Description of Malfunction |
Cause of Malfunction |
Analytical Processing |
1. One unit panel cannot work. |
1. The +5V or GND is not available. |
Supply the +5V or GND |
2. Short circuit of +5V and GND |
Break the short circuit |
3. The OE signal of the fifth pin of the 74HC138 chip is not supplied. |
Supply the OE signal |
4. The OE signal connected with the 74HC245 chip is abnormal (open or short circuit). |
Connect the open circuit and break the short circuit |
2. The upper part or the lower half of the unit panel doesn't work or the unit panel displays abnormally. |
1. The OE signal of the fifth pin of the 74HC138 chip is not supplied. |
Connect the OE signal |
2. The signals of the eleventh and twelfth pins of the 74HC595 chip are abnormal. (SCLK,RCK) |
Connect the SCLK and RCK signals |
3. The connected OE signal is abnormal. |
Connect the open circuit and break the short circuit |
4. The SCLK and RCK signals of the double pin with the 74HC245 chip are abnormal (broken circuit or short circuit). |
Connect the broken circuit and break the short circuit |
3. One row LEDs on the unit panel or on the corresponding module fail to work or display abnormally. |
1. The base pin corresponding to the line signal on the module comes out with rosin joint or solder skip. |
Weld the base pin to eliminate the rosin joint or solder skip |
2. The line signal is disconnected with the base pin on the TIP127 or 4953 chip, or happens to be short circuit with other signals. |
Connect the broken circuit and break the short circuit |
3. The pull-up or pull-down resistors on the line signal are not welded or welded not very well. |
Make sure all the pull-up and pull-down resistors are welded well enough. |
4. The output line signal of 74HC138 is disconnected with the corresponding TIP127 or 4953 chip. Or the short circuit happens between the output line signal of 74HC138 and other signals. |
Connect the broken circuit and break the short circuit |
4. Two rows of LEDs on one unit panel light at the same time with one normal row and the other row lighting always when displaying the text. |
1. Check the short circuit to the two line signals corresponding to the module. |
Break the short circuit |
2. Check the short circuit to the output pin of the 74HC138, pull-up and pull-down resistors, module base pin and TIP127. |
Break the short circuit |
5. At the upper half or the lower half, the LEDs generating red or green color fail to work or display abnormally. |
1. Check the pins of the input row of the short circuit with the GND and +5V. |
Connect the open circuit |
2. Check the short circuit or open circuit of the signals from pins of input row to 74HC245 chip. |
Break the short circuit |
3. IC245 chip is broken. |
Replace the IC245 chip |