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iPhone touch circuit repairing

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This video mainly explains the working principle of the iPhone 12 Promax touch circuit

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The display and touch connectors of the iPhone 12 Promax are the same

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And there is a touch chip in the mainboard of this model

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The main function of the touch chip is to convert the data between the touch chip and the CPU

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The first step of the working principle, after we trigger the switch,

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the main power supply will output more than 30 channels of power supply

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Among them, the 1.8V power supply will first provide the working voltage for the touch screen

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Step 2, CPU working condition is normal after power on, it will detect the touch screen through the I2C bus

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Step 3, when the touch circuit is started, the main power supply sends a 32KHz clock signal to the touch screen

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Step 4, when the touch circuit is started,

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the touch chip sends a reset signal to the touch screen

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Step 5, after the touch screen has 1.8V power supply, clock signal and reset signal,

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the touch chip will detect the touch screen through the SPI bus

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Step 6, after the detection,

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the touch chip will send an LDO_EN signal for the power supply

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Step 7, when the main power supply receives the LDO_EN signal,

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it sends out the 3.1V power supply for the touch screen

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Step 8, after the touch screen has 3.1V power supply, all working conditions are normal,

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and an interrupt signal will be sent to notify the touch chip

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Step 9, after the touch chip receives the interrupt signal,

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it will send touch data to the touch screen through the SPI bus

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Then the touch screen can work normally

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These signals are the main signals when the touch screen is working

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In the block diagram, the touch screen has other detection signals

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MANY_SCAN is the forced synchronization signal of the touch screen

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This signal is sent by the touch screen to the power supply, camera power supply and other chips

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TOUCH_AID is the ID identification signal sent by USB to the touch screen

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TOUCH_HIFA is the first display touch synchronization signal sent from the display to the touch chip

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BSYNC is the second display touch synchronization signal sent from the display to the touch chip

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In the functional block diagram,

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these signals are important working conditions required for the touch screen to work

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If one signal is abnormal, it will cause no touch failure

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When we troubleshoot no touch faults, we first measure the main signals

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If there is no problem with the main signals, we measure the other detection signals

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Ok, that's all for this video