In the first case, the volume of the mobile phone does not turn on. The solution: try to dial a phone number, and press the volume button on the side of the fuselage to raise the sound when dialing or talking.
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In the second case, the volume of the car navigator does not turn on, just turn it on.
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The third situation: Go to Settings-Sound, find the media option, and turn up the media volume.
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Bluetooth is a wireless technical standard, which can realize short-distance data exchange between fixed equipment, mobile equipment and personal area network of buildings.
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Bluetooth technology was first invented by telecom giants in 1994 as a substitute for RS232 data line.