How do you repair the LED display failure
date：2019-12-31
LED display failure and inspection and maintenance
1. There is a light, dark light and no light on the unit board.
Inspection and maintenance:
(1) Visually check whether the lead out pin of the line pipe on the unit board is improperly welded; if so, weld the pin.
(2) Use a multimeter to measure whether the output end of the line pipe is connected with the module pin. If not, use a data line to connect it. If it is connected, measure whether it is short circuited with the ground. If not, measure whether the voltage is normal (multimeter measurement method: connect the black probe with GND and the red probe to measure the voltage of each pin); if yes, judge whether the output end of the line pipe is open to the corresponding module pin; if not, measure the output end of the line pipe Whether the input end is normal; if yes, the line pipe is broken and replaced with the same type of line pipe; if no, measure whether the output end of corresponding hc138 is normal; if yes, judge whether the output end of hc138 is open circuit with the input end of line pipe; if no, judge whether hc138h is bad.
(3) If all the above measurements are normal, there is a quality problem in the line pipe itself, and the line pipe of the same model shall be replaced.
2. A column of long bright, dark bright or not appears on the unit board.
Inspection and maintenance:
(1) Visually check the module pin and integrated circuit corresponding to the fault on the unit board for faulty soldering, short circuit and open circuit; if so, weld the pin.
(2) Use a multimeter to measure the output terminal of hc595 [output pins of hc595: 1, 2, 3, 4, 5, 6, 7, 15, eight columns of control terminals in total; when measuring, the response area dividend, green integrated circuit, sequence: whether the red and green (R, g) voltage is normal; if so, judge whether the output terminal of hc595 is open circuit with the input terminal of the module; if not, judge whether the hc595 is broken, and replace it with the hc595 integrated circuit of the same model (when replacing the integrated circuit hc595, pay attention not to disconnect the circuit lead). If the hc595 is normal, then judge whether the module is broken and replace it with a module of the same model
3. The cell board has eight lines, columns or single points of no light, long light, dark light and 16 points.
Inspection and maintenance:
(1) Visually check the module pins and leads corresponding to the fault for short circuit, faulty welding and open circuit.
(2) Whether the common connecting lines between the upper and lower modules and between the left and right modules of each cell (the unit board is divided into the upper and lower cells in total) are normal (set the multimeter to the adjacent end, measure the line input end of the module and the lead connection of each control input end). If yes, it is judged that the module is bad. If no, it can be eliminated by directly replacing the connection with the fine data line.
(3) A multimeter can be used to directly measure whether a single module is normal. If so, it is judged as the internal short circuit between the circuit board and the module. If not, it is judged as the module is broken, and the module of the same model shall be replaced.
4. There are several lines of cell board or the whole cell (the cell board is divided into upper and lower cells) that are not bright, long bright and dark bright.
Inspection and maintenance:
(1) Visually check whether the corresponding line pipe, through inductance and integrated circuit are faulty welding, short circuit and open circuit. If so, disconnect the short circuit and re weld the faulty welding and open circuit.
(2) Use a multimeter to measure whether the output voltage of each line pipe is normal (multimeter measurement method: connect the black probe with GND and red probe to measure the voltage of each pin); if yes, judge whether the output terminal of the line pipe is open to the corresponding module pin; if no, measure whether the input terminal of the line pipe is normal; if yes, the line pipe is broken and replaced with the same model line pipe; if no, measure the corresponding hc138 Whether the output terminal of hc138 is normal; if so, judge whether the output terminal of hc138 is open to the input terminal of the line pipe; if not, judge whether hc138 is bad.
(3) Replace the 16p cable with a good one. Measure the voltage of pins 1, 2 and 3 of the hc138 address input, the gate 4, 5 (low level is valid), 6 (high level is valid) and whether the power supply of the integrated circuit is normal. If so, judge that hc138 is bad, and then continue to check with (2). (4) Whether the 5V connecting line between the two cells is disconnected? If so, it can be directly connected with the same power line (generally, the whole cell is not bright or dark).
(4) Measure whether the line signal at the input end of the unit board (16p can be regarded as 12 groups of which 2, 4, 6 and 8 pins are a, B, C and D respectively) has internal short circuit, open circuit and whether the drive is normal after inputting hc245. If so, measure whether the signal inputted to hc138 via hc245 drive is normal, and then continue to check with (2). If not, it is judged that hc245 is bad, and replace it with the integrated circuit of the same model.
5. The whole screen of the unit board is not bright or dark.
Inspection and maintenance:
(1) Visually check whether the power connection cable, 16p cable between unit boards and power module indicator 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) Measure the low voltage of the power module, adjust the fine adjustment (the fine adjustment of the power module near the indicator light) to make the voltage reach the standard.
6. There are no red or green cells in the cell board (the cell board is divided into upper and lower cells).
Inspection and maintenance:
(1) Visually check whether the integrated circuit and 16p cable corresponding to the fault have faulty welding, open circuit and whether the 5V power supply is normal (it can be directly replaced by a good 16p cable).
(2) The 16p connecting line between the unit boards (the 9 and 11 pins of the 16p line are red signals, and the 10 and 12 pins are green signals) and the output of the front unit board (judgment method: if a long 16p line is connected in a normal way, then it is judged that there is a problem behind it; otherwise, there is a problem in the front). If so, measure the input to the hc245 red signal, and drive it to the 1 of hc595 Check whether the 4-pin is normal (if yes, and other pins of hc595 are normal, judge whether hc595 is broken, and replace it with integrated circuit of the same model). If not, check whether 16p cable has problems and input
