IPhone 7 won’t turn on  

Максим Исаев
Reading time: 4 min
650

Diagnostics

We were sent a phone for repair from another city with such an issue: iPhone 7 won’t turn on. When connected to USB-tester, the iphone 7 won’t turn on and won’t charge. This heats up the back of the smartphone. We assume there is a short circuit in the board. Repair was carried out during BGA soldering training at a service center.

IPhone 7 won’t turn on

We disassembled the smartphone.

When connected to the LBP and after pressing the power button, the iPhone 7 won’t not turn on and the ammeter showed the presence of a current consumption of 2 Amperes at an operating voltage of 3.8 Volts. And the main power controller iPhone 7 – U1801 was very hot.

Основной контроллер питания IPhone 7
Основной контроллер питания IPhone 7

We assume the presence of a short circuit.

Using an automatic Fluke multimeter, we checked the main power circuits of the phone for the presence of working resistances in them.

We measured the following circuits:

  • PP_BATT_VCC
  • PP_VDD_MAIN
  • PP3V0_NAND
  • PP1V8
  • PP0V9_NAND
  • PP_VDDBOOST

The resistances in the above circuits corresponded to the resistances of the working device.

Since there is no short circuit in the main circuits, and the power controller is heated, it was decided to disassamble the main power controller for further diagnostics.

Since the CPU and Baseband are covered with compound and are located on the reverse side of the Board, opposite the CPU, there are risks to disrupt the soldering of the pins of these chips (overheating of the Board). In order to avoid overheating of the CPU or modem, it was decided to cut down the main power controller on the CNC milling machine.

Замена контроллера питания IPhone 7
Замена контроллера питания IPhone 7

The next step is to prepare the contact area:

  • soldered the contact pad containing lead-free solder with a Rose alloy;
  • collected the remains of solder with a copper braid;
  • removed the remains of the compound.
Контактная площадка
Контактная площадка основного КП IPhone 7

We made measurements using Zillion x Work, namely the voltage drop map on the contact area of the main power controller. To do this, you must put the multimeter in diode dialing mode.

All voltage drops corresponded to the operating values.

The following conclusion can be made: iPhone 7 won’t turn on due to a short circuit in the U1801 chip.

For further repairs, a new controller was purchased. The mandatory procedure is to roll the chip onto lead containing solder.

The next step is to install the chip:

  • in order to avoid overheating, heat sinks were installed;
  • a small amount of Flux Plus flux was applied to the pad;
  • the rolled chip was positioned on the contact pad by key;
  • soldered U1801 with a Quick 857DW + dryer.
Теплоотводы на плате IPhone 7
Теплоотводы на плате IPhone 7

After waiting for the time to lower the temperature, we checked for a short circuit. To do this, we connected the board to the laboratory power supply (LPS) and applied voltage, starting from the minimum acceptable value. No short circuit was detected.

Then we installed the board in the iphone 7 case and turned on the phone from the LPS. The iPhone has successfully turned on, the current consumption corresponds to the operating value.

Then we collected the phone and checked all the functionality. Since everything worked properly, the repair “iphone 7 won’t turn on” – completed.

IPhone 7 не включается
IPhone 7 не включается

Tools and equipment

Used tools and equipment:

  • electronics repair tool kit (screwdrivers, suction Cup, tweezers, showel);
  • separator,
  • USB tester,
  • CNC milling machine,
  • laboratory power supply,
  • hot air soldering station Quick 857D W+,
  • induction soldering iron,
  • multimeter,
  • microscope
  • universal holder the motherboard.

Conclusion

One of the frequent repairs of iPhone 7 is when the phone does not turn on. Most often, the USB controller fails, less often the main power controller. Replacing the U1801 is complicated by the presence of a compound under the chip. And the fact that the main power controller is located directly above the central processing unit (CPU). You can learn how to properly perform such repairs at Bgacenter.

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