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This lesson is about how to repair the no charging fault

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In the third step, plug in the charging cable and measure that there is no 5V power supply around the charging chip,

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indicating that there is a problem with the overvoltage protection circuit

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Next, look at the principle of the overvoltage protection circuit of Android mobile phones of various brands

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The following is the circuit of OPPO's overvoltage protection

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This is the 5V power supply from the tail plug, USB_VCHR

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After the power supply passes through the MOS tube V2801,

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it directly reaches the overvoltage protection chip U2802

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After passing the overvoltage protection chip, output a voltage, USB_VBUS_IN__PMIC,

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which is given to the charging chip

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The voltage here comes from the tail plug connector

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There are two components in this circuit, one is the MOS tube V2801

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If the MOS tube fails, it will cause 5 volts at this end, but there is no 5 volts at this end

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How to solve it at this time?

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Take off this MOS tube and short-circuit its D pole and S pole

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After shorting, this fault can be repaired

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There is another situation

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When the 5V power supply can successfully reach the s pole of the MOS tube,

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it can also reach the b3 pin of the overvoltage protection chip U2802

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But the output can't measure 5 volts

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Then how to solve the fault at this time?

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Remove the U2802 directly and short its input and output to fix the fault

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Of course, you can also find a chip of the same model to replace it

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In this circuit, the actual MOS tube looks like this, with a 1V number

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This overvoltage protection chip is this small rectangular chip

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On the drawing, this is an overvoltage protection chip, generally with 12 pins

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This MOS tube corresponds to the one on the bitmap

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When shorting, you can short these two points, it depends on the specific bitmap

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This is OPPO's overvoltage protection circuit

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That's all for this lesson