Random restarts

[Bendy]

After an os upgrade requested by my phone  last week it now does random restarts, when being used or when just on the charger or it just can't find a network for a while. It gives no indication or warning as if Cnt+Alt+Del were used. No notification messages before or after restart. Android CrashMonitor doesn't seem to work. No apps were added or upgraded.
This doesn't look like a faulty SIM. It seems to be a faulty os or a an os/app clash. Rather than remove an app at a time and wait, is there any system monitor log to view?

The upgrade was performed with a usb cable only i.e. without PCC or other software.

Android 4.1.2

Baseband version 8660-AAABQOLYM-314010-39

Build number: 6.2.B.1.96

[Sane4ka]

+1

[Uliwooly]

Repair your phone with SUS 

Update Service (SUS)

http://www.sonymobile.com/gb/tools/update-service/

http://www-support-downloads.sonymobile.com/Software%20Downloads/Update_Service_Setup-2.11.12.5.exe

PC Companion (PCC)

Bridge (for Mac)

Alternatives on How to backup Xperias

http://talk.sonymobile.com/thread/36355

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[Bendy]

Thanks, I completely reset my phone with the latest software and loaded only four very common apps. I've been testing the phone since then.

The faults are:

 - random restarts (same as before the rebuild)

 - randomly shows no signal, untill i manually go into settings->More...->Mobile Network->Network Operators

 - randomly switches from speaker+vibrate to vibrate (only) and it doesn't switch back. I have missed messages and calls becaus of this!

By random I mean random, no operational pattern preceeding.

These faults seem to not be affected by the following being on or off; bluetooth, wireless, mobile data, Extended standby Mode.

These performance errors are now critical. Find a solution Sony.