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iPhone audio circuit repairing

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This video mainly explains the working principle of audio power amplifier

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The audio amplifiers of iPhone XR to 11 ProMax models work the same

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Audio power amplifier refers to earpiece power amplifier and speaker power amplifier,

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which is a chip used to enhance sound

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In the iPhone, the earpiece amplifier and the speaker amplifier have the same model

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and the same working principle,

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but there are some differences in the signal

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There is a PDM bus when the signal of the earpiece power amplifier is transmitted,

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but there is no PDM bus for the speaker power amplifier

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The first step of the working principle,

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when the battery is buckled or the adjustable power supply is connected,

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the main power supply will be generated,

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and the main power supply will first provide the working voltage for the audio amplifier

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Step 2, after triggering the boot, the main power supply will output many power supplies,

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among which 1.2V and 1.8V power supplies will provide working voltage for the audio amplifier again

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Step 3, after the CPU working condition is normal,

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it will detect the audio power amplifier through the I2C bus

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Step 4, when starting to the audio circuit,

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the CPU will first send a clock signal to the audio power amplifier

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Step 5, the CPU sends a reset signal for the audio power amplifier

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The reset signal is sent by the power supply in some circuits, and some are sent by the CPU,

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according to the drawing identification shall prevail

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Step 6, after the audio power amplifier has the power supply, clock signal and reset signal,

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the audio power amplifier can work normally

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At this time, the audio power amplifier will send an interrupt signal to notify the CPU

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Step 7, when using the audio function,

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the audio chip will send audio data to the audio amplifier through the I2S bus

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Step 8, after the audio amplifier receives the audio data, it will generate a boost

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Step 9, after the boosting of the audio power amplifier is completed,

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the boosted power supply will be loaded to the output signal through the internal conversion module,

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and sent to the earpiece speaker or the bottom speaker,

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and the speaker will produce sound after it has the positive and negative signals

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When we answer the phone, the audio chip will send audio data to the handset amplifier through the PDM bus

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After receiving the PDM audio data, the earpiece power amplifier will not boost the voltage,

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and directly output to the earpiece speaker through the output pin

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Because there is no boost, the sound from the earpiece speaker is relatively small

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When there is no earpiece or no sound from the speaker,

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we need to check the working conditions of the audio amplifier

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If there is an abnormality in the working condition of the audio power amplifier,

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it will cause no sound failure

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That's all for this video