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This lesson talks about the maintenance steps of the unreadable card

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Step 5, if there is no abnormality in the above 4 steps,

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you need to install the SIM card on the computer to measure its power supply

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Look at the drawing and find the pins that power the SIM cards

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Its power supply pin is generally VCC

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If the power supply of 1.8 volts cannot be detected, the chip of this power supply source needs to be replaced

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In general mid-to-high-end models, the power supply comes from the NFC chip

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It should be noted here that the mobile phone must be turned on and enter the system

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After installing the SIM card, the card detection signal will become a high level of 1.8 volts

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After becoming high level, the baseband CPU will notify NFC to output power supply

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At this time, if there is no problem with the line, the 1.8 volt power supply can be measured

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If the SIM card is installed after booting, it is normal to measure the power supply of the SIM card,

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but the phone still cannot read the SIM card, you need to go to the sixth step

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Step 6, we need to resolder the baseband CPU or large CPU,

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that is, to resolder the chip leading to the SIM card

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There are currently two types of mobile phones,

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one of which is the baseband integrated in the large CPU, such as the HiSilicon 6290 in the picture

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In addition, Qualcomm's high-end mobile phones also have a baseband integrated in the large CPU.

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There are also some independent basebands, such as HiSilicon 9500, Huawei nova 6

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Their baseband is independent and not included in the big CPU

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And Qualcomm's SDX55M also uses an independent baseband

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Of course, it should also be noted that in many mobile phones,

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the radio frequency transceiver chip will also cause the card not to be read

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First re-solder, if it still doesn't work after re-soldering,

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you can consider replacing a radio frequency transceiver to solve the fault

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That's all for this lesson