It is really annoying when your iPhone won’t turn on. This is even worse when you can’t find out the problems and solve it. In today’s guide, we are going to show you the complete solution on how to troubleshoot and repair iPhone won’t turn on. It doesn’t matter whether:
- The iPhone won’t turn on after dropped into water.
- The iPhone won’t turn on after the storage expansion of hard disk
- The iPhone won’t turn on with starting current 70mA and starting current jump repeatedly
You don’t have to worry so much about this. Just read through this guide to solve any of these problems. It is simple and straightforward:
Example of iPhone 6 Won’t Turn On Problems 1 :
Regulated power supply of iPhone 6 shows the current of 70mA, but it could not be turned on.
iPhone 6 Won’t Turn On Failure Phenomenon 1 :
After the triggering, Starting current is 70mA, and the customer had used iTunes To restore the phone, but failed, showing an error of 4014.
iPhone 6 Won’t Turn On Maintenance Procedures 1 :
For this motherboard, the customer heated the CPU with an air gun by himself. Error 4014 is reported when the phone is in the recovery.Generally speaking, the reporting of error 4014, occurs because of problem of the CPU, temporary storage or power supply. After removing the motherboard, some traces of corrosion around the U1400 shield of the motor driver chip were found, as shown in Pic 5-41.
The corrosion around the U1400 shield of the motor driver chip is shown in Pic 5-41.
Removing the shield, and the corrosion of U1400 could be found. The enlarged corrosion surrounding motor-driver chip is shown in Pic 5-42.
The corrosion of motor-driver chip U1400 is shown in Pic 5-42.
Cleaned the corrosion and the phone could be opened normally after the replacement of a U1400 chip. The position of the motor driver chip U1400 in the bitmap is shown in Pic 5-43.
The position of the motor driver chip U1400 in the bitmap is shown in Pic 5-43.
This problem was the bad performance of I2C bus caused by U1400 damage, resulting in the reporting of error 4014 when flashing.
Example of iPhone 6 Won’t Turn On Problems 2 :
iPhone 6 could not be turned on, stabilized power supply jumped at110mA and 130mA
iPhone 6 Won’t Turn On Failure Phenomenon 2 :
A phone that has short circuit caused by water inlet, after removing several capacitors, the leakage current was 200mA. After replacing power supply chip U201, no leakage occurred, but it could not be turned on and the current was repeatedly beat at 110mA and 130mA.
iPhone 6 Won’t Turn On Maintenance Procedures 2 :
Most of this situation is the circuit fault of the touch chip U4202, the power supply chip U1202, and the upper layer of the CPU temporary storage. The customer replaced the power chip before, therefore, replace the power chip first to eliminate soldering problems by the customer. After replacing the power chip, the current at switching on was the same as 110mA, 130mA. According to the maintenance experience, For the water damaged iPhone, the damage of upper-layer of the temporary storage is mostly caused by the short circuit of the chipset itself. Observed the surrounding places of the temporary storage and the CPU with a microscope and found that there was a soldering ball surrounding the upper- layer temporary storage. The iPhone switched on normally after removing and reinstalling the upper-layer temporary storage. The soldering ball surrounding temporary storage was shown in Pic 5-44.
The soldering ball surrounding temporary storage was shown in Pic 5-44.
When this machine was of maintenance, the CPU shield cover had not been touched, so whether there were soldering balls was not checked first. For the main board of the chip behind the CPU touched by other maintenance staffs, it was better to check whether there was soldering ball on the CPU and the upper-layer temporary storage chip of the CPU.
Example of iPhone 6 Won’t Turn On Problems 3 :
iPhone 6 won’t turn on and lead to current leakage 60mA after it dropped into water
iPhone 6 Won’t Turn On Failure Phenomenon 3 :
The phone could not be switched on after it dropped into water.
iPhone 6 Won’t Turn On Maintenance Procedures 3:
After removing the screen and battery, connect the phone with the adjustable power supply to power up the motherboard, with the current of 60mA shown. After pressed the switch-on button, the current stopped at 120mA. After removing all shielding covers, some of the filter capacitors of the main power supply of PP_VCC_MAIN were blackened.
