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In this lesson, let's learn the maintenance steps of no touch faults

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When the ground value of the power supply is measured to be normal,

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it is necessary to measure the next working condition of the touch,

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that is, the ground value of the reset signal

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If there is infinity in the ground value, how should we analyze it?

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Take Xiaomi 11 as an example

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Open the schematic diagram

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TS is touch, RESET is reset

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This line is touch reset

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It goes to the pin 45 of the touch connector

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We switch to bitmap

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Double-click the left mouse utton to select the position number J6503 of the touch connector

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Right-click and click find the bitmap component, so you can find the touch connector

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This is the bitmap, the connector on the actual mainboard is here

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Pin 45 is the touch reset signal, let's take a look at its circuit

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There is a capacitor connected to this line, let's ignore it

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we continue to search

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There is a pull-up resistor here, which is powered by VREG_L2C_1P8 to provide pull-up

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we continue to search

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It goes to pin C28 of CPU U3100

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By learning the diagram, we know that there is a capacitor, a pull-up resistor, a CPU,

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and a connector J6503 on this line,

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a total of four components

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During maintenance, when the reset signal of pin 45 is detected as OL,

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we first check whether the connector has been soldered

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If the connector has been soldered falsely, just re-solder it,

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it will return to normal, and the fault can be repaired

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If the connector has not been soldered falsely, we measured its ground value is OL

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Because this line only connects to the pins of the CPU, it is difficult to handle at this time

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Remove the CPU, re-solder it

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After soldering, if it is still infinity,

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either the CPU is damaged, or the board is broken

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CPU damage is irreparable

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If the CPU is not damaged, remove the CPU

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One marker of the multimeter is placed at the corresponding point on the CPU,

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and one marker is placed at pin 45 to measure the continuity of the circuit.

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If the line is connected, it proves that the CPU is broken

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If it is OL between these two points, we can use the method of flying wire to solve the fault

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These are the repair steps when the reset signal value is infinite

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That's all for this lesson