Firstly, we need to fix iPhone black screen problem. Disassemble the iPhone 6 by phone opening tools; we can see that there are repaired traces on the iPhone 6 motherboard.
Remove the iPhone display assembly, disconnect the iPhone battery, and then take off the iPhone motherboard. After observing the iPhone motherboard, we found there are 3 screws are twisted deep.
Use Fluke 17B+ multimeter to measure the iPhone, there is no screen power supply ±5.7V, the iPhone 6 doesn't display and it has no backlight.
One of the four circuits is the open signal LCM_TO_CHESTNUT_PWR_EN of display power supply chip, sign in to the ZXW online account to check iPhone 6 schematic diagram, we know that this signal connects power supply chip U1202.
And the signal LCM_TO_CHESTNUT_PWR_EN also connects to the display power supply chip U1501.
The signal LCM_TO_CHESTNUT_PWR_EN connects to display socket J2019 through the inductor FL2035.
Measure the 16 Pin of the display socket, there no diode data, which means that it's disconnected. Use JBC soldering station to solder a jumper wire, and then measure it again, now the data measured is normal.
Disassemble the iPhone again, use digital mulitmeter to measure the diode data of the iPhone earpiece connector, it's normal.
Use QUICK 861DW rework station to remove the iPhone audio IC, after measurement, we found the C9 Pin is disconnected. Based on iPhone schematic diagram, we know that this Pin is connected to CPU.
After checking, we found the second layer circuit is disconnected, and then it causes this problem. Use JBC soldering station to solder a jumper wire from iPhone audio IC C9 Pin to this point, and then fix it with green UV oil.
After soldering these jump wire, assemble the iPhone 6. Turn it on, and test it, now the receiver sound is normal, all other functions are normal too, the iPhone 6 has been repaired!
I hope the above methods will help you. If you have other better repair methods, please leave us a message in the comments.