If your iphone don't have the function of calling, Maybe you will be crazy. Verbal communication is one of the most basic necessities of any phone user. If this requirement is not fulfilled, any user maybe give up it. If you are using the iPhone, you will experience this issue like no sound. When you face this problem, you can send it to Apple Store.

The customer bought a new iPhone 6S. After activating it, he was downloading ringtones through i4 assistance when a call came in. Then the new iPhone rebooted itself and had no handfree sound. The customer did not want to wait for a changed iPhone, so he has had it fixed in many places. However, the problems still exist.

First, After tearing down, we find that the audio amplifier chip and vibration control chip has been moved. Because the two chips are of the same type, the previous maintenance personnel might not know which one was audio amplifier chip. The material object of amplifier chip and vibration control chip are shown in picture 1-1. In fact, U3800 is used to drive the vibrator and U3700 is used by the audio amplifier chip to drive speaker. As the two chips are of the same type, they can be exchanged with each other as well as with that of iPhone 6.

Second, Tear down the audio amplifier chip U3700 bus and measure the diode data to ground of power supply and of the bus runs toward CPU. The data is normal. But the the diode data of pin A2 connected to boost inductor L3700 is 550 higher than the normal about 330 which is the same as that of main power supply PC_VCC_MAIN.

Third, The diode data between L3700 and pin A2 is about 200. Based on the circuit principles, the diode data of the two pins should be the same. We cannot figure out where does the additional 200 come from. Jump a wire from the pin 2 of L3700 to the pin A2 of U3700, as shown in picture 1-2. Then, assemble audio amplifier chip to iPhone and turn on. After entering IOS and testing, iPhone 6S has no sound when press the handfree button.

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