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This lesson is about maintenance of unreadable SIM cards

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Mainly from the following five aspects

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First, the phenomenon of not reading the SIM card

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Second, the reasons for not recognizing the SIM card

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Third, the working conditions of the SIM card circuit

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Fourth, the relevant circuits of the SIM card work

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Fifth, no card reading failure maintenance

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First look at the phenomenon of not being able to read the card

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Insert the SIM card into the mobile phone, find the SIM card information option in the settings

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If you can see the network operator in the SIM card option, such as China Mobile or China Unicom

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This means that the mobile phone can recognize the SIM card normally.

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If the network operator is not displayed after inserting the SIM card, it means that the card cannot be read

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Look at the upper right corner of the phone,

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there is a cross in the card symbol, which means no card reading

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This is the phenomenon of not reading the card

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Reasons for not reading the card

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The reason for not reading the card can be summarized as that the condition of the SIM card holder is not normal

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Common SIM cards

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As shown in the picture on the right,

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this kind of SIM card holder is welded on the small board of the tail plug,

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and the other one is welded on the big mainboard

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The reasons for not reading the SIM card are as follows

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First, the SIM card seat is corroded by water

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Second, the card seat shrapnel is deformed

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Third, the working conditions are abnormal, that is, there may be abnormalities in power supply, clock, reset, etc.

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Fourth, the baseband CPU fails, resulting in the inability to read the data of the SIM card,

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which is the failure of the baseband circuit

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There are four major reasons for not reading the card

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That's all for this lesson