I believe that it could be the SIM card holder now that you mentioned, a couple of days ago I swap my logic board to a new housing with new antenas and the issue remained unfortunately in my country there is no authorize repair center
Jordimdza wrote:
....unfortunately in my country there is no authorize repair center
That's bad, Jordimdza. Sorry about that.
I hope you can work it out.
Best of luck.
Giulio
What iOS version are you running? (Settings>General>About>Version)
If the "old" computer was able to update your device, you should have 11.4.1. If so, the "old "computer has no fault.
Now, as far as connection issue is concerned, you can try and reset network settings:
Settings>General>Reset>Reset Network Settings
When done, restart your iphone
If the issue still persists, it could be a hardware failure (antenna? SIM card holder?).
Have your device inspected at your most convenient Apple Store or Authorized Service Provider:
Apple - Find Locations - Location Selector
Regards
Giulio
IPhone 6s drops network service after update