Led large screen just power on a few seconds of bright lines or the screen screen screen becomes flowery reasons?

Current answer is adopted as the best

LED large screen just power on a few seconds of bright lines or the screen screen screen becomes flowery phenomenon, mainly due to the following reasons:

I. Normal self-test phenomenon
system startup self-test
When the LED screen is powered on for the first time, the control system will carry out hardware self-test, at this time the screen may appear briefly (about 2 seconds) bright lines or "splash screen" phenomenon. This is a normal test process, used to confirm the screen module, signal transmission and power supply and other basic functions are normal.
Note: This phenomenon is similar to the hardware detection prompt when the computer is turned on, which is part of the design logic and does not require special treatment.

Power initialization process
The controller needs to gradually enter the stable working mode from the completely power-off state, and the voltage fluctuation of the power supply module may cause the display unit to be abnormal for a short period of time. Make sure that the controller is properly connected to the +5V power supply (not directly connected to the 220V power supply) to avoid interference.

II. Troubleshooting for abnormal conditions
If the bright line or splash screen persists (for more than 2 seconds), the following reasons may be the cause:

Control card setup or wiring problems

Scanning parameter error: The scanning mode set by the control card does not match the actual hardware (e.g., wrong configuration of the unit board row/column driver).
Abnormal wiring connection: Check whether the wiring from the control card to the first unit board is loose, reversed or damaged.
Power problems

Unstable voltage: Measure whether the power supply output is within the range of 4.9~5.5V, if it is out of the range, it may damage the unit board or control card.
Misconnection of strong power: If the 220V power supply is connected to the controller by mistake, it may lead to transient current shock and cause display abnormality.
signaling fault

Loose communication cable: Check if the serial cable is straight through and firmly connected, crossed wires or loose will cause signal interruption.
Driver IC cascade problem: If the output data port of the last driver IC is short-circuited or not connected, it may affect the signal reception of the subsequent modules.
III. Recommended operations
Normal phenomena do not need to be dealt with: if only a short self-test, can be ignored.
Steps to take in case of persistent exceptions:
Check power supply voltage and connections;
Re-insert the wires and make sure they are oriented correctly;
Verify that the control card parameters match the hardware;
Contact factory technical support or send in a unit board for repair.
If the problem is still not solved, it is recommended to contact a professional to further detect hardware damage (e.g. control card, driver IC, etc.)