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iPhone touch circuit repairing
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This video mainly explains the working principle of iPhone 12 and 12Pro touch circuits
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The first step of the working principle, 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 provide the working voltage for the touch 5.1V conversion chip
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Step 2, when the power is turned on,
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the main power supply will output more than 30 channels of power supply
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Among them, 1.8V_IO power supply and 1.8V_TOUCH power supply
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will provide working voltage for the touch screen
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Step 3, after the working condition of the CPU is normal,
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it will read the screen data storage core on the touch cable through the I2C bus
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Step 4, when starting to the touch circuit,
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the main power supply sends a 32K clock signal for the touch screen
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Step 5, when starting to the touch circuit,
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the CPU sends a reset signal for the touch screen
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Step 6, when the touch screen has 1.8V power supply, clock signal and reset signal,
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the CPU will read and detect the touch screen through the SPI bus
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Step 7, after the CPU detects the touch screen,
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the touch screen will send a 5.1V turn-on signal to the conversion chip
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Step 8, after U8900 receives the turn-on signal,
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it will generate 5.5V power supply to U8910
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After U8910 has 5.5V power supply and turn-on signal,
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it will convert it to 5.1V power supply of the touch screen
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Step 9, after the touch screen has 1.8V, 5.1V power supplies, clock signal and reset signal,
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the touch screen can work normally
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At this time, the touch screen will send an interrupt signal to notify the CPU
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Step 10, after the CPU 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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and then the touch screen can work normally
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These signals are the main working signals of the touch screen
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Let's look at 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_CTS is the touch data clear signal
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When the touch screen does not work,
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invalid data will be cleared and the CPU will be notified
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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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BSYNC is the display touch synchronization signal sent by the display to the touch screen
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In the touch block diagram,
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if one of these signals is abnormal, it will cause no touch failure
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We check the main signals of the touch first
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If there is no problem with the main signals, we will check other detection signals
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That's all for this video
