There are many reasons to caused your iPhone 6 cannot be turn on, two case have been mentioned before. Now, let’s introduce the third situation. The iPhone 6 won’t turn on after water damaged. The problem is the iPhone dropped into the water, then it leaks 60mA current, and then cannot turn on.
First, disassemble the screen and battery and plug adjustable power supply to energize it. The current is 60mA. When press the power button, the current stops at about 120mA. Remove all the shield cover and find that some of capacitors of the main power supply PP_VCC_MAIN turn black.
According the circuit principle, we need to judge whether the electricity leakage is from the circuits of battery power supply PP_BATT_VCC or main power supply PP_VCC_MAIN.
Above all, we remove the field-effect transistor Q1403 that converts battery power supply into main power supply. The Q1403 in schematics circuit diagram is shown in picture 1.Then,plug adjustable power supply. If it still leaks, the circuits of battery power supply PP_BATT_VCC leaks. If it does not leak, the circuits of main power supply PP_VCC_MAIN leaks.
Energize it and test. The voltage-stabilized power shows no electricity leakage. Based on repair experience, for water-damaged iPhones, we first consider display power supply IC, backlight IC and main power supply as well as capacitor (The electricity leakage from the filter capacitor at the circuits of main power supply PP_VCC_MAIN cannot lead to turn on failure).
Assemble Q1403 and put a thin layer of rosin on the surrounding parts of display power chip U1501 and backlight chip U1502. Then energize to find the hot components. The display power supply chip and backlight chip with rosin is shown in picture 2.
After few minutes, we notice that the rosin is not burning. If the electricity leakage is from capacitor, function chip or baseband chip, we could fix first and then turn on to test its function. Use the problems from functional circuits to ascertain a general faulty area.
The motherboard has 120mA current that minus the leaked 60mA. That means when at the moment iPhone turned on, its current is 50~60mA which is caused by the damaged circuits at the working condition of CPU, I2C0 bus, I2C1 bus and large power supply chip U120.
Energize iPhone and measure all the power supply of CPU. All the power supply voltages are normal except the voltage PP_GPU (This voltage can be measured only when iPhone is turned on normally). Then we measure the I2C bus and find that the voltage of AP_TO_I2C0_SCL is 0.3V. This kind of trouble phenomenon can be found only by measuring the diode data to ground. If the diode data to ground of I2C bus is high while the voltage of I2C bus is low, the pull-up resistor and CPU have some problems. If the diode data to ground is pulled down or short circuit, we have to tear down the chips one by one to judge. We can measure the I2C0 bus circuit at resistors R0302 and R0303. The pull-up resistors R0302 and R0303 at I2C0 bus in bitmap are shown in picture 3.
Deenergize iPhone and measure the diode data to ground of AP_TO_I2C0_SCL. The data is 33. I2C0 bus flows to CPU, display power supply IC, backlight power supply IC, USB chip and large power supply.
After water getting in, that the diode data to ground of I2C0 bus is pulled down is often caused by displays IC and USB chip. First remove display power supply U1501 and energize iPhone to test. The electricity leakage disappears. Short connect it and turn on. The adjustable power supply shows 1A current. The current jump turns normal and iPhone can be turned on normally. Remove a display power supply chip U1501 from accessories board and assemble it on this faulty motherboard. Triggering it on, the white Apple loge appears and it enters boot screen. The iPhone 6 can be turn on normally.
The display power supply chip U1501 in schematics diagram are shown in picture 4.
- If the hot parts cannot be found, we can leave it and skip to fix the problem of turn on failure. In most cases, if the problem of turn on failure disappears, other problems will disappear too.
- If the problem of turn on failure disappears, but some function is still unworkable, we can find the faulty points by entering IOS and testing.