In the actual maintenance process, black screens are more common, and black screens can be divided into three types: flashing power lights, long on, or off.
(1) During the maintenance process, the flashing power light of the LCD display is often caused by a short circuit in the rear switch tube of the high-voltage board. When the LCD driver board sends out the control voltage to open the high-voltage board, the boost circuit starts to work. However, one or a pair of switch tubes are short circuited to ground, pulling down the main power supply, causing the power supply to the LCD driver board to also be pulled down. When the power supply to the LCD board is abnormal, the signal to open the high-voltage board is immediately revoked, The voltage output of the power board has returned to normal, so repeatedly, the power light turns on and off. Replacing the corresponding faulty component should solve the problem.
(2) The LCD display power light is on for a long time, which can confirm that the power supply is normal. This is mainly due to the high heat generated by the final stage or power supply components of the high-voltage inverter circuit, which causes virtual soldering due to long-term operation; The most likely cause of malfunction in this circuit is the boost coil, which is usually a problem of poor contact. Therefore, it is important to focus on inspecting this circuit.
(3) If the power light of the LCD monitor is not on, the focus should be on checking the power supply. The main focus should be on checking whether the 12V and 5V voltage is normal. If the power light is not on, the 12V and 5V voltage should not be output. The focus should be on checking whether the switch tube has poor thermal stability, or if the base is soldered, or if there is any bulging phenomenon in the capacitor. In addition, for pulse width modulation single chip switching power supplies, the pulse width modulation integrated controllers used are generally SG6841, UC3842 UC3843 is also a component with a high failure rate.
