Common Faults and Troubleshooting of LED Display Screens

1. The whole LED display screen is not lit
① Check whether the power supply and signal line are connected;
② Check whether the test card can identify the interface. If the red light of the test card flashes, 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 short circuit between the signal and the ground, resulting in the inability to identify the interface (intelligent test card)
③ Check whether the 74HC245 has a short circuit, and whether the corresponding enable (EN) signal input and output pins on 245 are short-circuited or short-circuited to other lines
Note: Mainly check the power supply and enable (EN) signal

2. When the LED display screen is scanning at a point, the alternate lines are not lit regularly and the display screen overlaps
① Check whether there is a disconnection or a disconnection or a short circuit between the A, B, C, D signal input port and 245
② Check whether there is a disconnection or a disconnection or a short circuit between the A, B, C, D output port corresponding to 245 and 138
③ Check whether there is a short circuit between the A, B, C, D signals or a short circuit between a signal and the ground. Note: Mainly check the ABCD line signals.

3. When the LED display is fully lit, one or several rows are not lit
Check whether the line between 138 and 4953 is open or poorly soldered, or short-circuited.

4. When the LED display is scanning, two or several rows (usually multiples of 2, regularly) are lit at the same time
① Check whether there is a short circuit between the A, B, C, and D signals
② Check whether the 4953 output terminal is short-circuited with other output terminals

5. When the LED display is fully lit, one or more points (irregularly) are not lit
① Find the control pin corresponding to the module to measure whether it is short-circuited with the row
② Replace the module or single lamp

6. When the LED display is fully lit, 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,,,).

7. The LED display has a single point or a single column highlighted, or the entire row is highlighted and uncontrolled
① Check whether the column is short-circuited with the power ground.
② Check if the line is short-circuited to the positive pole of the power supply.
③ Replace its driver IC

8. The LED display screen displays confusion, but the signal output to the next board is normal
Check if 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.

9. The LED large screen displays confusion and the output is abnormal 1 Check if the clock CLK latch STB signal is short-circuited.
① Check if the clock CLK of 245 has input and output.
② Check if the clock signal is short-circuited to other lines. Note: Mainly check the clock and latch signals

10. The LED display screen displays color loss
① Check if the data terminal of the color of 245 has input and output.
② Check if the data signal of the color is short-circuited to other lines.
③ Check if the cascade data port between the driver ICs of the color is open or short-circuited, or has a cold solder joint.
Note: The voltage detection method can be used to find the problem more easily. Check whether the voltage of the data port is different from the normal one to determine the fault area.

11. There is a problem with the output of the LED display
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 short-circuited.
④ Check whether the output signals are short-circuited to each other or short-circuited to the ground.
⑤ Check whether the output wiring is good.

12. A row of LED display unit board appears long bright, dim bright, or no bright.

Repair method:
(1) Visually check whether the row tube lead pins on the unit board are poorly soldered; if so, solder the pins.
(2) Use a multimeter to measure whether the voltage at the output end of the row tube is normal (multimeter measurement method: connect the black test lead to GND and the red test lead to measure the voltage of each pin); if yes, then determine whether the row output end and the corresponding module pin are broken; if no, measure whether the input end of the row tube is normal; if yes, then the row tube is broken and replace it with a row tube of the same model; if no, measure whether the output end of the corresponding HC138 is normal; if yes, then determine whether the output end of HC138 and the input end of the row tube are broken; if no, then determine that HC138H is broken.

(3) If the above measurements are all normal, then there is a quality problem with the row tube itself and replace it with a row tube of the same model.

13. A column of long light, dim light, and no light appears on the LED display unit board.

Repair method:
(1) Visually check whether the module pins and integrated circuits corresponding to the fault on the unit board are poorly soldered, short-circuited, or broken; if yes, solder the pins.
(2) Use a multimeter to measure the output of HC595 [HC595 output pins: 1, 2, 3, 4, 5, 6, 7, 15, a total of eight columns of control terminals; when measuring, the red and green integrated circuits should be distinguished, and the order should be: whether the red and green (R, G) voltages are normal; if so, it is judged that the HC595 output terminal and the module input terminal are broken; if not, it is judged that the HC595 is broken and replaced with the same model of HC595 integrated circuit (when replacing the integrated circuit HC595, pay attention to the circuit leads not being disconnected).

14. The LED display unit board has eight rows, columns or single points that are not lit, long lit, dimly lit, and 16 points. 

