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iPhone boot process

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This video mainly explains the steps of turning on the iPhone and the common faults caused by different steps

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Step 13, after the CPU self-test is completed, it will initialize the I2C bus,

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and self-test the I2C bus devices

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I2C bus devices include mainboard chips, such as main power supply,

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display power supply, audio amplifier, etc.

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It also includes external equipments,

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such as cameras, displays, touch screens, vibrators, etc.

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If the I2C bus device is short-circuited,

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it will cause the CPU to fail to initialize,

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resulting in a constant current fault

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Sometimes it will cause stuck white Apple, or white Apple restart failure

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Step 14

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After the initialization of I2C bus is completed, the display circuit will be started

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At this time, the phone will display the Apple logo,

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and the current will be around 200mA

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If there is a problem with the display circuit,

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it will cause no display failure

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Step 15

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After the display circuit is started, it reads the system files stored in the hard disk

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If the hard disk is damaged,

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there will be a stuck white Apple or white Apple restart failure

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Step 16

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The CPU reads the configuration file in the logic chip

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Because Apple's logic chip internally stores the system boot configuration file and is bound to the system version

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If the configuration files do not match, it will fail to start,

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and then there will be a white Apple restart or a white Apple failure

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Step 17

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After the configuration of the hard disk system and logic chips is completed,

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it will start the system boot

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If there is a problem with the system,

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there will be a stuck white Apple or white Apple restart failure

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Step 18

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During the system boot process,

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other bus-connected circuits will be initialized again

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Such as PCIE bus, UART bus, SPI bus, etc.

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If there is a problem with the devices connected to these buses,

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it will also cause the stuck white Apple or the white Apple restart failure

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Step 19

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The touch, audio and other circuits are turned on during the system boot process

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Some circuits will automatically shut down after the self-test is completed

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If they fail when other circuits are turned on,

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it will also cause the stuck white Apple or the white Apple restart failure

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Such as audio circuit, Wifi circuit, USB circuit, etc.

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Step 20

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After the application part of the circuit works normally,

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it will turn on the RF circuit when fast forwarding the system

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The RF circuit includes baseband, radio frequency,

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power amplifier chip and other circuits

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If there is a problem with the RF circuit,

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it will also cause the stuck white Apple or the white Apple restart failure

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and sometimes it will also cause a power failure

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Step 21

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If the baseband circuit works normally, it will read the SIM card information

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If no SIM card is installed,

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it will automatically jump to the system interface

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Step 22

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After the baseband reads the SIM card information,

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the receiving channel starts to work

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At this time, the mobile phone will display China Mobile or China Unicom,

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you have to click accept

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If the SIM card is normal,

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but the mobile phone doesn't display China Mobile or China Unicom screen,

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it means that there is a problem with the receiving channel,

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or the SIM card identification circuit is faulty

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Step 23

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After the operator is determined, the transmitting circuit starts to work,

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establishes a connection with the base station, and displays the signal strength

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If there is a problem with the transmission channel,

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the phone will display no service or weak signal

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Step 24

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Boot into the system

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After entering the system, some important information will be prompted,

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such as low battery power, or the screen is not original,

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or the face ID is not available

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Information like these will be prompted immediately after booting into the desktop

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After entering the system, the mobile phone boot process is completed

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Ok, that's all for this video