Common Faults of LED Display Control Boards
Created on 04.22
(1) Entire Board Not Lighting Up
- Verify whether the power supply and signal cable connections are functioning properly.
- Check whether the test card can correctly detect the interface. If the red indicator on the test card is flashing, it indicates that the interface cannot be identified. In this case, inspect whether the display module and test card share a common ground, or if there is a short circuit between signal and ground at the module interface.
- Inspect the 74HC245 chip for cold solder joints or short circuits, and verify whether the corresponding enable signal input/output pins are properly connected and not shorted to other lines.
Note: Priority should be given to checking the power supply and enable signals.
(2) Regular Missing Lines During Point/Line Scanning; Overlapping Display
- Check for open circuits, cold solder joints, or short circuits between the A, B, C, and D signal inputs and the 74HC245.
- Verify connections between the A, B, C, and D outputs of the 74HC245and the 74HC138.
- Check for short circuits among A, B, C, and D signals, or between any signal and ground.
Note: Focus primarily on the row selection signals A, B, C, and D.
(3) One or More Rows Not Lighting During Full Illumination
- Inspect the connections between 74HC138 and 74HC4953 for open circuits, cold solder joints, or short circuits.
(4) Multiple Rows (Typically in Powers of Two) Lighting Simultaneously During Row Scanning
- Check for short circuits among A, B, C, and D signals.
- Verify whether outputs of the 74HC4953 are shorted to other outputs.
(5) Random Single or Multiple Pixels Not Lighting During Full Illumination
- Locate the control pin corresponding to the faulty module and measure whether it is shorted to the row line.
- Replace the module or the individual LED if necessary.
(6) One or More Columns Not Lighting During Full Illumination
- Identify the control pin for the affected column on the module and verify whether it is properly connected to the output of the driver IC (e.g., 74HC595/TB62726.)
(7) Single Pixel, Column, or Entire Row Stuck at High Brightness and Uncontrollable
- Check whether the affected column is shorted to ground.
- Verify whether the affected row is shorted to the positive supply voltage.
- Replace the corresponding driver IC if required.
(8) Display Disorder with Normal Signal Output to the Next Board
- Check whether the STB (latch) output of the 74HC245 is properly connected to the latch input of the driver IC, or if the signal is shorted to other lines.
(9) Display Disorder with Abnormal Output
- Check whether the clock signal and latch signal are shorted.
- Verify whether the 74HC245 is receiving and outputting the clock signal correctly.
- Check whether the clock signal is shorted to other lines.
Note: Focus primarily on the clock and latch signals.
(10) Missing Color in Display
- Check whether the corresponding color data pins of the 74HC245 have proper input/output signals.
- Verify whether the color data signals are shorted to other lines.
- Inspect cascade data connections between driver ICs for open circuits, short circuits, or cold solder joints.
Note: Voltage measurement is an effective method for fault localization. Compare the voltage levels at data pins with normal values to identify faulty areas.
(11) Output Abnormalities
- Check whether the connections between the output interface and the driver IC are intact or shorted.
- Verify whether the clock and latch signals at the output interface are functioning properly.
- Inspect whether the cascade output data interface of the last driver IC is correctly connected to the output interface or shorted.
- Check for short circuits among output signals or between signals and ground.
- Ensure that the output ribbon cable is in good condition.
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