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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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Boot steps

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Step 1, buckle the battery or adjustable power supply on the mainboard

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Step 2, the battery or adjustable power supply will reach the charging tube

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or charging chip through the board layer wiring,

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and convert the main power supply

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The main power supply will provide operating voltage for many chips

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If there is a problem with the main power supply,

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it will lead to a large short-circuit of the power connection, or the power connection leakage

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Step 3, in the chips powered by the main power supply,

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the main power supply will work first

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After the main power supply works,

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it will provide the working voltage for the 32.768k crystal oscillator

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Let it generate a 32.768k clock signal and return to the main power supply

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If the crystal oscillator is abnormal,

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it will cause iPhone 11 and above models not to trigger

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iPhone 6-iPhone XS Max will cause constant current or small current fault

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Step 4

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After the main power supply has the main power supply and clock signal,

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it will generate standby power supply

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The name of Apple's full range of standby power supply is PP1V8_ALWAYS

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This power supply provides a pull-up voltage to the switch pin

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If the standby power supply is abnormal, it will cause no trigger fault

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Step 5

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After the switch pin voltage is normal, we trigger the boot

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If the switch pin signal is abnormal, or the switch pin line is disconnected,

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it will cause no trigger fault

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step 6

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After the main power supply receives the power-on signal,

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it will convert the main power supply into more than 30 power supplies

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to provide working voltage for other chips on the mainboard

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There are about 15 high-current BUCK power supplies,

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and about 15 low-current LDO power supplies

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If the BUCK power supply output by the power supply is short-circuited,

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it will cause a large current when starting up

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If there is a short circuit in the LDO power supply,

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the trigger current will be too large

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step 7

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After the power supply of each chip on the mainboard is normal, the CPU will work first

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The CPU will provide the working voltage for the 24M crystal oscillator,

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and let it generate a clock signal and return it to the CPU

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If the crystal oscillator is abnormal,

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it will lead to a small current fault when starting up

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Step 8, after the power supply and clock signal of the CPU are normal,

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a test clock signal will be sent to the main power supply

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This step is less damaged in actual repairs

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Step 9, after the main power supply receives the test clock signal,

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it sends out a reset signal, which includes the reset signal of the CPU

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If the reset signal of the CPU is not normal,

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it will cause the CPU not to work,

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resulting in a small current fault when starting up

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step 10

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After the CPU supplies power, clock signal and reset signal are normal,

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the CPU will send the clock and reset signal to the hard disk to prepare for reading the self-test program

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This step is less damaged in actual repairs

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Step 11, after the hard disk working condition is normal,

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the CPU reads the self-test program stored in the hard disk through the SPI bus

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If the hard disk is damaged or the hard disk is removed,

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it will cause a constant current fault

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Step 12, after the CPU reads the self-test program,

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it first performs a self-test on itself

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Apple's CPU integrates graphics cards and various management modules,

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and the temporary storage is above the CPU

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If the CPU fails the self-test of itself, it will cause a constant current,

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and the current will jump and then stabilize

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Ok, that's it for this video