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Tuesday 07 January, 2020 |

Liquid damaged iPhone 7 without 4G Signal- how to fix?

Some liquid goes into the iPhone 7, the iPhone 7 can still be turned on, unfortunately, the iPhone 7 4G signal is missing. When the SIM card is inserted, the iPhone 7 has no 4G signal and only 2G. Restart the iPhone 7, the iPhone 7 4G failure is still exists, mostly it's cause by hardware error.

The iPhone 7 2G signal is normal, but no 4G signal, which means there is problem with the 4G signal part; and this problem came out after the liquid entered the iPhone, so we suspected that the liquid had damaged the 4G signal circuit channel.

Use Phonefix screwdriver to remove the screws next the iPhone lightning port, put the iPhone 7 on the CPB screen separator, and then use screen sucker to open the iPhone 7.

Remove the iPhone 7 display assembly, disconnect the iPhone battery, and then take off the iPhone 7 motherboard.

Put iPhone motherboard under a microscope to observe, all looks normal.

Place the iPhone motherboard to PCB holder fixture, and then use hot air gun and tweezers to remove the 4G amplifier chip.

After the TDDPA_RF 4G amplifier IC was removed, use Fluke 17B+ digital multimeter to measure the grounding resistance value of the solder pad, and we found that the 11 Pin MLB_VBATT value is infinity, it should be the circuit disconnected.

Log in to the WUXINJI online account to check iPhone 7 schematic diagram, we found this voltage to TDDPA_RF,MLBPA_RF these 2 chips, and MLBPA_RF IC not installed.

This voltage is renamed to MLB_PA_VBATT after the PP_PA_VBATT passes through the R7113_RF resistor, observe it under the microscope, we found the R7113_RF resistor had been corroded.

Look at the iPhone 7 schematic diagram, it's 0 euro resistor. Use JBC CD-2SHE soldering station to short connect a jump wire to it directly, and then use digital multimeter to measure it again, the data measure is normal.

Weld the 4G amplifier chip to the motherboard, and then assemble the iPhone 7.

Insert the SIM card; turn on the iPhone 7, now the 4G signal is back to normal, the iPhone 7 4G failure has been fixed!

by Bellin

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