The iPhone 7 occasionally no signal, so we use iTunes to flash it, but the iPhone stuck on iTunes mode and then reports unknown error 4013. We suspected it's the iPhone baseband reason. Here is the troubleshooting guide.
Disassemble the iPhone, remove the iPhone motherboard.
Use Fluke digital multimer to check whether the resistance of each circuit of baseband power supply is normal. The test points of each circuit can be found more accurately based on the WUXINJI schematic diagram, and the corresponding components can be found on the bitmap for testing.
After
testing, the resistance of baseband power PP_VSW_S4 is only 45, but the normal
resistance value should be more than 500.
This
circuit is connected to main power supply, base band power supply, small radio
frequency and large radio frequency. The cell phone can be properly connected
without taking into account the main power supply. First, the baseband power is
taken down, the resistance is not correct, but i's normal after taking off the
large RF resistance.
Now, use QUICK 861DW hot air gun and tweezers to remove the baseband power and large RF IC, then install the new IC to it. Use iTunes to flash it again, the flash process goes smoothly.
Assemble the iPhone 7, and then get into IOS to test, all functions tested are normal.
Tips:
1. Qualcomm is different from Intel chips, we need to prepare these two kinds of chips.
2. For 4013 error on iPhone 7 or iPhone 7 Plus, basically it's caused by iPhone baseband issue, and for iPhone baseband issue, we can't use iTunes to flash the iPhone, or it will report 4013 error.
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