12 steps to solve common faults of display unit board

65 views admin 2025-02-12

We often encounter faults of LED display unit board, so how to solve the faults encountered? Next, I will teach you 12 steps to solve common faults of display unit board. As follows:

1. The whole LED display board does not light up: the board is not connected to the power supply; the input cable is plugged in reverse; the input and output are reversed; the positive and negative poles of the power supply are connected in reverse.

2. The LED display board does not light up and the transmission is normal: the protection circuit is damaged. The solution is to short-circuit the 4th and 5th pins of 74HC138.

3. The LED display screen does not light up every three lines: 4953 is damaged (one of them is damaged).

4. The LED display screen lights up every other line: A signal problem, please check whether there is a cold solder joint between 74HC245 and 74HC138; you can use a multimeter to measure whether the voltage of the 1st pin of 74HC138 is equal to about 2.5V, if there is, replace 74HC138; carefully measure the path of the gold needle with ICA signal.

5. The LED display screen lights up two lines every other two lines: B signal problem, please check whether there is a cold solder joint between 74HC245 and 74HC138; you can use a multimeter to measure whether the voltage of the second foot of 74HC138 is equal to about 2.5V, if there is, replace 74HC138; carefully measure the path of the gold pin with ICA signal.

6. The upper half of the LED display screen is normal and the lower half is all lit or not: If the T08A interface has this situation, you should check whether the DR data signal of the next 8 lines is connected. If it is normal, replace 74HC245 first. If not, replace the first 74HC595.

7. The STB and CLK signals of the upper and lower halves of this board are common, and the data is separated (if it is a T12 interface, the data is also 1). If you check the T08A board, the upper and lower halves should be checked separately.

8. If one light on the board is not lit: check whether it is cold soldered and replace this lamp. 9. If 4 lights on the vertical LED display screen are not lit: first check if the 74HC595 has a cold solder joint; second replace the 74HC595; third replace the lamp. 10. If 3 of the 4 lights on the vertical LED display screen are not lit and 1 is normal: replace the normal lamp. 11. If the board displays abnormally from the middle or other positions: check the data signal path; replace the last 74HC595 that controls the normal display lamp; if the problem is not eliminated, replace the 74HC595 that controls the first abnormal lamp. Each 74HC595 controls 8 dots wide * 4 dots high lamps. 74HC595 is connected in series with DR data signal, that is, DR signal enters from the 14th pin of 74HC595 to the 9th pin and connects to the 14th pin of the next 74HC595 to the last 74HC595. For example, the DR data of this board is amplified from the gold pin to 74HC345, then to UR1, UR2, UR3, UR8 and then to the output gold pin.

9. If 4 lights on the vertical LED display screen are not lit: first check if the 74HC595 has a cold solder joint; second replace the 74HC595; third replace the lamp.

10. If 3 of the 4 lights on the vertical LED display screen are not lit and 1 is normal: replace the normal lamp.

11. If the board does not display normally from the middle or other positions: check the data signal path; replace the last 74HC595 that controls the normal display lamp; if it is not ruled out, replace the 74HC595 that controls the first abnormal lamp. Each 74HC595 controls 8 dots wide * 4 dots high lamps. 74HC595 is connected in series with DR data signal, that is, DR signal enters from the 14th pin of 74HC595 to the 9th pin and then connects to the 14th pin of the next 74HC595 to the last 74HC595. For example, the DR data of this board is amplified from the gold pin to 74HC345, then to UR1, UR2, UR3, UR8 and then to the output gold pin.

12. Sometimes, when debugging the whole screen, the display of the front module to the rear module is abnormal. Generally, the fault is that the cable is not plugged in or damaged. You can also use a slightly longer cable to plug the cable of the module under inspection to the abnormal module above to see how it displays. You can also connect the output of the normal module in front of the abnormal place above to the next row of modules to see how it displays and see which module has a problem.