LED screen fault analysis the most direct and effective method is elimination, the display is mainly composed of three hardware: control card, unit board, switching power supply.
First of all: we judge whether the control card is good, you first look to turn on the power, whether the control card indicator light is lit, if not look to check whether there is 5V power supply, the display screen is able to display the content, as long as the content can be displayed, indicating that the control card display content function 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 to send content is good, if you can't find it, you see if the communication line is 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 it is necessary to replace the control card.
Second; We have to judge whether the power supply is good, if the power supply is bad, it will directly cause several boards at the same time is not bright or abnormal, because a power supply is controlled by several boards at the same time, that is, if your display is in the same small area of several boards do not display or display is abnormal, you should consider whether the power supply is bad, The most direct detection method is to take a multimeter to measure whether the output voltage is between 4.9 and 5.5V. If yes, replace the power supply.
And finally: We have to judge whether the unit board is good, LED full-color display signal is from the output row of one unit board to the input signal of another board, so a board problem, will cause the whole row behind it is not bright or abnormal, so when the display row has a problem, we should replace the abnormal board in this row, or use a long row of lines to jump the board over. Then see if the back board is displayed normally.
Unit board fault analysis
First, there is a problem with output
1, detect whether the output interface to the signal output IC line is connected or short-circuited.
2. Check whether the clock latch signal of the output outlet is normal.
3. Detect whether the cascade output data port between the last driver IC is connected to the data port of the output interface or whether there is a short circuit.
4. Whether the output signal is short-circuited or short-circuited to the ground.
5. Check whether the output wiring is good.
Two, fully lit when one or several lines are not lit
Detect whether the line between 138 and 4953 is open or weld or short circuit.
Three, the whole board is not bright
1. Check whether the power supply is connected to the signal cable.
2, check whether the test card to identify the interface, the test card red light flashing is not recognized, check whether the light board and the test card with the power supply, or the light board interface has a signal and ground short circuit resulting in failure to identify the interface. (Smart Test card)
3. Detect whether 74HC245 has virtual welding short circuit, and whether the input and output pins of the corresponding enable (EN) signal on 245 are virtual welding or short circuit to other lines.
Note: Mainly check the power supply and enable (EN) signal.
Fourth, in the point oblique scanning, regular interlacing does not light up the picture overlap
1, check A, B, C, D signal input port to 245 whether there is a broken line or virtual welding, short circuit.
2. Test whether the output terminals A, B, C, D corresponding to 245 and 138 are open or welded or short-circuited.
3, detect A, B, C, D signals between the short circuit or a signal and the ground short circuit.
Note: Mainly detect ABCD line signal.
The display is chaotic, but the signal output to the next board is normal
Detect whether the STB latch output corresponding to 245 is connected to the latch of the driver IC or the signal is short-circuited to other lines.
One or more columns are not bright at all
Locate the pin that controls the column on the module and test whether it is connected to the output of the driver IC (74HC595/TB62726,,,,).
There is a single point or single column highlighting, or the whole row highlighting, and is not controlled
1. Check whether the column is short-circuited with the power supply.
2. Detect whether the line is short-circuited with the positive terminal of the power supply.
3. Replace its driver IC.
Eight, the display is chaotic, the output is abnormal
1. Detect whether the clock CLK latch STB signal is short circuit.
2. Check whether the clock CLK of 245 has input and output.
3. Detect whether the clock signal is short-circuited to other lines.
Note: Mainly detect clock and latch signals.
Nine, display lack of color
1. Check whether the data end of the color of 245 has input and output.
2. Detect whether the data signal of the color is short-circuited to other lines.
3, detect whether the cascade data port between the color of the driver IC is open or short circuit, virtual welding.
Note: The voltage detection method can be used to find the problem more easily, detect whether the voltage of the data port is different from the normal one, and determine the fault area.
Ten, there is a single point or more points (irregular) not bright
1. Find the corresponding control foot of the module to measure whether it is short-circuited with the bank.
2. Replace the module or single lamp.
In line scanning, two or more lines (generally a multiple of 2, regularly) are lit at the same time
1, detect A, B, C, D signals between the short circuit.
2. Detect whether the 4953 output terminal is short-circuited with other output terminals.
None of the leds are bright
The main power supply is not turned on; Part of the LED is not on: the polarity of the switching power output connection is reversed or the module connection is open.
13. All leds are dim
The number of loaded leds is too large or the polarity of the module is reversed; Some LED dim and lamp beads hot: module wiring short circuit; Inconsistent LED brightness: too many loaded leds.
14, LED flashing
Poor line contact; Burning safety: There is a short circuit in the module or wiring.