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This lesson talks about how to analyze when the ground value of the I2C bus on the touch connector is OL

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Take Xiaomi mobile phone as an example, open the schematic diagram and bitmap of Xiaomi 10 Pro

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Enter the touch code TP_I2C in the schematic diagram

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not found

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Let's try searching for TS_I2C

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The I2C bus for touch is this one

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This is the serial clock of the I2C bus, you can find the touch connector through here

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This is the connector for touch and display, J6400

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The I2C bus of the touch has two lines,

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one is the serial clock SCL, and the other is the serial data SDA

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Switch to bitmap

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Right-click and select Find Bitmap Signal

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In the bitmap, the chip U3100 lights up, this chip is the CPU,

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and the connector J6400 lights up at the same time

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Zooming in, we found that the I2C bus clock pin is on the pin 12 of the touch connector

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Left click on pin 12, TS_I2C_SCL appears here on the lower right pin

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It goes to the CPU and also to the resistor R3217

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The other end of the resistor is connected to the 1.8 V power supply

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One end is the power supply and the other end is the I2C signal

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This resistor is called a pull-up resistor

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This is the clock pin of the I2C bus

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There is another line of the I2C bus on the pin 10 of the connector,

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TS_I2C_SDA, which is the data pin

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Let's take a look at the components connected to the data pin

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One is the connector, the other is the resistor R3216

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The other pin of the resistor is powered by 1.8 V, it is also a pull-up resistor

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Let鈥檚 continue searching

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The data pin of the I2C bus also goes to the H36 pin of the CPU U3100

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This is the channel of the I2C line

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In the maintenance, the measurement method of these two wires is the same,

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we take one of the wires as an example to analyze

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When it is measured that the ground value of pin 12 is infinite,

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it is related to the connector and the CPU

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The pull-up resistor will not affect its ground value, so it is not considered

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Maintenance steps

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First observe whether the connector is falsely welded

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If it has been soldered falsely or there is water corrosion, we re-solder the connector

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If it still doesn't work after re-soldering, then we need to replace the connector

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Another situation is that the connector has no water corrosion,

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has not been moved, and has not been deformed or damaged

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At this time, it is difficult to handle

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We have to re-solder the CPU and measure the ground value again

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If the ground value is still infinite, remove the CPU,

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solder a wire from the corresponding pin of the CPU,

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and connect it to the pin of the connector, and the fault can be repaired

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That's all for this lesson