1. The composition and common failures of LCD screens
The liquid crystal display is generally composed of three parts: a backlight board, a logic board and a display.
a. Backlight board: balance of supply and demand of light display lamp source
Maintenance method:
1. The machine crashes (the light source of the backlight board is not bright), generally because the backlight board is not good.
2. The system crashes (when the time display light flashes once when starting up), it is generally because the backlight board is not good.
Some LCD screens have a backlight panel on the top and bottom of the screen. If all the backlight boards are not good enough, there will be crashes.
b. Logic board: Convert the analog signal presented by the computer motherboard into a logical data signal that manipulates the light transmittance of the liquid crystal display or blocks the light source from passing through
Maintenance method:
1. The machine crashes (the backlight board is on), this type of failure is generally due to poor logic board
2. There are noise on the interface or pigment spots in the image. This type of failure is generally due to poor logic board
C. Display: manipulate the light source to pass or not allow the light source to pass (the display is not good and has not been repaired)
Remark name:
The composition of the LCD screen is very simple, and if the repair is done closely around the backlight board and the logic board, it is enough. Identify the fault category based on the analysis of the fault condition and the substitution of maintenance. The power circuit repairs were subsequently carried out.
Two, drive board repair
1) The simple composition of the driver board is generally composed of switching power supply, high-voltage inverter power supply, control loop and maintenance power supply circuit.
Switching power supply power supply circuit
The total switching power supply of the switching power supply power supply circuit is all due to the balance between the supply and demand of the switching power supply of the TV, which is generally 12V (small display screen) or 24V (display screen). The switching power supply control loop of the driver board is generally as follows
2) The driver board crashes (the backlight board does not light up)
1. The crash (the backlight board is not lit) is mostly due to the failure of the switching power supply principle of the driver board. The switching power supply principle usually has multi-level fuses. The position number of the fuse component generally starts with F. See the diagram below. The most common fuse leads in maintenance. The fuse is usually marked on the power circuit. When it is detected that the fuse leads the way, first check that there is a short circuit fault in the follow-up. If there is no short-circuit fault in the follow-up. The fuse can be dismantled and replaced immediately, and then embrittled and debugged.
2. The control loop power supply of some screens will have a voltage regulator tube or voltage divider circuit. During maintenance, check whether the power supply of the control loop is normal.
C) The driver board crashes (the backlight board flashes and crashes)
1. The backlight board and other sources flicker and crash, usually because the high-voltage inverter power supply and the maintenance power supply circuit are faulty. In this fault, the high-voltage inverter is destroyed more, and the poor position can be judged based on the accurate measurement of the comparative resistance value of several transformers.
2. The other is to maintain the power supply circuit failure. The maintenance power supply circuit is generally located on the left and right sides of the driver board or the key-in end of each transformer. Because there is no engineering drawing, it is often used to accurately measure and repair the reference resistance value. Gradually distinguish the faulty components according to the resistance value of the key link in the maintenance of the power supply circuit of different transformers
Third, the maintenance of the logic board
The logic board is generally composed of power supply, data signal conversion, data signal buffer file power supply circuit.
1. First talk about power supply, because the power supply voltage of the logic board is low, generally below 5V, so the power supply circuit is less faulty. But in the maintenance, still check the power supply resistor or fuse. If there is a power supply resistor or a fuse leading the way, there will be a crash (the backlight is on).
2. Data signal conversion is generally performed by an integrated circuit chip. If there is a crash (the backlight is on), when the power supply is normal, it is most likely that the integrated circuit chip is not good.
3. The data signal buffer file power circuit is generally composed of one or two buffer filers. If the cache filer is not good, there will be patchy effects on the interface, similar to a ringworm-like interface.
4. The logic board has low working voltage and poor component failures. Whether it is a crash or a ringworm-like effect on the interface, the most important thing is that the power circuit and connections are all normal. Therefore, the inspection of the line arrangement is very important. Because of the many pins, the line row is very easy to have virtual connections or false connections. Most of the faults will be checked if the line bar is checked or plugged in again, and everything will be normal. Some wire strip power sockets will have a virtual connection after a few times of plugging, and welding can be done.
Four. Remark name
Because the LCD screen does not have engineering drawings and is more delicate, it is better to choose the resistance measurement repair method in the maintenance as far as possible.
It is best to wear antistatic wrists when repairing, or wash your hands before repairing, and wipe your hands or body with a wet towel. Let go of the electrostatic induction. To prevent unnecessary failures
Because it is difficult to find components with the original model number, components with similar specifications and models should be used as much as possible when substituting components. When substituting a fuse, pay attention to the rated current and current capacity of the fuse. You can't replace it with too much distance, let alone replace it with a short-circuit line.
