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Analysis of failure caused by damage of screen logic board

Update Time : 2018-05-03 View : 3941
The failure phenomena caused by the damage of screen logic board are: black screen, white screen, gray screen, negative image, noise wave point, vertical band, too bright or too dark image. Different LCD screens need to choose different LVDS programs. When the program does not match, there will be more color misalignment or abnormal images, that is, the usually said screen parameter is wrong. The normal image can be restored by the bus adjustment, which is not within the scope of this discussion. The following is the maintenance process and principle of the normal line of line lines.
Some TV sets in the logic board circuit are a separate circuit board. Some are connected to the screen. A separate logic board can be used to repair the board. In the maintenance process that is connected to the screen, it must be careful to avoid damage or high temperature damage to the field module and the LCD screen.
White screen fault occupies a large proportion in actual maintenance. First, we need to check 3 voltages when we encounter white screen failure.
1. The screen power supply voltage is 5V or 12V,
2, VGH: Vgatehigh refers to the gate level high potential, that is, to open the voltage of gate level. 18V---24v
3, VGL: Vgatelow, is the low potential of the gate level, that is, to turn off the voltage of the gate level. This voltage is effective at the two order drive. In the three order drive, this voltage is only used to produce Vgoffl;
VGH is the voltage 18V or 24V generated by the power supply voltage of 5V or 12V after the output of a DC----DC conversion circuit is determined by the screen. VGL negative 7V, it is also output from the DC---DC transform circuit. The general screen circuit these three voltages are normal, the final consideration of the main chip; the general screen DC conversion circuit, the first to check the filter capacitance, the second is the DC---DC circuit, IC bad, check the above steps if not repaired, it is suggested to replace the logical board directly, if it is a single screen, then only a screen replacement The failure rate of gamma correction circuit is not very high, so it is not discussed.
There is a vertical line in the LCD LCD screen. Because the film module connected to the screen is completed by a professional screen machine, the general maintenance department does not have the equipment, so it can be treated with hot air gun and aluminum sheet. Because the winding line is made of soft plastic, it can not be heated directly by hot air gun. It uses aluminum sheet to press the line and then heat the aluminum radiator. Do not loose with hands, temperature control at 200 degrees Celsius, too high will burn out the line, the wind gun temperature to own good or the screen will be useless, if it can not be repaired that can only be scrapped, and some liquid crystal LCD screen vertical line is because the screen circuit damage, this is not maintenance.

The general fault judgment is as follows:
1, flower screen generally check the LVDS connection, mostly at the interface, loose or wet, and chips are also bad.
2, adjust the menu messy code, is the motherboard failure, replace the main chip or memory, or directly replace the motherboard.
3, black screen failure, mostly backlight circuit failure, a small part of the motherboard failure.
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