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Common faults of LED display motherboard

209 views admin 2023-12-08

Common faults of LED display motherboard

The whole page is not bright

Whether the connection between the power supply and the signal line is normal;

Check whether the test card can recognize the interface. The red light of the test card flashes to indicate that it cannot be recognized. At this time, you should check whether the lamp board and the test card are on the same power ground, or the signal on the lamp board interface is short-circuited to the ground, resulting in the interface being unable to be recognized;

Check whether the chip 74HC245 is soldered or short-circuited, and whether the corresponding enable signal input/output pin on the 74HC245 is soldered or short-circuited to other lines.

Note: The power supply and enable signal should be mainly checked.

(2) During point/line scanning, alternate lines are regularly unlit and the display images overlap.

Check whether there are broken wires, weak soldering, or short circuits between the signal input ports A, B, C, and D to the 74HC245;

Detect whether the A, B, C, D output terminals corresponding to the chip 74HC245 and the 74HC138 are open circuits, soldered, or short circuited;

Detect whether the signals A, B, C, and D are short-circuited or whether a signal is short-circuited to ground.

Note: The signals of lines A, B, C, and D should be mainly detected.

(3) When it is fully lit, some lines or a few lines are not lit.

Detect whether the circuit between chips 74HC138 and 74HC4953 is open, soldered, or short-circuited

(4) During line scanning, two or several lines (usually multiples of 2, with regularity) light up at the same time

Detect whether the signals A, B, C, and D are short-circuited;

Check whether the output terminal of chip 74HC4953 is short-circuited with other output terminals.

(5) There is a single point or multiple points (irregular) that do not light up when fully lit.

Find the control pin corresponding to the module and measure whether it is short-circuited with the current pin;

Replace module or single light.

(6) When it is fully lit, one or several columns are not lit.

Find the pin that controls this column on the module and measure whether it is connected to the output of the driver IC (74HC59S/TB62726)

(7) There is single point or single column highlighting, or entire row highlighting, and it is uncontrolled

Check whether the column is shorted to power ground;

Check whether the positive power supply of this row is short-circuited;

Replace its driver IC.

(8) The display is chaotic, but the signal output to the next board is normal.

Detect whether the STB latch output terminal of the chip 74HC245 is sufficiently connected to the latch terminal of the driver IC, or the signal is short-circuited to other lines.

(9) The display is confusing and the output is abnormal.

Detect whether the clock signal and latch signal are short-circuited;

Detect whether the clock signal of chip 74HC245 has input or output;

Detect whether the clock signal is shorted to other lines.

Note: The clock and latch signals should be mainly detected.

(10)Display lack of color

Detect the corresponding color data terminal of the chip 74HC245 to see whether there is input/output;

Detect the data signal of the corresponding color to see if it is short-circuited to other lines;

Detect the cascaded data ports between the driver ICs of the corresponding colors to see if there are open circuits, short circuits, or false soldering;

Note: The problem can be found relatively easily by using the voltage detection method. By detecting whether the voltage of the data port is different from the normal voltage, the fault area can be determined.

(11) There is a problem with the output

Detect whether the line from the output interface to the driver IC is connected or short-circuited;

Check whether the clock signal and latch signal of the output port are normal enough;

Detect whether the cascaded output data interface between the last driver IC is connected to or short-circuited the data interface of the output interface;

Whether the output signals are short-circuited to each other or to ground;

Check whether the output cable is in good condition.

more articles：https://www.sunriseleddisplay.com/pay-attention-daily-maintenance-outdoor-led-screens-2/

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