How to fix the problem of high startup current of mobile phone？

   In daily life, almost everyone has a mobile phone, and we often encounter the problem that the mobile phone cannot be turned on. There are many reasons why your phone won't turn on. This time, let's take a look at the problem that the iPhone X cannot be turned on due to excessive startup voltage.

   First of all, first check the appearance of the motherboard, the motherboard is not deformed or damaged by water. Then connect the motherboard battery connector to the DC power supply. Start the board with tweezers. The starting current is greater than normal. Judging from this, the fault may be related to the 17 power rails of the PMU output.

   

     We remove the motherboard and need to confirm whether the fault is related to the upper or lower layer. Place the motherboard on a dedicated heating platform. When the platform temperature reaches the set temperature, carefully pick up the upper layer with tweezers. Continue to remove the lower layer from the platform.

    Now we test the upper layer. Connect the battery connector on the upper player to DC power. Activate the upper layer with tweezers. At this time, the starting current is still greater than the normal value. We can now confirm that the failure is related to the upper layer.

   So our next step is to examine the 17 rails of the PMU output. Let's start with PP_CPU_PCORE. Locate the C2701 and make a diode mode measurement of the capacitors on the circuit associated with the C2701. The measured value is normal.

   Continue to measure test points for the remaining 16 rails. From the measured value, PP3V0_NAND has been short-circuited. Since there are many components on PP3V0_NAND, we can locate faulty components by rosin detection.

    Dip some rosin with a 350°C soldering iron. Then smoke rosin on the components on PP3V0_NAND. Set the output voltage of the DC power supply to 3V and ground the black probe. At the same time, touch the red probe with the capacitor on PP3V0_NAND. We can see the rosin on the C2649 melted immediately. Judging from this, C2649 has been damaged. Let's try to detach the C2649 from the board.

   Let's try removing the C2649 from the board and see how it works. First remove the black adhesive around the C2649. Then we can gently remove it with tweezers. Ground the red probe again. Touch the two pins of the C2649 with the black probes. The measured value is normal. We can now confirm that the short circuit condition was caused by a damaged C2649.

   However, we need to test the upper layers. Remove top layer and clean with PCB Cleaner. Connect the upper battery connector to the DC power supply. Start the upper layer with tweezers. The boot current is normal this time.

   Now we solder the two layers together and install the display components. Connect the battery connector to the DC power supply and boot the board with tweezers. The starting current is normal. The mobile phone comes with a normal display and can access the system. Fault cleared.

   According to the above description, we can solve the problem that the iPhone X cannot be turned on due to excessive starting current. If you need mobile phone repair tools, you can open our China Phonefix Shop and see above.