Share your experience!
I am using xperia z ultra (c6802) with. 510 latest firmware i am facing a serious issue my phone screen is switchin off and then it is not oning there is black screen backlight is on but nothing appears i have to reset phone by pressing 3 buttons simultaneously . (i.e volume up., volume down and power button.)
I am facing this very frequently.
Please help me.
I heard this issue was solved in. 510 FW but i am still facing this issue.
Please help.

See if a software repair using SUS helps
Update/Repair your phone via SUS
SUS ( Sony Update Service) ... download and install it on pc and follow the on-screen instructions
http://www.sonymobile.com/global-en/tools/update-service/
We just recived a new firmware. 525.
Update your device first after run a Sony Update Service (it will wipe your garbage and rom will be installed again on "clean" phone)
For now many users around the word still have a SOD issue's even with 525 !!!! 
Stay tuned I hope sony devs working on fix.