Twelve steps to solve failures of LED display

1. The whole board is not bright: the board is not connected to the power supply; the input cable is reversed; the input and output are reversed; the positive and negative poles of the power supply are reversed.

2. The board is not bright and the transmission is normal: the protection circuit damage solution can short circuit the 4th and 5th pins of 74HC138.

3. One line is not bright after every three lines: 4953 is damaged (one of them is damaged).

4. One line after another line: A signal problem, please check whether 74HC245 and 74HC138 have virtual welding; you can use a multimeter to measure whether the voltage of pin 1 of 74HC138 is equal to about 2.5V, if there is a replacement 74HC138; carefully measure the path of the gold needle with ICA signal Happening.

5. Bright two lines every two lines: B signal problem, please check whether 74HC245 and 74HC138 have virtual welding; you can use a multimeter to measure whether the voltage of pin 2 of 74HC138 is equal to about 2.5V, if there is replacement of 74HC138; carefully measure the gold needle with ICA signal Access situation.

6. The upper half board is normal. The lower half board is all bright or not bright: if this is the case with the T08A interface, this should check whether the DR data signal of the next 8 lines is in the path. If it is normal, replace 74HC245 first. If it is not good, then replace the first one. 74HC595.

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

8. If one of the lights on the board is not on: check if it is not soldered and replace this tube.

9. There are four lamps that are not standing upright: first check 74HC595 for virtual welding; second replace 74HC595; third replace lamp.

10. Among the 4 vertical lamps, 3 are not bright and 1 is normal: replace the normal one.

11. If the board displays abnormality from the middle or another position: check the data signal path; replace the 74HC595 of the last normal display control lamp; if it does not exclude the replacement of the first 74HC595 of the abnormal light control. Each 74HC595 controls 8 points wide **4 points high lamps. The 74HC595 is connected in series with the DR data signal, that is, the DR signal is connected from the 14th pin to the 9th pin of the 74HC595 to the next piece of the 74HC595 to the last 74HC595. For example, the DR data of this board is from the gold pin to 74HC345 After zooming in, it will go from UR1 to UR2 to UR3 to UR8 to the output gold pin.

12. Sometimes during the process of debugging the entire screen, the modules from the front to the rear are displayed abnormally. The general fault is that the cable is not plugged in or damaged; you can also use a slightly longer cable to check the module below. Plug the cable into the abnormal module above, and see how it shows. You can also connect the output of the normal module in front of the abnormal place to the next row of modules to see how it shows.