Most of the electronic products are afraid
to fall, no matter how expensive it is. Okay, maybe Nokia won't. However, today
we're going to talk about a case of a problem after the iPhone was dropped.
This iPhone 6 was dropped to the ground, and the screen is broken. When turn it
on, it shows black screen. When we connect it to DCpower supply, it shows large current. According this, we can know that it
is short circuit. Now, we need to fix it.
First, disassemble the iPhone and energize
the motherboard. The DC power supply
displays 1.7V current that is short circuit and the adjustable power supply
voltage is pulled down to 3.4V. The whole motherboard gets hot, especially the
main power drive chip.
Second, deenergize it and measure the power
supply of each circuit at motherboard through multimeter,
find that the power supply of PP3V0_NAND of EEPROM is short circuit to ground
and the resistance data is 0. The test points of PP3V0_NAND are shown in
picture 1-1.
1-1
Third, use solder iron to make rosin in the
capacitance which connect PP3V0-NAND, then slowly turn the current button of
adjustable DC power supply to increase
the current limit, the inductor that is connected with PP3V0_NAND melts when
the current is 3A. Therefore, this inductor is short circuit. Deenergize it and
remove this inductor, as shown in picture 1-2.
1-2
Fourth, after removing this inductor and
plugging adjustable power supply, it is not short circuit. IPhone can get into
IOS normally. Remove a inductor from the same place of the accessories pad to
replace the old one. This problem was been solved.
Tips:
As this 3V voltage is parallelly connected
many capacitors. It will take long to tear them one by one. Thus we use burn-in
method to find the short circuit point. Put rosin on motherboard and set the
adjustable power supply to 3V. Adjust the current limit to the lowest. Connect
the negative pole of adjustable power supply to ground and connect the positive
pole to the short circuit point. Then energize it. Slowly turn the current
button of adjustable DC power supply to
increase the current limit. The place that rosin melts fastest is faulty.
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