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iPhone 6 Series Repair

iPhone 6 Keeps Searching For Signal – Logic Board Repair

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.

Problem 

Power on. Signal bars in the upper-left corner have been replaced by ‘Searching…’.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.

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

Diagnosis 

Let’s begin with measurement of RF circuit power supply voltage.

Disassemble the phone and take out the SIM card, then logic board. Attach the logic board to PCB Holder. Take down the shield plate with Hot Air Gun first.

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Run cosmetic inspection, no water damage or mouldy condition.

Next thing we do is to re-insert SIM card and connect the logic board with DC Power Supply. Connect Pin 2 of J0801 with negative point on logic board by tweezers to power on.

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Run RF circuit power supply voltage measurement. 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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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.

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

U_QPOET is located under shield plate on the other side of logic board. Welded junctions of the shield plate come with high melting point. To protect components around from high temperature, we can remove the shield plate with Cutting Nipper.

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Once finished, run cosmetic inspection. No water damage or mouldy condition. Connect the logic board with DC Power Supply. Connect Pin 2 of J0801 with negative point on logic board by tweezers to power on.

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.

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Troubleshooting

So we need to replace with a new U_QPOET.

Attach the logic board to PCB Holder. Apply some BGA Paste Flux around U_QPOET. Then take down the IC with Hot Air Gun at 320℃.

Once the IC has been removed successfully, clean the bonding pad with Soldering Iron.

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Also when cleaning, add low melting point solder paste to the bonding pad with Soldering Iron. Which is helpful to the subsequent removal of solder.

Once done, clean again with PCB cleaner. Apply some BGA Paste Flux to the bonding pad. Align the new IC to the right place (don’t reverse the direction). Solder the new IC with Hot Air Gun at 320℃.

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Once the soldering process is finished, wait for the logic board to cool for 5 minutes. Then clean with PCB Cleaner.

Reassemble 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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Tools Used

Visit our online shop for more parts and tools.

You can also visit REWA YouTube Channel to check our video and learn how to repair the iPhone 6 searching issue step by step.

More about iPhone 6 repair

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