white screen
The white screen is caused by the normal backlight and the screen does not receive the signal sent by the main board correctly, which means that the high voltage part is good, and the white screen is because the T-CON board on the upper part of the LCD screen stops working, or works abnormally. It may be caused by the related failure of the circuit that supplies power to the LCD screen T-CON board on the driver board (the voltage is generally 5V, and a few LCD screens use 12V or 3.3V power supply), or the main board control chip and MCU of the display have poor or damaged characteristics. There are chips that have been written into various types of MCU programs for sale on the market. As long as the chip on the original main control board is removed and the new chip that has been programmed is replaced, this kind of failure can be solved.
black screen
In the actual maintenance process, the black screen is mostly the case, and the black screen is divided into three types: power light flashing, long on or off.
(1) The power light of the liquid crystal display flashes. The power light flashes in the maintenance process, mostly due to the short circuit of the rear-stage switch tube of the high-voltage board. When the liquid crystal driver board sends out the control voltage to turn on the high-voltage board, the boost circuit starts to work, but one or a pair of The switch tube is short-circuited to the ground, and the main power supply is pulled down, which causes the power supply of the LCD driver board to be pulled down. Therefore, over and over again, the power light will turn on and off, and the replacement of the corresponding faulty component should be able to solve the problem.
(2) The power light of the liquid crystal display is always on. The power light is always on, which can confirm that the power supply part is normal, mainly because the last stage of the high-voltage inverter circuit or the power supply stage components generate a lot of heat, which is caused by long-term work. The fault is the boost coil, which is generally a problem of poor contact. The circuit should be checked.
(3) The power light of the LCD display is not on. If the power light is not on, the power supply part should be checked. The main thing is to check whether the 12V and 5V voltages are normal. If the power light does not light up, the 12V and 5V voltages should be no output. The key point is to check whether the switch tube is thermally stable. If the performance is not good, or the base is soldered, whether the capacitor has bulging phenomenon, and the pulse width modulation monolithic switching power supply, the pulse width modulation integrated controller generally used is SG6841, UC3842, UC3843, which are also components with high failure rate.
