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Small current when iPhone is turned on

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In this lesson, we mainly talk about the maintenance process of small current

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Maintenance process step 2

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If the CPU power supply is normal,

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we need to measure the CPU clock signal

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The clock signal is provided by the 24M crystal oscillator,

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we need to measure the voltage of the two pins of the crystal oscillator

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The voltage value is around 0.8V,

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and there will be a voltage difference between the two pins

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If there is no voltage when we measure,

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it is possible that the crystal oscillator is damaged

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and we need to replace the crystal oscillator

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If it is still not normal after replacing the crystal oscillator,

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we need to measure whether there is any disconnection between the crystal oscillator pin and the CPU

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Let me demonstrate

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Let's take the iPhone 12 model as an example

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We first find the 24M crystal oscillator in the drawings,

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and the crystal oscillator position number is Y1000

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We go to the bitmap to find the crystal oscillator,

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and then measure the voltage of the two pins of the crystal oscillator

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We measure C1021 and C1020

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The mainboard is powered on, we will measure after the switch is triggered,

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and the measured voltage is 0.57V

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Let's measure another pin,

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and the measured voltage value is 0.59V

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The voltage of the two pins of the crystal oscillator is different,

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which means it is normal

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To make a completely accurate judgment,

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we need to measure the frequency of the crystal oscillator with an oscilloscope

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If it can reach 24M, it means the crystal oscillator is normal

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Next, let's measure the diode value of the crystal oscillator

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The red marker is grounded, and the black marker is measured,

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and the measured value is more than 700

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Let's measure another pin,

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and the measured value is more than 700,

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indicating that the crystal oscillator is not disconnected from the CPU

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Ok, that's all for this video