According to the circuit principle, it should be first determined whether the leakage was from of the circuit of battery power supply PP_BATT_VCC or from the circuit of the main power supply PP_VCC_MAIN. Therefore, we removed the Q1403 field effect transistor which was responsible for converting battery power supply to main power supply. The Q1403 in the bitmap as shown in Pic 5-45.
The Q1403 field effect transistor in the bitmap as shown in Pic 5-45.
If the battery still showed leakage after removing the Q1403 and connecting the adjustable power supply, it could deduce that the circuit of the battery-powered PP_BATT_VCC existed leakage, otherwise, the circuit of the main power supply PP_VCC_MAIN existed leakage.The power supply showed no leakage by electricity test. According to the maintenance experience, the Water damaged phone first should be considered the power supply IC, the backlight IC, the large power supply and the capacitors. (the leakage of filter capacitor on the main power supply PP_VCC_MAIN line would not cause the switch-on failure basically).
After loading the Q1403, the components around the display power supply chip U1501 and the backlight chip U1502 were smoked with a thin layer of resin and then checked whether the heating element could be found by an electric test. The display power supply chip and backlight power supply chip smoked with rosin were shown in Pic 5-46.
The display power supply chip and backlight power supply chip smoked with rosin were shown in Pic 5-46.
After a few minutes of electricity, it was found that the location of fumed rosin basically showed no response. If the leakage was caused by the capacitor, the functional chip and the part of the chip of baseband could be first repaired, and checked the function after the switch-on, then went back to block the rough fault range through the failure of the functional module circuit. The current on this main board of 120mA subtracts the leakage of 60mA, leading to the rough current of about 50~-60mA after the switch-on of the phone, which was basically caused by the working condition of the CPU, the damage of circuit of I2C0 bus, the I2C1 bus, the large power supply chip U120 and so on.
Measured all the power supply of CPU by electricity, all the power supply voltages were normal except PP_GPU voltage (which could be measured only after the normal switch-on), and then the AP_TO_I2C0_SCL voltage was found to be only about 0.3V for the second measurement of the 12C bus. This phenomenon could be basically judged by measuring the resistance value to ground. Generally speaking, it is the problem of pull-up resistor and CPU when there is high resistance value to the ground and low voltage of 12c bus. When the Ground impedance values were pulled down or short-circuited, it could only be judged by removing the connected chip. The I2C0 bus circuit could be measured on resistors RO302 and RO303. The pull-up resistor RO302 and RO303 on the I2C0 bus in the bitmap are shown in Pic 5-47.
The pull-up resistor RO302 and RO303 on the I2C0 bus in the bitmap are shown in Pic 5-47.
The Ground impedance values of AP_TO_I2C0_SCL for power-down measurement was only 33. I2C0 bus to CPU, display power supply IC, backlight power supply IC, USB chip, large power supply.The I2C0 bus usually is pulled down by the display IC and USB chip after dropping into the water. First removed the display power UI501 and then tested with power, which turns out no leakage found. Short connected the switch-on to find that the adjustable power supply could go to about 1A. After the current jumped normal, the phone could be switched on normally. Removed a U1501 display power chip from the material board and installed it on the faulty board. After the power on, The screen displayed normally after showing the Apple logo. Pic 5-48 shows the position of the power supply chip U1501 in the bitmap.
The position of the power supply chip U1501 in the bitmap is shown in Pic 5-48.
For the fault of current leakage and failure of power on, we could directly fix the failure of power on first if we could not found out the reason for the heating. Usually after the failure of switch-on is repaired, the other faults disappeared, or Usually after the failure of switch-on is repaired, although the function is still problematic, the point of failure could basically be found when entering all the functions of the system test.
