Samsung Tab3 GT-P5200 10 inch tablet (Thai) o/s fault?

[WorriedNoodle]

Wife's got a Samsung Tab3 GT-P5200 10 inch tablet (Thai) that will not turn off the screen when charging or when the power on/off switch is pressed down briefly is normal on Samsung devices. The only way the screen blanks is when she closes a cover over it. There also appears no way to turn it off, as a long press on the power on/off switch offers no menu option to shut down/reboot etc, but the device simply reboots and only if pressing on the power on/off button for at least 10 seconds. Therefore she cannot turn the thing off completely other than letting the battery drain, and the screen won't turn off unless covered. Other than that device works OK!

In settings we checked if latest o/s installed and it said yes. We also did a (hard?) reset using the power on/home key/up volume combination to get the Android system to reset/re-install everything. All to no effect. I think I read somewhere (cannot recall where) that infact Samsung have a problematic o/s for this device and only option is a root / install go it alone approach which we have no time for (yet!).

Save for wasting a millennium going to a Samsung repair service, anyone got any tips or know if this is a known Samsung problem? Tempted just to junk it and buy another as life is too short, but if Samsung is screwing this up on the Tab3 it won't be another Samsung.