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iPhone X Won’t Turn On – Large Boot Current Repair

Our previous blog has walked you through the work-flow of iPhone X Boot Circuit. And you have learned that to have the phone turned on, working conditions like power supply, clock signal and reset signal are indispensable. Since there are so many components involved in the process, reasons for won’t turn on of the phone can also be various.

Today we will explain the troubleshooting and repairing process of iPhone X by showing a real-life iPhone X won’t turn on case. Follow our repair guide step and step and you can definitely learn something.

Analyzing 

First, run cosmetic inspection of the motherboard. The motherboard is not deformed or water damaged.

Then connect the motherboard with the DC power supply. We can see that there is no current leakage. Judging by this, the three main power supply rails, PP_BATT_VCC, PP_VDD_MAIN and PP_VDD_BOOST are in normal condition.

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Continue to get the motherboard booted up with tweezers. We can see that the boot current is larger than normal value. We can confirm now that the fault is probably related to the 17 power supply rails outputted from PMU.

Motherboard Separating

Now we need to separate the motherboard to confirm whether the fault is related to the upper layer or the lower layer.

Place the motherboard on the specialized Heating Platform. With temperature of the platform reaching the set temperature, pick up the upper layer with tweezers carefully. Continue to take the lower layer off the platform.

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Diagnosis

Now we can test the upper layer. Connect the battery connector on the upper player with the DC power supply. Then get the upper layer booted up with tweezers. The boot current is still larger than normal value. We can confirm now that the fault is related to the upper layer.

iphone-x-wont-turn-on-large-boot-current-repair

So our next step is to check the 17 rails outputted from PMU one by one.

Let’s start with PP_CPU_PCORE first. Locate C2701, one of the test points of PP_CPU_PCORE on Refox. Then run diode mode measurement of a capacitor on C2701 relevant circuit. The measured value is normal.

iphone-x-wont-turn-on-large-boot-current-repair

Continue measuring test points of the remaining 16 rails. Judging by the measured value, PP3V0_NAND has shorted. Since there are many components on PP3V0_NAND, we can locate the faulty component with rosin detecting.

Dip some rosin with the Soldering Iron at 350℃. Then smoke rosin on components on PP3V0_NAND. Set the output voltage of the DC Power Supply at 3V. Get the black probe grounded. Meanwhile, get the red probe touched with a capacitor on PP3V0_NAND.

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We can see that rosin on C2649 melts immediately. Judging by this, C2649 has been damaged.

Troubleshooting

Let’s try to detach C2649 from the board and see how it works.

Remove black adhesive around C2649 first. Then we can just remove it with tweezers slightly.

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Again, get the red probe grounded. Touch the two pins of C2649 with the black probe. The measured value is normal. We can confirm now that the shorted condition is caused by damage of C2649.

Still, we need to test the upper layer. Remove the upper layer and clean with PCB Cleaner. Connect the battery connector on the upper layer with the DC Power Supply. Get the upper layer booted up with tweezers. The boot current is normal this time.

iphone-x-wont-turn-on-large-boot-current-repair

Motherboard Recombining

Next thing we need to do is to solder the two layers together.

Remove heat insulation adhesive on the lower layer first. Then place the lower layer onto the heating platform. Power on the heating platform and apply some Paste Flux to the third space PCB. Then get the upper layer in position.

iphone-x-wont-turn-on-large-boot-current-repair

Reassemble And Test

Get the display assembly installed. Connect the battery connector with the DC Power Supply and get the motherboard booted up with tweezers. The boot current is normal. The phone comes with normal display and can get access to the system. 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 X step by step.

When repairing iPhone logic boards, we identify the issue first, find out why it occurred next, and figure out how to fix it in the end. This is a general process adopted by professional repair technicians around the world.

Wanna be a professional repair technician and handle iPhone tough repair? You need systematic training courses on REWA Academy.

Just click the course link below to know more!

 

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