Example of iPhone 6S Won’t Turn On Problems 4 :
The iPhone 6S won’t turn on after dropped into water and the power failed repeatedly after the stabilized voltage shows 50mA
iPhone 6S Won’t Turn On Failure Phenomenon 4 :
The customer described that the phone could not be turned on after dropping into water, and it was opened and cleaned by himself. The CPU upper cover had already bulged.
iPhone 6S Won’t Turn On Maintenance Procedures 4 :
Disassembled the iPhone and connected the main board to the adjustable power supply, only to find that there was no current in the state of power-on. It could be determined that the main power supply was of no short circuit. Triggered the boot, the current jumped to 50mA and power failed, and then automatically powered up to 50mA, but power failed again and repeated the above process.
If there was a short circuit in the voltage output from the power chip of iPhone 6S, the chip would enter the protection state. Therefore, The ground impedance value of the power supply on the upper cover of the CPU was measured first, and no short circuit was found. Then we measured the body-diode value of each power supply, as shown in Pic 5-1. When the voltage of the hard disk p3v0-NAND was measured, it was found that it ground impedance values was 0, which was determined as a short circuit.
Pic 5-1 The Test result of the hard disk power supply short-circuit
The location of this voltage measurement point of p3v0-NAND in the bitmap is shown in Pic 5-2. The physical location is shown in Pic 5-3.
Pic 5-2 The location of the measurement point of p3v0-NAND in the bitmap
Pic 5-3 The physical location of the measurement point of p3v0-NAND on the motherboard
Observed under the microscope, it was found that there was a trace of black corrosion on one end of a capacitor, which is shown in Pic 5-4.
Pic 5-4 Black corrosion of the capacitor
Checked the bitmap and found out the position number of this capacitor as C1503 as shown in Pic 5-5. This capacitor was the power supply filter capacitor of the hard disk. The relevant circuit of the C1503 capacitor is shown in Pic 5-6.
Pic 5-5 The C1503 capacitor in the bitmap
Pic 5-6 The relevant circuit of the C1503 capacitor
Example of iPhone 6S Won’t Turn On Problems 5 :
After the iPhone6S dropped into water, the starting current jump between 0mA and 120mArepeatedly.
iPhone 6S Won’t Turn On Failure Phenomenon 5 :
After the phone dropped into the sea, the screen flashes a few times and turned into the dark when pressed the power button, then the phone could not be turned on anymore.
iPhone 6S Won’t Turn On Maintenance Procedures 5 :
Connected to the adjustable power supply and check the current, and it showed a leakage of 60mA, however, jumped to 120mA after pressing the power button, and then jumped back to 0 mA, with the cycle repeating.
First removed the shield cover of the CPU and baseband, and found that there were four main locations for corrosion: backlight power supply chip U4020, display power supply chip U4000, charge management chip U2300, and small audio core U3700. If repairs the water damaged the phone, generally takes photos of the places for water-inlet first and then cleans the main board, which could help to find problems in the Maintenance procedure by referring to the pictures, and the severely corroded components could be eliminated first.
Connected the power after the cleaning, it was found that the leakage current was reduced to about 20mA. The current jumped between 70mA and 0mA repeatedly after the phone was switched on. Measured the power supply voltage of CPU U0600, and no abnormality found, but when measured voltage of I2C bus, it was found that the signal of I2C0_AP_SCL had only 1.1 V voltage. The position of the 12C0 bus in the circuit diagram is shown in Pic 5-55. The measurement position of the 12C0 bus in the bitmap is shown in Pic 5-56. The physical measurement position of the 12C0 bus is shown in Pic 5-57.
Pic 5-55 The position of the 12C0 bus in the circuit diagram
Pic 5-56 The measurement position of the I2CO bus in the bitmap
Pic 5-57 The physical measurement position of the I2CO bus
The ground impedance values of the I2C bus measured on power-off were 404 and 430 respectively which were within the normal range. Looked at the picture of corrosion, it felt that the power supply chip was damaged, because the backlight chip was glued which was not easy to be eroded, therefore, directly removed the power supply chip U4000.
