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We continue this lesson on no trigger maintenance

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As we learned earlier,

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if we can't measure the 1.8 volts of the power button,

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we have to measure the main power supply that powers the power supply

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If the main power supply has no voltage,

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the power supply is not capable of outputting the 1.8 volts on the power button

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Well, let's take a look,

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how do we find the voltage of this main power supply line and where to measure it

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We open the PCB bitmap of Xiaomi 10

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and the schematic diagram of the mainboard

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We know that Xiaomi's main power supply is VPH_PWR

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Well, we can easily find it

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Right-click in the schematic and click Find Bitmap

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At this time, we can measure the main power supply voltage

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at these yellow highlighted positions

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We click here in the lower left corner,

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it will show what is currently highlighted

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For example, this is the vph_pwr,

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That is to say, in these yellow highlighted positions,

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we can test the main power supply

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If the main power supply has no voltage,

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we need to replace the charging chip

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If the main power supply has no voltage,

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the power button will not be measured 1.8 volts

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There are several reasons why the main power supply cannot measure the voltage of 4 volts

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One is whether the charging chip is abnormal,

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and the other is whether the battery power supply is normal

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Let's take Xiaomi 10 model as an example

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Open the circuit diagram

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We talked about its conversion main power supply principle earlier,

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the chip U5200 is the charging chip

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This charging chip is responsible for turning on the positive voltage

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of the battery through the internal MOS tube,

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and outputting the main power supply from here

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Where is the battery voltage measured?

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It can be measured on the pins of these capacitors on the battery line

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If we want to measure whether the battery voltage is normal,

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after buttoning the battery holder, we can measure it here

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For example, on this capacitor,

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of course, it can also be measured on the charging chip

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If we can't measure the voltage here,

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but we can measure the battery voltage here

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Then we have to re-solder the charging chip U5200

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If the main power supply still cannot be measured after re-soldering,

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we have to replace the charging chip

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When we measure the battery voltage around the charging chip,

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if the battery voltage is 4.3-4.4 volts, it is OK

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if the voltage cannot be measured,

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then we have to replace the charging chip

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Okay, that's it for this lesson