Judging the problem must be dealt with first and lastly, and it will be treated obviously and seriously, and then dealt with small problems. The short circuit should be the highest priority.
1. Resistor detection method, adjust the multimeter to the resistance file, detect the resistance value of a certain point of a normal circuit board, and then test whether the same point of another identical circuit board is different from the normal resistance value. If it is different, the scope of the problem is determined.
2 , voltage detection method, the multimeter is adjusted to the voltage file, the ground voltage of a certain point of the circuit suspected of having a problem is detected, and the comparison is similar to the normal value, otherwise the range of the problem is determined.
3 , short-circuit detection method, the multimeter is adjusted to the short-circuit detection block (some diode voltage drop or resistance file, generally has an alarm function), to detect whether there is a short circuit phenomenon, the short-circuit should be resolved first, so that it does not burn out Other devices. This method must be operated in the event of a power failure to avoid damage to the meter.
4 , pressure drop detection method, the multimeter is adjusted to the diode voltage drop detection file, because all ICs are composed of a basic number of unit parts, only miniaturized, so when there is current on one of its pins, There will be a voltage drop across the pin. Generally , the voltage drop on the same pin of the IC of the same model is similar. According to the voltage drop value on the pin, the circuit must be powered off. This method has certain limitations. For example, if the device under test is high-resistance, it will not be detected. Fourth, the processing steps of the common problems of the unit board Unit board failure:
　 A. The whole board is not bright
1. Check if the power supply and signal cable are connected.
2. Check whether the test card is identified by the interface. If the red light of the test card flashes, it is not recognized. Check whether the light board is connected to the test card, or the signal board is shorted by the ground and the interface is unrecognizable. (smart test card)
3. Detect whether the 74HC245 has a short circuit or not, and the corresponding enable ( EN ) signal on the 245 is soldered or shorted to other lines. Note: Mainly check the power and enable ( EN ) signals.
　 B. When the oblique scan is performed, the regular interlaced display does not light up and the screen overlaps.
1. Check whether the A , B , C , D signal input port to 245 is broken or short-circuited or short-circuited.
2, corresponding to the detected 245 A, B, C, D and the output terminal 138 is open circuit or cold solder joint, the short-circuit.
3. Detect whether there is a short circuit between the signals of A , B , C , and D or a short circuit between the signal and the ground. Note: The ABCD line signal is mainly detected .
C. One or several lines are not lit when fully illuminated
1. Detect whether the line between 138 and 4953 is open circuit or short welding or short circuit.
　 D. In the line scan, two lines or a few lines (usually a multiple of 2 , regular) are lit at the same time
1. Detect whether there is a short circuit between the signals A , B , C , and D.
2. Check if the output of the 4953 is shorted to other outputs.
　 E. There is a single point or multiple points (irregular) when it is fully lit.
1. Find whether the corresponding control pin of the module is short-circuited with the line.
2. Replace the module or single lamp.
　 F. One column or several columns are not lit when fully illuminated
1. Find the pin that controls the column on the module and check if it is connected to the output of the driver IC ( 74HC595/TB62726 ).
　　 G. There is a single point or single column highlighting, or the entire line is highlighted and uncontrolled
1. Check if the column is shorted to the power ground.
2. Check if the line is shorted to the positive terminal of the power supply.
3. Replace its driver IC .
　　 H. The display is confusing, but the signal output to the next board is normal.
1, the detector 245 corresponding to the latch end of the latch output terminal STB of the driver IC is connected or is shorted to another signal line.
　　 I. Display confusion, output is not normal
1. Detect whether the clock CLK latches the STB signal for short circuit.
2. Detect whether the clock CLK of 245 has input and output.
3. Check if the clock signal is shorted to other lines.
Note: The main detection clock and latch signal.
J. Display lack of color
1. Detect whether there is input and output on the data end of the color of 245 .
2. Detect whether the data signal of this color is short-circuited to other lines.
3. Check whether the cascade data port between the driver ICs of this color has an open circuit or short circuit or a virtual solder. Note: It is easier to find the problem by using the voltage detection method. Check whether the voltage of the data port is different from the normal one and determine the fault area.
　 K. There is a problem with the output.
1. Check whether the line from the output interface to the signal output IC is connected or shorted.
2. Check if the clock latch signal of the output port is normal.
3. Detect whether the cascaded output data port between the last driver IC is connected to the data port of the output interface or is short-circuited.
4. Whether the output signals are shorted to each other or shorted to ground.
5. Check if the output cable is good.
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