Two Steps for iPhone 7 turning on failure

Usually when we met the iPhone 7 turning on failure ,we will do it by individ two steps, one for the surface ,one for motherboard, then we can find the sources fault and solve it totally, okay, let us start our first step.

• Step One: Dignosing

1. Disassemble the iPhone 7 and disconnect the battery
2. Connect the iPhone 7 to the DC power Tsupply, it reads and stops at 350mA, which is abnormal, indicating that the iPhone 7 circuit board is short circuited.
3. Disconnect the power supply and take out the logic board. Run diode measurements on capacitors around power IC one by one. All the values are normal except  C1823 – It displays 0, which indicates that C1823 is short-circuited. From the schematics, we can see that C1823 is the filter capacitor of PP1V8-SDRAM, and it is directly connected to CPU SDRAM.
4. Disconnect the DC power supply and take out the iPhone 7 circuit board.
5. Measure diode on capacitors around iPhone 7 power IC one by one. Besides c1823 shows 0, all values are normal, which indicates c1823 short circuit. 
6. From the WUXINJI schematic diagram, we can see that c1823 is a pp1v8-sdram filter capacitor, which is directly connected to the iPhone 7 CPU, SDRAM.

What the above step is dignosing step, we can know the fault value and where happens the fault, the next we will disassemble it and fix it.

• Step Two: Repairing

1. Put the iPhone 7 motherboard to PCB repair holder, heat the shield cover with QUICK 861DW hot air rework station.
2. Use CNC chip grinding machine to remove the CPU SDRAM. 
3. After grinding, Put iPhone 7 motherboard to PCB holder and clean with a PCB cleaner, remove the black adhesive with knife. 
4. Apply some BGA solder paste to the weld plate. Align the new SDRAM to the right position, and then weld it with a hot air gun. 
5. After cooling for 5 minutes, clean thoroughly with PCB cleaner.
6 Connect iPhone 7 with DC Power Supply
7 Use a precision tweezer to trigger the power on system by shorting the Pin 13 of J4504 to the ground. the current should be normal this time.
8  Assemble the iPhone 7 motherboard and buckle the display assembly. 
9 Connect iPhone 7 to the computer, then press the power button and volume down at the same time to enter into DFU mode. 
10 Restore the iPhone via iTunes, then insert the SIM card and activate the iPhone 7.

One fault , One solution, no matter which fault occurred,there must exist a solution way, just be patience for this, don't drag it ,throw it. Or you can contact us, learning always is a interesting thing.