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This lesson talks about the maintenance for no baseband fault of mobile phone

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with baseband CPU integrated in large CPU

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For mobile phones that can boot into the system normally, a large CPU will generally not cause no baseband,

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so there is no need to consider a large CPU,

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that is to say, a large CPU will not cause no baseband failure

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We mainly consider the circuits of the RF chip and the WiFi chip,

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both of which will cause no baseband

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Of course, not all radio frequency or WiFi of mobile phones will cause no baseband

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This kind of RF chip and WiFi chip using Qlink bus,

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their circuit failure will lead to no baseband,

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generally the working conditions of the circuit are not satisfied or the working conditions are lacking

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The RF chip or WiFi chip using the IQ bus will not cause no baseband

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For example, Huawei mobile phones use the Qlink bus

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Its Qlink bus is generally referred to as USR DL or USR UL, which is actually the Qlink bus

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Then the Qlink bus of the Xiaomi mobile phone is more straightforward

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Generally, the code name Qlink is directly on the RF IC chip

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First check whether the WiFi can be turned on normally

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If the WiFi cannot be turned on normally, first repair the WiFi circuit,

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and the baseband will return to normal

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For example, in the picture, you get a mobile phone without a baseband,

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click on WiFi, and it cannot be opened normally

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It means that the baseband cannot be turned on due to the failure of WiFi,

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and the WiFi circuit can be repaired first

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When the WiFi can be turned on normally, but the mobile phone still has no baseband,

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it is necessary to check the working conditions of the RF transceiver

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Generally, the main test is the power supply and clock signal

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The power supply is generally measured to see if there is a short circuit to the ground value

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If there is a short circuit, it is necessary to repair the short circuit fault, and the general fault can be solved

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If there is no short circuit, turn on the power supply to measure

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whether the voltage of the power supply is normal

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If the voltage of the power supply is missing, it is necessary to find the source of the power supply

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Generally, the power supply is provided by other chips,

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and the resistance will be connected in series during the process of supplying the radio frequency

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Using the voltage method to check the voltage can also roughly judge whether the clock is normal

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In the process of the clock leading to the RF chip, a capacitor is generally connected in series

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We measure the voltage across the capacitor

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If the voltage difference is particularly large, there is a problem with the clock signal

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If the ground value is measured in the power-off state,

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it should be noted that the capacitor connected in series is easy to misjudge

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It is normal for ground value infinity

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This is the maintenance for no baseband fault of mobile phone with baseband CPU integrated in large CPU

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That's all for this lesson