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Usage of multimeter

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In this lesson we mainly learn how to measure circuit board voltage

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Measuring voltage is an essential maintenance step in maintenance,

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we can judge whether the line is normal according to the voltage value

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When repairing the mainboard of the mobile phone, the voltage of the mainboard is DC

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Method of Measuring DC Voltage

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In the first step, the black marker of the multimeter is inserted into the public port,

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and the red marker is inserted into the red socket marked by the voltage resistance

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The second step is to adjust the multimeter to the DC voltage range

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If it is a manual range multimeter, we need to choose the 20V DC voltage range,

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because the power supply of the mobile phone is 4.2V

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If it is in the 2V position, the voltage value cannot be measured

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The mainboard needs to be powered on when measuring the voltage,

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and some power supplies need to be triggered to start up when measuring the voltage

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After measurement, the value displayed on the screen is the voltage value

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Precautions when measuring

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When measuring the voltage, the mainboard must be powered on

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If it is a manual range multimeter, select the appropriate range,

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and the range should be greater than the voltage of the point to be measured

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When measuring, the markers cannot be reversed.

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After the reverse connection, there will be a minus sign in front of the measured voltage,

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which is generally called negative voltage

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There is a negative voltage in the mobile phone,

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and the measurement after reverse connection may lead to misjudgment

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Let's measure it in the physical mainboard

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First, we insert the black marker into the COM port,

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and the red marker into the V red port

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The multimeter is adjusted to the DC voltage range,

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and the mainboard needs to be powered on when measuring, or trigger the power on

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After we trigger the switch, the black marker is grounded,

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such as a metal shell or a screw post,

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and then the red marker is used to measure

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At this time we can see that the voltage value is about 1.2V

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After changing the measurement point, we can see that the voltage is about 0.8V

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If the red marker is grounded, the black marker is used to measure

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We can see that the display will show about -4.2V

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The 1.2V power supply measured just now supplies power to the hard disk

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If the voltage is lower than 1.2V or higher than 1.2V,

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it means that there is a problem with the power supply

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That's all for this video