Repair method:
(1) Visually check whether the module pins and leads corresponding to the fault are short-circuited, poorly soldered, or broken.
(2) Check whether the common connection line between the upper and lower, left and right modules of each cell (the cell board is divided into two cells, upper and lower) is normal (set the multimeter to the ringing end, and measure the lead connection of the module row input end and each control input end). If so, it is judged that the module is broken. If not, it can be directly replaced with a thin wire to eliminate the problem. 
(3) The multimeter can be used to directly measure whether a single module is normal. If so, it is judged that there is an internal short circuit between the circuit board and the module. If not, it is judged that the module is broken and replaced with a module of the same model.

15. On the LED display cell board, several rows or the entire cell (the cell board is divided into two cells, upper and lower) are not lit, always lit, or dimly lit. 
Repair method:
(1) Visually check whether the corresponding row tube, through-core inductor, and integrated circuit are poorly soldered, short-circuited, or open-circuited. If so, disconnect the short-circuited part and re-solder the poorly soldered or open-circuited part.
(2) Use a multimeter to measure whether the voltage at the output end of each row tube is normal (multimeter measurement method: connect the black test lead to GND and the red test lead to measure the voltage of each pin); if yes, then determine whether the row output end and the corresponding module pin are disconnected; if no, measure whether the input end of the row tube is normal; if yes, then the row tube is broken and replace it with a row tube of the same model; if no, measure whether the corresponding HC138 output end is normal; if yes, then determine whether the output end of HC138 and the input end of the row tube are disconnected; if no, then determine that HC138 is broken.

(3) Replace it with a good 16P cable and measure the voltage of the HC138 address input pins 1, 2, 3, the selection pins 4, 5 (low level valid), 6 (high level valid) and the integrated circuit power supply to see if they are normal. If yes, then determine that HC138 is broken, and then continue to check with (2). (4) Is the 5V connection line between the two cells disconnected? If so, you can directly connect it with the same power line (the general phenomenon is that the whole cell is not lit or dim). 
(4) Measure the row signal at the input end of the unit board (the gold finger 16P can be regarded as 13 groups, of which 8, 9, 10, and 11 are four groups of row signals L0, L1, L2, and L3 respectively) to see if there is an internal short circuit, a circuit break, and whether the drive is normal after inputting HC244. If so, measure whether the signal driven by HC245 and inputting HC138 is normal, and then continue to check with (2). If not, it is judged that HC245 is broken and replaced with an integrated circuit of the same model.

16. Fault phenomenon: LED display unit board, the whole screen is not lit or dim. 
Repair method:
(1) Visually check whether the power connection line, the 16P cable between the unit board and the power module indicator light are normal.
(2) Use a multimeter to measure whether the unit board has normal voltage, and then measure whether the voltage output of the power module is normal. If not, it is judged that the power module is broken.
(3) If the voltage of the power module is low, adjust the fine-tuning (fine-tuning near the indicator light of the power module) to make the voltage reach the standard.

17. Fault phenomenon: LED display unit board, there is no red or green in the small area (the unit board is divided into two small areas, upper and lower).

Repair method:
(1) Visually check whether the integrated circuit and 16P cable corresponding to the fault have cold soldering, circuit breakage, and whether the 5V power supply is normal (you can directly replace it with a good 16P cable).
(2) Check whether the 16P connecting line between the unit boards (pins 1 and 2 of the 16P cable are red signals, and pins 3 and 4 are green signals) and the output of the front unit board (judgment method: take a long 16P cable and cross-connect it. If it is normal, then measure whether the red signal input to HC245 and the 14th pin sent to HC595 after driving is normal (if it is, and the other pins of HC595 are normal, then it is judged that HC595 is broken and replaced with an integrated circuit of the same model). If not, check whether there is a problem with the 16P cable and abnormal input.

18. Fault phenomenon: The upper and lower modules in the middle of the LED display unit board are both lacking red or green, or lacking red or green from the abnormal position to the end.
Repair method:
(1) Visually check whether the integrated circuit corresponding to the fault on the unit board, such as HC595, is poorly soldered, short-circuited, or open-circuited; if so, solder the pins.
(2) Check whether the 5V power supply is normal. 
(3) Use a multimeter to measure whether the voltage of the 14th pin of the input terminal of the HC595 corresponding to the fault is normal; if so, it is judged that the HC595 is broken (when other power supplies are normal), and it is replaced with an integrated circuit of the same model; if not, check the voltage of the 9th pin output terminal corresponding to the HC595 in front, and whether the circuit connection line is disconnected. If not, it is judged that the HC595 is broken, and it is replaced with an HC595 integrated circuit of the same model (when replacing the integrated circuit HC595, pay attention to the circuit leads not being disconnected).

