of the color of 245.
2. Check whether the data signal of this color is short-circuited to other lines.
3. Check whether the cascade data ports between the driver ICs of this color have open circuit or short circuit or virtual soldering.
Note: It is easier to find the problem by using the voltage detection method, detect whether the voltage of the data port is different from the normal one, and determine the fault area.
J. There is a single point or multiple points (irregular) when the light is full
1. Find whether the control pin corresponding to the module measures short circuit with the bank.
2. Replace the module or single lamp.
K. During line scanning, two or more lines (usually a multiple of 2, regular) light up at the same time
1. Detect whether there is a short circuit between the signals of A, B, C and D.
2. Check whether the output of 4953 is short-circuited with other outputs.
L. All LEDs are off: the total power is not turned on; some LEDs are off: the polarity of the switching power supply output wiring is reversed or the module wiring is disconnected;
All LEDs are dim: too many LEDs are loaded or the polarity of the module is reversed; some LEDs are dim and the lamp beads are hot: the module wiring is shorted; the LED brightness is not
Consistent: too many load LEDs
LED flashing: poor line contact; burn insurance: short circuit in the module or wiring.
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