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The maintenance of iPhone startup constant current and current jump faults

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In this video, we mainly explain the working principle of constant current and current jump

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Let's take a look at how the CPU works

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After the CPU has a power supply, clock signal and reset signal,

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its internal self-test module starts to work,

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and the current will jump slightly once

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If the self-test module fails to start, the current will be set directly after starting up,

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and the current will be around 50mA

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After the self-test module starts successfully,

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it will send clock signal and reset signal for the hard disk

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After the hard disk has power supply, clock signal and reset signal

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the CPU reads the self-test program through the SPI bus

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If the working condition of the hard disk is abnormal, or the data cable is disconnected,

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it will also cause constant current

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At this time, its current will be slightly higher,

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and the current is about 60- 70mA

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After the CPU self-test module reads the self-test program,

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it first test itself, such as the GPU and the upper cover

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If the self-test fails, it will lead to constant current or current cycle jump

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The current at this time is basically around 100mA

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After the self-test of the CPU is completed,

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it starts to self-test the devices connected to the bus

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Generally, it mainly detects the I2C bus,

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and the I2C bus will connect many external devices and chips

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If there is a damage or abnormality, there will also be a constant current jump

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At this time, the current is not 100mA, but around 100-200mA

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If there is no problem with the I2C bus self-test,

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the CPU will read the system boot file in the logic chip

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Then read the system in the hard disk through the PCIe bus

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If there is a problem with the system, or a problem with the logic chip,

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it will also cause constant current or current cycle jump

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At this time, the current is relatively high, around 300mA

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According to the principle, we found that problems with the CPU itself,

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problems with the hard disk,

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and problems with the I2C bus will also lead to constant current and current jump

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In actual maintenance, there is no way to directly judge whether the CPU is good or bad,

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and the hard disk can only be replaced to eliminate

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In actual measurement, we can only measure the bus

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Like these buses, only the I2C bus is convenient for measurement

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Like GPU, hard disk and other bus chips,

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It's not easy to judge

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At this time, we can troubleshoot by brushing the machine and reporting an error

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Because Apple's brushing will proceed from the first step to the last step according to the CPU's workflow

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If there is a problem in any step during the operation,

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it will provide an error code such as 4013, 4014

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4013 is generally a problem with the CPU,

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and 4014 is generally a problem with the upper cover

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Like the CPU and hard disk,

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we can troubleshoot their problems by brushing the machine and reporting an error

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Ok, that's all for this lesson