Today we are going to talk about the third
case of iPhone 6 cannot turn on after water damaged. This case is iPhone 6
dropped into water, then it leaks 60mA current, and won't turn on.
First, disassemble the Display Touch Screenand 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 1-1.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.
1-1
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 1-2.
1-2
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 1-3.
1-3
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 1-4.
1-4
Tips
1. 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.
2. 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.
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