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This lesson talks about how to analyze the abnormal ground value of the power supply

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when measuring the touch connector

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When the ground value of the touch power supply is short-circuited,

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that is, the multimeter shows 0,

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how should we repair it at this time?

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Take Xiaomi 11 as an example

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This is the 1.8 V power supply of the touch, which goes to pin 57 of the connector

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This is the touch connector number

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switch to bitmap

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In the bitmap, pin 57 of the connector is the 1.8 V power supply

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When measuring this point, there is a short circuit in the power supply,

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how do we proceed to the next step of maintenance

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Click the left mouse button on pin 57,

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you can see that one end of it is connected with the capacitor C6511

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We don't consider the side connected to the resistor

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Because these two resistors are pull-up resistors, short circuits have nothing to do with them

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There is also a capacitor connected to the 1.8V power supply line at this position

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Since this capacitor has a ground pin on one end,

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we have to take that into account as well

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Let's continue to see where this 1.8V leads

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It goes to the chip U4700

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Because the chip U4700 has a ground pin, so this chip should also be considered

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let's sum it up

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There is a short circuit in this line, we only consider the components that are grounded at one end

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Just now we found that there are two capacitors, one chip, and two resistors grounded at one end

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Both of these resistors are over 1,000 ohms, but pull-up resistors,

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the other end of them is not grounded, the short circuit has nothing to do with them

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It is only related to these two capacitors and a chip

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How can we repair it after analysis?

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Every time a component is removed, measure the ground value on the pin 57 of the connector

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When a component is removed, the ground value returns to more than 500,

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indicating that the line is repaired,

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and it also means that the capacitor we removed caused a short circuit in the line

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this is a situation

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In another situation, when we remove a capacitor, the ground value of pin 57 is still 0,

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and we need to continue to take another capacitor

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After removing the capacitor, measure pin 57 again

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If the ground value is still 0, we need to remove the chip U4700 and re-solder

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If after re-soldering, the ground value of pin 57 is still 0, then replace the chip U4700

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This is the analysis and repair of power supply short circuit

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That's all for this lesson