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iPhone touch circuit repairing

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In this video, we're going to learn about the working principle of the iPhone 12 Promax touch chip

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

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the main power supply will output 1.8V and 1.2V power supplies to provide the working voltage for the touch chip

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Step 2, after booting up and the CPU working condition is normal,

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it will detect the touch chip through the I2C bus

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The I2C bus is the same as the I2C bus of the touch screen

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Step 3, when the touch circuit is started,

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the CPU will send a 24MHz clock signal for the touch chip

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Step 4, after the CPU sends the clock signal, it sends a reset signal for the touch chip

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Step 5, after the touch chip has power supply, clock signal and reset signal,

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the CPU will read the touch chip through the SPI bus

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Step 6, after the touch chip has SPI data,

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it will detect the touch screen through the SPI bus

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If the touch screen can be read and recognized,

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the touch chip will send the TOUCH_LDO_EN to the main power supply

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Step 7, after the main power supply receives the LDO_EN turn-on signal,

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it will output 3.1V power supply

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One way provides the working voltage for the touch screen,

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and the other way provides the working voltage for the touch chip

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

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then it will send an interrupt signal to notify the CPU

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Step 9, after the CPU receives the interrupt signal,

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it will receive the data of the touch chip through the SPI bus

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After the CPU receives the touch data, it will perform the corresponding action

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These working conditions are the necessary working conditions for the touch chip to convert signals normally

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If one of the conditions is abnormal, it will cause a no touch failure

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In addition to these signals in the functional block diagram, there are some 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_HIFA is the first display touch synchronization signal sent from the display to the touch chip

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The UART bus is the bus required to transmit data when other circuits use the touch screen,

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such as 3D touch function

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Because the 12 Promax has a touch chip, the data is sent directly to the touch chip

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In other models, the data is sent to the touch screen by the CPU through the UART bus

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SWD bus is a serial debug bus

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When some signals are tested, they need to be transmitted through the SWD bus

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These signals belong to the working conditions of the touch chip

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If we overhaul the touch circuit and replace the touch chip,

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the touch screen still cannot work normally,

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we need to overhaul the working conditions of the touch chip

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When measuring, it is necessary to measure all the signals

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Ok, that's all for this video