1. Module not lit: The module is not connected to power; the input cable is reversed; the input and output are reversed; the power supply polarity is reversed.
2. Module not lit but transmission is normal: The protection circuit is damaged. The solution is to short-circuit pins 4 and 5 of the 74HC138.
3. One line out of three is not lit: The 4953 is damaged (one of them is faulty).
4. One line lit every other line: The A signal is faulty. Please check if the 74HC245 and 74HC138 have poor soldering; use a multimeter to check if the voltage at pin 1 of the 74HC138 is approximately 2.5V. If so, replace the 74HC138; carefully check the path of the gold pins carrying the ICA signal.
5. Two lines light up every other line: This is a B signal issue. Please check for cold solder joints on 74HC245 and 74HC138. Use a multimeter to check if the voltage at pin 2 of 74HC138 is approximately 2.5V. If so, replace 74HC138. Carefully check the path of the gold pins carrying the ICA signal.
6. Upper half of the board is normal, lower half is fully lit or not lit: If this occurs with the T08A interface, check if the DR data signal of the lower 8 lines is working. If normal, replace 74HC245 first. If not, replace the first 74HC595.
7. On this board, the STB and CLK signals are shared between the upper and lower half, but the data is separate (if it's a T12 interface, the data is also one). If checking the T08A board, the upper and lower half must be checked separately.
8. If one LED on the board is not lit: Check for cold solder joints and replace the LED.
9. Four vertical LEDs are not lit: First, check if the 74HC595 has a cold solder joint; second, replace the 74HC595; third, replace the LED tubes.
10. Three out of four vertical LEDs are not lit, and one is working: Replace the working LED tube.
11. If the module displays abnormally from the middle or other positions: Check the data signal path; replace the 74HC595 controlling the last working LED; if this does not resolve the issue, replace the 74HC595 controlling the first non-working LED. Each 74HC595 controls an 8-dot wide * 4-dot high LED. The 74HC595s are connected in series using DR data signals, meaning the DR signal enters from pin 14 of the 74HC595, exits from pin 9, connects to pin 14 of the next 74HC595, and so on until the last 74HC595. For example, on this board, the DR data goes from the gold pin to the 74HC345, is amplified, then goes to UR1, UR2, UR3, and so on until UR8, and finally to the output gold pin. 12. Sometimes, during the debugging of the entire screen, the display of the modules from the front to the back may be abnormal. The common problem is a loose or damaged ribbon cable. You can try using a slightly longer ribbon cable to connect the correctly functioning module below to the malfunctioning module above to see how the display changes. Alternatively, you can connect the output of a normally functioning module preceding the malfunctioning module above to the next row of modules to see how the display changes and identify the faulty module.
