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In this lesson,

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we will talk about how to repair the power supply of the LCD backlight screen if it fails,

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that is, how to repair if the voltage cannot be measured

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In general, we observe this to show whether there is water corrosion around the chip

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If there is, remove the chip, re-solder,

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generally the problem is solved

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If it is corroded by water and causes poor connection,

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after re-soldering the chip, the fault will be fixed

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If there is no water corrosion,

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we need to measure the ground value of the display power supply

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What is the purpose?

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It is to judge whether there is any abnormality in the power supply line,

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whether there is an open circuit or a short circuit

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If the measured ground value is infinite,

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it means that the circuit is open,

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indicating that there are components that are falsely soldered, or the line is disconnected

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If the measured ground value is 0, it is a short circuit

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This is infinity and short circuit

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If there is no short circuit and no infinity,

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we are going to the next step

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The value of the ground appears infinite or 0,

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how do we analyze it and how to repair it?

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We open Xinzhizao intelligent maintenance system and find Huawei Mate 20,

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we take Mate 20 as an example

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Because the screen power supply of Mate 20 is positive and negative voltage

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This is the component diagram of the Mate 20

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There are obvious marks here, U1701 is the LCD drive chip

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In fact, it is a screen power supply chip,

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or a display chip

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We know its location number,

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we can look it up directly in the circuit diagram,

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search for U1701, we found this chip

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This is its power supply input, the main power supply,

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and its output power supply has two channels

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We search for LCD_VSP, it is connected to the display connector J1701,

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the screen should be buckled on this connector

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Let's take a look at where the seat is shown on the bitmap

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Right-click the mouse, and click find the bitmap components,

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it will automatically jump to the bitmap

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This picture corresponds to the actual display seat,

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the position is exactly the same

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There are a lot of power supply descriptions, signal descriptions on this display connector

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So what are we looking for?

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We're looking for its positive and negative voltage

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LCD_VSN is negative voltage, -5.5 V measurement point,

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pin 13 is positive voltage, LCD_VSP

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We can measure its ground value on these two pins

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That's it for this lesson