1、 LCD display white screen
A. The appearance of a white screen indicates that the backlight board is working properly. First, determine whether the motherboard is working properly. You can press the power switch to check if the indicator lights are responding. If the indicator lights can change color, it indicates that the motherboard is working properly
1. Check if there is any poor contact in the connection wire between the motherboard signal output and the screen (the connection wire or screen can be replaced)
2. Check if the voltage at each working point of the motherboard is normal, especially the power supply voltage of the screen
3. Use an oscilloscope to check the on-site signal and clock signal (from input to output)
B. If the indicator light is unresponsive or not on, it indicates that the motherboard is not working properly
1. Check the voltage of each working point on the motherboard, paying attention to the voltage of EEPROM (about 4.8V), reset voltage (high or low, depending on the model), MCU voltage. If there is a power short circuit, carefully search for the location of the short circuit, as there is a possibility of a short circuit in the copper foil of the PCB board
2. Check if the contact between each pin of the MCU and the motherboard is good
3. Check if the motherboard chip and MCU are working, and use an oscilloscope to measure whether the crystal oscillator is vibrating
4. Replace the MCU or re burn it if necessary;
2、 LCD display screen black
A. Firstly, it is necessary to determine whether it is a problem with the motherboard or backlight board. You can check if the indicator lights are working properly. If even the indicator lights are not lit, you need to check the power supply of the motherboard
1. Use a multimeter to measure the working points of each main power supply and check if the fuse is blown. If it is, disconnect the power supply. Use a resistance gauge to measure whether there is a short circuit at the working points of each main power supply. If a short circuit occurs, carefully locate the wires (whether there is a short circuit in the circuit board copper foil) and various related components (whether they are damaged or soldered)
If there is no short circuit phenomenon, repair can refer to the white screen phenomenon to ensure that the input and output of voltage and signal at each working point are in normal working state
B. If the motherboard is working properly, check the backlight board
1. Check if the connection between the motherboard and the backlight board is in good contact
2. Use a multimeter to measure the voltage of the backlight. There should be a 12V power supply voltage, a 3.3V-5V switching voltage, and a 0-5V backlight adjustment voltage. The switching voltage of the backlight is the most important. If there is no voltage or low voltage, check the output level of the MCU and the working status of the transistor, pay attention to any short circuits, and replace all components if necessary
3、 LCD display lacks color
1. Check for short circuits and solder joints between the main chip and the connection socket (pay attention to chip pins, chip shaped resistors, and connection sockets, especially flat sockets)
2. Check for poor contact between the connection wires from the screen to the motherboard, such as flat cables
3. If necessary, replace the motherboard, connecting wires, and even the screen to identify the problem
4、 LCD display button malfunction
1. Measure the ground voltage of each button. If the voltage is too low or 0, check if there is a short circuit, open circuit, incorrect values and solder joints in the pull-up resistance of the circuit from the button board to the MCU, and if there is poor contact between the socket and connecting wires
2. Pay attention to whether the buttons themselves are damaged

5、 The dual color indicator light on the LCD monitor is not on or only one color is on
1. Check the circuit of the indicator light, whether the level of the transistor controlled by the indicator light is normal, usually a high level of 3.3V and a low level of 0V. When switching the switch, the two levels will become opposite. If it is abnormal, check for short circuits or virtual soldering between the circuit and the MCU
2. Check whether the power supply voltage (5V) of the transistor is normal, whether the output of the transistor is normal, and measure the voltage at both ends of the indicator light
3. Check for poor contact between the motherboard socket and the button board, and for any short circuit to ground on the circuit board
4. It is necessary to replace the indicator light
6、 LCD monitor color deviation
1. Check the circuit of the motherboard signal R \ G \ B from the input to the main chip (whether there is a short circuit due to virtual soldering, and whether there are incorrect values in the capacitance and resistance)
2. Enter factory mode and perform white balance adjustment to see if the normal color can be adjusted
3. Replace the MCU or re burn it if necessary
7、 LCD display screen mosaic
1. Measure whether the clock output of the motherboard is normal
2. Check the circuit of the motherboard signal R \ G \ B from the input to the main chip (whether there is a short circuit due to virtual soldering, and whether there are incorrect values in the capacitance and resistance)
3. Check if there is a short circuit due to virtual soldering in the connection socket of the motherboard signal output to the screen (IC pin resistance and socket double row pins, pay special attention to flat sockets)
4. Replace the screen if necessary
8、 LCD display has no signal
A. No VGA Input appears after power on
1. Check the VGA cable connection
2. Check the circuit of the motherboard from the line input (pay attention to whether there is a short circuit between the line input and ground of the VGA mother socket) to the inverter output and then to the main chip (whether there is a short circuit due to virtual soldering, and whether there is an incorrect value in the capacitance and resistance)
3. Check the voltage at each working point of the motherboard (possibly due to damage to the main chip)
B. After power on, there is a display of VGA NOT SUPERT or FREQENCY OUT OF RANGE exceeding the limit
1. Check if the computer input signal is out of range
2. Check the voltage at each working point of the motherboard (possibly due to damage to the main chip)
9、 LCD screen flicker (word jitter)
Can the "phase" be adjusted properly using automatic or manual adjustment
2. Check the voltage at each working point of the motherboard (possibly due to damage to the main chip)
3. Check for any incorrect values in the capacitance and resistance of the phase-locked circuit
4. Check the circuit of the motherboard from the field input to the inverter output and then to the main chip (whether there is any virtual soldering, short circuit, capacitance, resistance, or incorrect value)
10、 LCD display ghosting
1. Check the input signal to see if it is caused by connection allocation or if the VGA cable is not up to specification
2. Check if the VGA socket on the motherboard is poorly soldered or connected
3. Check if there are any solder joints, short circuits, or incorrect capacitance or resistance values in the circuit from the signal input to the chip on the motherboard
4. Check the voltage at each working point of the motherboard (possibly due to damage to the main chip)