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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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Let's take a look at this positive voltage line

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From here to here, through this LB1707,

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this magnetic bead is the inductor

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The other end of it reaches the filter capacitor, and through this resistor,

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it reaches the E3 pin of the power supply chip U1701,

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and the power supply is output from here

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We have to keep the pathway of the circuit in mind

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The power supply passes through the resistor and this filter capacitor, reaches the inductor,

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and then reaches the seat after passing through the inductor, which is the path of the power supply

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If we measure the ground value here to infinity,

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how should we think about it?

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This pin 13 is positive voltage, LCD_VSP

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When we measure it here, we use a black pen to measure it

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Infinity appears, how should we analyze it?

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Because this is a power supply,

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it must have a ground value when the power supply leads to the chip

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If there is an OL on the ground value, there is a problem,

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which may cause no display

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At this time, we have to consider the inductor in the line

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If there is no problem with the inductor,

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then there is a problem with the chip U1701

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We can measure the ground value to measure whether there is a problem with this inductor

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We can take it off and short its two pins with a wire

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However, there is a condition,

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that is, there is a value here, but there is no value here

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Basically, short the inductor and the fault will be repaired

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This is a situation

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When are we going to think about the display chip?

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This end of the inductor is directly connected to the chip

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If we measure that this end has no value,

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we should not short-circuit the inductor

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The fault has nothing to do with this inductor.

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We have to re-solder the chip U1701

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If it still doesn't work after re-soldering, we have to replace the chip

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Well, this is the analysis of the infinite value of the ground

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There is a problem to pay attention to

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When we measure the negative voltage,

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we need to use the red test pen to measure, and the black pen to ground,

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so that the normal ground value can be measured

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The analysis method is the same

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That is, we have to first test whether this end has infinity

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The right end of LB1708 leads to the chip

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If this end has a value, we can directly short the inductor to solve the problem

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If there is no value at this end, we need to re-solder the chip

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If it still doesn't work after re-soldering, we have to replace the chip

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Okay, that's all for this lesson