19. Fault phenomenon: LED display unit board has irregular phenomenon.

Repair method: (1) Visually check whether the connection wires, 16P wiring and other circuits on the unit board are normal. (2) Check whether the clock signal, 595OE terminal, latch clock and 138EN terminal signals (16P is divided into 13 signals, among which the 4th pin is the clock, the 6th pin is the 595OE terminal, the 7th pin is the latch clock and the 12th pin is the 138EN terminal) are normal. If so, there is a problem with the output terminal of the front unit board. If not, check whether the signal is driven after being sent to HC244. If not, it is judged that HC244 is broken and replaced with the same model HC244. (3) Check whether there are short circuits, open circuits, or cold solder joints at the input terminals of pins 11, 12, and 13 of HC595 and pins 4 and 5 of HC138, and whether their respective voltages are normal. If not, it is determined that the corresponding HC595 and HC138 are broken and replaced with integrated circuits of the same model.

(4) Check whether there is a short circuit at the output terminal of the unit board.

20. Fault phenomenon: The entire LED display screen, i.e., eight zones (the display screen needs to be divided into two zones if it is more than 1 meter high), has abnormal lines, for example, some lines are bright and some lines are dark.

Repair method:
(1) Visually check whether the receiving board (intuitively, it is the partition board, i.e., the board connected to the screen driver board) has cold solder joints, short circuits, open circuits, and whether the MC3486 connector is loose.
(2) Check the second MC3486 near the 5V power socket on the receiving board. You can also directly replace it with a good MC3486 (the pin arrangement of MC3486 is:
Pins 1 and 2 are input, pin 3 is output; pins 4 and 12 are power terminals; pins 6 and 7 are input terminals, pin 5 is output terminal; pins 9 and 10 are input terminals, pin 11 is output terminal; pins 14 and 15 are input terminals, pin 13 is output terminal; pins 8 and 16 are 5V power terminals). 
(3) Check whether the screen transmission line is detached or poorly soldered, and then measure whether the HC245 driver near the 5V power socket is normal. If not, it is judged that the HC245 is broken and replaced with the same model HC245.

21. Fault phenomenon: The entire screen of the LED display screen has super bright bars, no light or irregular phenomena.

Repair method:

(1) Check whether the indicator light of the system board is flashing, whether the connection line between the system boards is normal, and whether the 5V power supply of the receiving board is normal.

(2) If the above phenomenon occurs, it is generally because the first MC3486 near the 5V power socket on the receiving board is broken. It can be directly replaced with the same type of MC3486; if it is still not normal after replacing the MC3486, check whether the HC244 driver near the 5V power socket on the receiving board is normal. If not, replace it with the same type of HC244.

22. Fault phenomenon: There is no red, no green or other irregular phenomena in a certain area of ​​the LED display screen

Repair method:

(1) Visually check whether the transmission line of the system board and the MC3486 on the receiving board have fallen off, poor soldering, etc.
(2) If there is no red or green, you can directly replace it with a good MC3486 (starting from the 5V power socket, 3 to 6 MC3486, four MC3486 correspond to eight zones respectively), or you can swap the above four blocks, so that you can more quickly determine which MC3486 is broken.

(3) Find the zone corresponding to the fault, and measure whether the 26-pin output and other zones are normal (when measuring, it is best to make the pen all yellow, the measurement result is more accurate). If so, it is judged that there is a problem with the driver board and the cable. If not, measure the corresponding HC244 driver and the connection line between HC244 and other circuits to see if they are normal. If not, check according to (2).

23. Fault phenomenon: The monitoring screen freezes (the board is not well ventilated, the temperature is too high, and the board is burned)
① First ping the corresponding screen network to see if it is connected, and restart it remotely;
② If the restart is invalid, find the corresponding board and check whether the board is overheated or damaged. If it is overheated, remove it to cool it down, and return it to the factory for repair if it is burned
③ The location of the matrix is ​​dusty and does not meet the air requirements of the computer room. A large amount of dust enters the matrix, which is also the reason for the overheating temperature.

24. Fault phenomenon: The platform shows that the camera is offline (the network is not connected, the computer freezes, and the forced switch will cause the configuration file to be damaged)
① Check whether the NVR is offline in the "Equipment Operation Status Detection Platform"
② Check whether the NVR can be pinged through the ping command
③ If the network is normal, remotely go to the central server where the NVR is located to re-service
④ If it is still not online, check the network configuration file and re-configure the file
⑤ If there is a problem with the database, re-create the database.