A, LCD white screen, white screen phenomenon that the backlight board can work normally, first determine whether the motherboard can work normally, you can press the power switch, see if the indicator has a response, if the indicator can change color, indicating that the motherboard works normally. Check whether there is poor contact between the signal output side of the motherboard and the screen connection line (you can replace the connection line or screen). Check whether the voltage of each working point of the motherboard is normal, especially the power supply voltage of the screen, with an oscilloscope to check the line field signal and clock signal (from input to output), such as the indicator does not respond or does not light, indicating that the motherboard is not working properly.

For 7 inch touch screen, we have different models for customers choice such as 800*480, 1024*600, 800*1280, normal brightness and high brightness.

Check the voltage of each working point of the motherboard, pay attention to the EEPROM voltage (about 4.8V), reset voltage (high and low level, depending on the model), MCU voltage. If there is a short circuit in the power supply, carefully find the location of the short circuit, there may be a short circuit in the copper foil of the PCB. Find out if the microcontroller pins are in good contact with the motherboard: check whether the motherboard chip and microcontroller are working, use an oscilloscope to measure whether the crystal vibration, replace the microcontroller or re-burn the microcontroller if necessary.

II. LCD black screen, the first thing to determine whether the motherboard or backlight board problems, check whether the lights do not respond, if even the lights are not lit, we must check the main board power supply part "with a multimeter to measure the main power point, whether the fuse is blown, if it is blown to disconnect the power supply, with a resistance file to measure the main power point has no short circuit, there is a short circuit to carefully find the line (circuit board copper foil is shorted) and a variety of related components (whether damaged, the whether even tin). If there is no short-circuit phenomenon, then you can refer to the white screen phenomenon maintenance, to ensure that the voltage and signal input and output of the work points are in normal working condition, if the working state of the motherboard are normal, we must check the backlight board.

Check the connection between the motherboard and the backlight board there is no good contact, use a multimeter to measure the voltage of the backlight, to have a 12V supply voltage, to have 3.3V-5V switch voltage and 0-5V backlight adjustment voltage, backlight switch voltage is the most important, if there is no voltage or voltage is too low, to check the microcontroller output level and the working state of the transistor is normal, pay attention to whether there is a short circuit phenomenon. Replace components if necessary

Third, the LCD is missing color, check the main chip to the connection block between the welding is short-circuit (pay attention to the chip feet, chip resistance and connection block, especially the flat socket) check the screen to the motherboard connection lines such as flat cable between whether poor contact, if necessary, replace the motherboard, connection lines, and even the screen to find out where the problem lies.