Z5 show "no service" with workable sim card

[HEIMAN1]

I have currently bought a new xperia z5 and it have no mobile network service most of the time.

It did have network service for about 1 day once but since then the device cannot find the network anymore.  Rebooting the phone or turning flight mode on and off will sometimes result in a successful network connection for half a second and immediately back to the no service situation.

I have tried swaping a sim card which is workable in a xperia C3 and I have also tried the Xperia Companion Software Repair but nothing change.

Upon searching through the internet I saw plenty of the xperia users having this issue since the 7.1.1 update but none of them can find a solution.  I believe this must be something to do with the latest system update patch.

Please help to adjust the issue.  Thanks.

[Aljeraisy]

Dear friend,

I used to have weak signals when I bought the mobile 2 months ago. The problem to me was a weak LTE signal provided to me, I went on Settings > More > Mobile Networks > Preferred network type ... I kept changing between them till I found the one working perfectly. I hope it works with you

Note: The signal was differential from time to time and place to place.

[HEIMAN1]

Thanks for your reply.

I have tried switching the preferred network type multiple times.  For one single time, the mobile signal had pop-up for 1 second when I changed to "WCDMA only" and it went off again immediately.  Other than that the nothing seems to be changing when I switched the preferred network type.

I have also tried the method suggested in message 13 of the post "Xperia Z5 keeps losing mobile network connection".  Switching network type in *#*#4636#*#* also not seems to be working.

Anyhow, thanks again for your suggestion.

[Aljeraisy]

So I suggest you to vist your local care team in your country..

You welcome anytime.

[HEIMAN1]

Recently I have observed an interesting phenomenon.  When I switched on the phone for the first time after factory resetting, it showed normal network connection.  But immediately, the message "your device will now restart to be optimized for your network operator" showed up and forced me to restart the phone.

 

After the "optimization", the network dead again.

This really seems to me a "network setting" problem instead of a hardware failure.  Any idea what did this optimization change?  Is there any way to switch back these changes manually?

I hope this discovery helps in providing more information about the network connection problem.  Thanks

[Aljeraisy]

Then go to Settings > More > mobile networks > services providers

search on your providers and register on it manually... This may help you.. For your know searching and registering take few minutes in loading so don't cancel it.

 make sure you are registering on your sim providers network. Then turn on and off airplane mode.