The reasons that causes iPhone 6 Plus call failed and no service includes software reason and hardware reason.
Common software reasons are network problems, Apps problems and iPhone iOS problems.
Common hardware reasons are iPhone RF power chip and U5411_RF.
Some phone repair tools are required before repairing:
-- iPhone SIM Card Eject Pin
-- iPhone lightning cable
-- iPhone opening tools
-- WUXINJI Dongle
-- Hot air rework station
How to solve?
1. Make sure your account in the normal use
Some carriers would impose a temporary disconnection to accounts that are tagged as delinquent. Contact your carrier or service provider to verify and check your account status if you suspect that this problem has something to do with it.
Also check with your carrier for outages and network problems that may have affected calling services in your location.
2. Restart iPhone
Restart iPhone can solve many software problems that caused by Apps or other software error. In order to restart iPhone:
Press and hold the Top (or Side) button until the slider appears.
Drag the slider to turn your device completely off.
After the device turns off, press and hold the Top (or Side) button again until you see the Apple logo
3. Reinstall SIM card
Sometimes the iPhone no service is caused by connection between iPhone SIM card and iPhone, we can solve it by reinstalling.
Make sure the iPhone is completely turned off, use iPhone SIM Card Eject Pin to pop the SIM card tray out, and then gently remove and then re-insert the SIM card.
4. Restore iPhone
Restoring the iPhone can solve the software problem most deeply，because it will erase all data on iPhone, including all information and settings. So, you need to backup your iPhone before restoring.
Use iPhone Charger Cable to connect iPhone and computer, and then use iTunes to restore iPhone.
5. Disassemble iPhone
Use phone opening tools to disassemble the iPhone, and then carefully remove the iPhone logic board.
6. Measure the iPhone logic board
Check iPhone schematic diagram on WUXINJI Dongle, we know that the RF power chip and U5411_RF will cause this error.
According to our experience, the iPhone signal turns weakness when it in charging is mostly caused by the damage of U5411_RF or the working condition is not qualified.
Use digital multimeter to measure the iPhone diode data between the two power supply pins of U5411_RF and two signal wires of the RFFE bus, the data is normal.
Use Lead Probe Needle Tip to touch the L5408_RF inductance when measuring the voltage, the inductance becomes askew and becomes black at the ends of it.
7. Repair iPhone logic board
Put iPhone under the Trinocular Stereo Microscope, and then use tweezers to remove the L5408_RF inductance directly, and then use QUICK 861DW to solder it with tin.
Assemble the iPhone and test it, now the signal and phone call function all works properly.
These are some of the ways to fix the call failing issue on the iPhone successfully. I hope these solutions can help you out of this problem. If you have other questions, please leave a message in the comments.