Analysis of Common Maintenance Methods of LED Electronic Display Screen
To judge the problem, we must first deal with the primary and then the secondary, deal with the obvious and serious problems first, and deal with the small problems later. Short circuit shall be the highest priority.1. Resistance detection method: adjust the multimeter to the resistance gear to detect the ground resistance value of a certain point of a normal circuit board, and then detect the same point of another same circuit board to test whether the resistance value is different from the normal resistance value. If it is different, the scope of the problem is determined.2. Voltage detection method, adjust the multimeter to the voltage level, detect the ground voltage at a point of the suspected circuit, and compare whether it is similar to the normal value, otherwise the range of the problem is determined.
3. Short circuit detection method: adjust the multimeter to the short circuit detection gear (some are diode voltage drop gear or resistance gear, which generally has alarm function) to detect whether there is a short circuit. If a short circuit is found, it shall be solved first so that it will not burn other devices. This method must be operated when the circuit is powered off to avoid damaging the meter.
4. Voltage drop detection method: adjust the multimeter to the diode voltage drop detection gear. Because all ICs are composed of many basic single components, they are only miniaturized. Therefore, when a current passes through a pin, there will be a voltage drop on the pin. Generally, the voltage drop on the same pin of an IC of the same model is similar. According to the voltage drop on the pin, it must be operated when the circuit is powered off. This method has some limitations. For example, if the detected device is high resistance, it can not be detected. 4 Handling steps for common problems of unit board unit board failure:
A. The whole board is not bright1. Check whether the power supply is connected to the signal line.2. Check whether the test card can identify the interface. If the red light of the test card flashes, it will not be identified. Check whether the lamp board is connected with the power supply and ground of the test card, or there is a short circuit between the signal and ground of the lamp board interface, so that the interface cannot be identified. (smart test card)
3. Detect whether 74hc245 has faulty welding or short circuit, and whether the corresponding enable (EN) signal input and output pin on 245 has faulty welding or short circuit to other lines. Note: mainly check the power supply and enable (EN) signal.B. During oblique scanning, regular interlaced lines are not lit, and the display screen overlaps1. Check whether there is broken wire, faulty welding or short circuit between a, B, C and D signal input ports and 245.
2. Check whether there is open circuit, faulty welding or short circuit between output terminals a, B, C and d corresponding to 245 and 138.3. Detect whether there is a short circuit between signals a, B, C and D or whether a signal is short circuited to ground. Note: it mainly detects ABCD line signal.C. When fully lit, one or more lines are not lit
1. Detect whether the line between 138 and 4953 is open circuit, faulty welding or short circuit.D. During line scanning, two or more lines (generally multiple of 2, regular) are lit at the same time1. Check whether there is a short circuit between signals a, B, C and D.
2. Check whether the 4953 output terminal is short circuited with other output terminals.E. Single or multiple points (irregular) do not light up when fully lit1. Find the control pin corresponding to the module and measure whether it is short circuited to the line.
2. Replace the module or single lamp.F. When fully lit, one or more columns are not lit1. Find the pin controlling this column on the module and test whether it is connected to the output of the drive IC (74HC595 / TB62726).
G. There is single point or single column highlight, or whole row highlight, and it is not controlled1. Check whether the column is short circuited to power and ground.2. Check whether the line is short circuited to the positive pole of the power supply.
3. Replace its drive IC.H. The display is confused, but the signal output to the next board is normal1. Detect whether the corresponding STB latch output terminal of 245 is connected with the latch terminal of the drive IC or whether the signal is short circuited to other lines.
1. The display is confused and the output is abnormal1. Detect whether the clock CLK latch STB signal is short circuited.2. Detect whether the clock CLK of 245 has input and output.
3. Check whether the clock signal is short circuited to other lines.Note: it mainly detects clock and latch signals.J. Display out of color
1. Detect whether the data terminal of the color of 245 has input and output.2. Detect whether the data signal of this color is short circuited to other lines.3. Check whether there is open circuit, short circuit and faulty soldering at the cascade data port between the driving IC of this color. Note: it is easy to find the problem by using the voltage detection method. Check whether the voltage of the data port is different from the normal one to determine the fault area.
K. There is a problem with the output1. 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 drive IC is connected with the data port of the output interface or short circuited.4. Whether the output signals are short circuited to each other or to the ground.
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