Recently, Vipprog made
a guide on the repair iPhone 6s Plus displays Apple logo after power on and
then continuous reboot. This iPhone 6s Plus was broken once and repaired, but
not working.
Firstly, root by iTunes, and it shown 4013
error code. It will display UDID information when using i4 software to root. Generally,
the showing of Apple logo and reboot and reporting error code 4013 most because
of the damage of NAND Flash IC. But this
iPhone can show UDID information, so NAND FLASH IC is not likely to be damaged.
Second, disassemble the iPhone and found
that motherboard has been fixed many
times. CPU, EEPROM and USB chip are all be welded. First clean the remaining
soldering paste and observe whether these welded places has any component
dropping off under microscope. After
making sure no component dropping off, replace the NAND Flash and root. But
iPhone still reports error code 4013. The problem in CPU is less likely happen.
Third, according to repair experience,
there is a same problem happens because of the short circuit of iPhone 6S power IC. Remove the baseband chip and iPhone
displays white Apple logo and reboot later. Replace a new baseband power chip and everything becomes
normal. After researching the iPhone working principles, we find iPhone 6S
baseband chip communicate with CPU by PCIE bus. During the power on process,
the PCIE bus will be initialized. Therefore, the improper work of baseband will
lead to white Apple loge showing when power on.
Fourth, Find a normal iPhone 6S and reboot
it. Measure the baseband power supply when it shows white Apple logo. The power
supply exists already and the working condition for baseband has been
satisfied. The baseband supply’s bitmap is shown in picture 1-1.
1-1
Fiveth, Root the faulty motherboard and
measure the baseband power supply when the white Apple logo is showing. We find
that PP_0V9_SMPS1 and PP_1V0_SMPS3’s power supply has been produced, while
PP_1V225_SMPS2 and PP_1V85_SMPS4 has not. That suggests there is nothing wrong
with baseband power. It is very likely that the baseband chip is empty soldered or damaged. The circuit diagram of
baseband power supply is shown in picture 1-2.
1-2
Finally, Remove the baseband and measure
the diode data of the circuit towards chip and CPU. The data is normal. Tin the
baseband chip and weld it on motherboard. Root it and everything becomes
normal. This iPhone 6s Plus has been repaired.
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