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Introduzione

iPhone 6 keeps searching for signal? Causes can be different and solutions flexible. Replace with a new SIM card? Restart your phone? Or reset the network? If the problem has been fixed, well, congratulations! If not, you may be interested in our chip level solution regarding to the ‘Searching’ issue caused by power amplifier IC.

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  1. Signal bars in the upper-left corner have been replaced by ‘Searching…’. Go to Settings>General>About. Normal ICCID, which indicates that SIM card can be read. IMEI, MEID and Modem Firmware are also normal. Which indicates that baseband circuit is in normal state.
    • Signal bars in the upper-left corner have been replaced by ‘Searching…’. Go to Settings>General>About. Normal ICCID, which indicates that SIM card can be read.

    • IMEI, MEID and Modem Firmware are also normal. Which indicates that baseband circuit is in normal state.

    • Judging from this, the searching issue has something to do with radio-frequency circuit.

  2. Let’s begin with measurement of RF circuit power supply voltage. Go with one set of voltage first, PP_LDO8 2V0. Measure the voltage value of corresponding capacitor, C3801. The voltage value is 2V0, which is normal.
    • Let’s begin with measurement of RF circuit power supply voltage.

    • Go with one set of voltage first, PP_LDO8 2V0. Measure the voltage value of corresponding capacitor, C3801. The voltage value is 2V0, which is normal.

    • Then the second set of voltage, PP_LDO1 1V3. The voltage value of corresponding capacitor C3808 is 1V3, which is normal. The third set of voltage, PP_LDO11 1V8 is also normal.

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  4. Next, let’s continue with the signal amplifier power supply voltage, VPA_APT. Measure the voltage value of corresponding capacitor, C4108. There is no voltage value. Normal voltage value should be 3V7.
    • Next, let’s continue with the signal amplifier power supply voltage, VPA_APT. Measure the voltage value of corresponding capacitor, C4108. There is no voltage value. Normal voltage value should be 3V7.

  5. C4108 3V7 voltage is outputted by U_QPOET. Yet U_QPOET 4V2 voltage is inputted from L4001-RF.
    • C4108 3V7 voltage is outputted by U_QPOET. Yet U_QPOET 4V2 voltage is inputted from L4001-RF.

    • Measure the voltage of L4001-RF. The voltage value is 4V2, which is normal. We can conclude that U_QPOET broke down, which resulted in abnormal value of VPA_APT 3V7.

  6. So we need to replace with a new U_QPOET. Apply some BGA Paste Flux around U_QPOET. Then take down the IC with Hot Air Gun. Once the IC has been removed successfully, clean the bonding pad with Soldering Iron.
    • So we need to replace with a new U_QPOET.

    • Apply some BGA Paste Flux around U_QPOET. Then take down the IC with Hot Air Gun. Once the IC has been removed successfully, clean the bonding pad with Soldering Iron.

    • Apply some BGA Paste Flux to the bonding pad. Align the new IC to the right place. Solder the new IC with Hot Air Gun.

  7. Get the logic board assembled and connect the battery. Buckle the display assembly and insert SIM card. Power on and test.
    • Get the logic board assembled and connect the battery. Buckle the display assembly and insert SIM card. Power on and test.

    • Signal bars in the upper-left corner are back to normal. Make a phone call, the talk getting through normally. Fault cleared.

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Phryne

Membro da: 17/11/2019

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