The customer sent us an iPhone 6s needs to
be repaired, the fault described is that it reports unknown error 4014 when flash
it. After detecting, the current is 57mA, DFU mode, flashing it and it reports
4014, which is consistent with customer description.
Disassemble it to check the iPhone
motherboard, the iPhone Nand flash on this motherboard has been repaired, and
when check it under the microscope, we can see that the iPhone NAND flash
damaged.
Remove the iPhone Nand flash and measure
its diode data, it is normal. Put Nand flash into the WL PCIE Nand test programmer to test it, unsurprisingly,
the NAND flash is damaged.
Replace the new iPhone Nand flash and flash
it again, the fault still exists. As we know, the iPhone 6S and later iPhone
reports iTunes error 4014 mostly caused by nand flash and baseband issues.
However, after measuring, we know that the iPhone Nand flash is good, so now
the problem is iPhone baseband. Measure the diode data of baseband power
LDO part and S1-S5 power supply, all is normal.
Flash it again, test the S2 and S4 when the
White Apple logo appears, there is no power in either of these places. Since S2
and S4 have no power, it is possible that the baseband power supply does not
work and then can't output power. Remove the baseband power, and then use Fluke
15B+ Digital Multimeter to measure it, we found the 55 pin is to
ground.
55 Pin connected to the 19.2M clock, put
iPhone motherboard under the VGA Camera 7-45X Trinocular Stereo Microscope to observe the 19.2M clock.
19.2M clock with C3501_RF capacitor
grounding end connected together
Handle the baseband clock well, and then
flash it again, now the progress bar can run normally, and iTunes doesn't
report unknown error 4014 anymore.
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