It showed the same current when powered on after the power supply chip U4000 was removed, but the I2CO bus voltage becomes normal. The failure should be caused by the power supply chip U2000 and the backlight chip U4020. The failure of switch-on phenomenon caused by the backlight U4020 should be related to two sets of signals. One was the I2CO bus, and the other was the backlight brightness adjustment signal, that was, the DWI bus of the backlight chip, which was connected to the power supply and the CPU. The position of the backlight DWl bus interface in the circuit diagram is shown in Pic 5-58.
Pic 5-58 The position of the backlight DWl bus interface in the circuit diagram
There are two signal lines of SDI and SCK on the backlight DWI bus. Judged whether the backlight chip U4020 was good or not by measuring the ground impedance values. The SCK could be measured directly on the resistor R4020 shown in Pic 5-59. SDI could be measured at the test point PP1002 shown in Pic 5-60.
Pic 5-59 The resistor R4020 in the bitmap
Pic 5-60 The test point PP1002 of the signal of backlight DWI bus in the bitmap
It was found that there was short-circuit when measuring the ground impedance values of R4020. Directly removed the back-light chip U4020, then powered on the motherboard, the current run to 1A or more. The phone could normally go into the system after installing the backlight chip U4020 and the display power supply chip U4000.
When repairing the water damaged phone, the removed chip which it doesn’t affect the switch-on could not be installed first. If the current could jump normally, then return the chip.
Example of iPhone 6S Plus Won’t Turn On Problems 6 :
iPhone 6S Plus could not be switched on after expansion of hard disk, and current drops from 100mA to 0mA
iPhone 6S Plus Won’t Turn On Failure Phenomenon 6 :
After the expansion of the hard disk, the phone cannot be turned on. The current reach to 100mA when pressing the power button.
iPhone 6S Plus Won’t Turn On Maintenance Procedures 6 :
Connected to the adjustable power supply test, the power supply reached directly up to 100mA after switching on but jumps to 0mA after 2s.
Taking into account the occurrence of the failure after the expansion, therefore, check whether there was soldering ball surrounding the CPU first. After removing the shielded iron above the CPU, it was found that the upper layer of the CPU was slightly bulging which was not obvious. Under the microscope, no soldering ball surrounding the CPU was found.
Directly short connect the power supply of the hard disk PP3V0_NAND according to the method shown in Pic 5-49, forcibly enter the DFU mode to see if the motherboard could be connected (a lot of power-off motherboards will not be powered down as long as they could force into DFU).
Pic 5-49 The capacitors C1501 for the short-circuiting of the hard disk 3v power supply
Connected the power supply and the tail plug, and Short connected the non-grounded end of the capacitor C1501 on hard disk power supply PP3V0_NAND with tweezers to the surface of the hard disk (chip surface was grounded as long as it is gray)and then plugged the data cable. Release the tweezers when the current reaches up to 700mA～1A shown in the power meter, then as long as the CPU’s working conditions could be satisfied, the Aisi assistant software in the computer would point out the connection of DFU mode, then if restore the phone, the reporting of error 4005 would occur. The capacitor C1501 in the bitmap is shown in Pic 5-50. The capacitor C1501 and the hard disk power supply PP3V0_NAND in the circuit diagram were shown in Pic 5-51.
Pic 5-50 The capacitor C1501 in the bitmap
Pic 5-51 The capacitor C1501 and the PP3V0_NAND in the circuit diagram
Forcing into DFU here was only for judging whether the working condition of the CPU was normal, therefore, to roughly judge whether the lower layer of the CPU was normal or not.
This motherboard could be connected after being forced into the DFU, in accordance with experience, it should be caused by the bump when blowing the hard disk which resulted in the damage or pseudo soldering of the upper layer of the CPU. After the motherboard was warmed up for 1 hour, the upper layer of the CPU was separately removed (the temperature should be handled properly). After the removing of the upper layer and the completeness of the cooling, the current may be up to 80mA fixed which could deduce the problem of the upper layer of the CPU. After replacing the upper layer of a CPU, the phone could be switched on normally. This phone was solved.
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