First of all, we need to disassemble the iPhone 8. Use Screwdrivers to remove the screws at the bottom of the iPhone screen, and then use LCD sucker to open the iPhone screen. Remove the iPhone screen, disconnect the iPhone battery, and then take out the iPhone 8 motherboard.
Put the iPhone motherboard under a Trinocular Zoom Microscope to observe, obviously, this iPhone 8 was been repaired before, because there are repair marks on the iPhone baseband part and iPhone baseband power part.
Observe it carefully, we found that there are several tin balls on the iPhone motherboard antenna plate, which is abnormal. We suspected this is the reason that caused the iPhone 8 shows no service.
Use hot air gun and Titanium Alloy Tweezers to remove the iPhone antenna plate, clean the solder pad, and then reinstall the iPhone antenna plate to the motherboard.
Now assemble the iPhone 8, press the power button, the iPhone is turned on smoothly. After get into the IOS system, we can see that the signal is back, the iPhone 8 can make the phone call successfully.
Hope this guide can help you fix iPhone 8 "No Service" issue. If you have any new idea, please share it in the comment section.