Firstly, try to fix it by replacing the iPhone 8 speaker and Mic accessories.
Use screwdrivers to disassemble the iPhone 8, remove the iPhone 8 speaker and Mic accessories, and then install the new speaker and Mic accessories. Assemble the iPhone 8, and test it, unfortunately, the iPhone 8 speaker and Mic still don't work when calling.
Remove the iPhone 8 from your phone's open tool, remove the iPhone 8 speaker and microphone accessories, and install a new speaker and microphone accessory. Assemble the iPhone 8 and test it, and unfortunately, the iPhone 8 speakers and microphone still don't work while you're on the phone calls.
Go to check iPhone 8 recording function, the speaker is working, it can be recorded, which means the iPhone audio circuit is normal. Log in to ZXW online account to check iPhone 8 schematic diagram, we suspect there is a problem with the exchange of data between the iPhone 8 main CPU and iPhone communication CPU.
Use phone opening tools to disassemble the iPhone 8 again, remove the iPhone display assembly, disconnect the iPhone 8 battery, and take off the iPhone 8 motherboard.
Use digital multimeter to measure the RF board, the S57 Pin resistance value measured is 0.006, while the normal value should be 580, is this caused by a burst of tin in the iPhone 8 communication CPU?
Attach the iPhone 8 motherboard to the PCB holder fixture, use hot air gun to remove the iPhone communication CPU, and then measure it again, but the resistance value for S57 Pin is still abnormal.
Check the middle frame of the RF board, use tweezers to remove the middle frame, and then measure the S57 Pin again, now the resistance value is normal.
Re-install the iPhone 8 middle frame and communication CPU, and then use ISocket test fixture to test it, the speaker and Mic functions are working properly.
Finally, install the iPhone 8, and test the iPhone 8 functions, all works well.