OK are you sure the aerial is good enough and did you check the connection at rear of box i.e the coax plug, no bits of outer braid touching the inner core. Then you should check and make sure the tuneR is fiTted snugly on the board, means opening the box and look carefully at seating and then press firmly but not too firm.
Then I would try another image i.e vix and use 6.4 dont use 6.5. Go menu, setup, software management, flash online, press yellow distribution, then openvix and follow onscreen prompts, box will make a backup and when flashing will ask if you want to restore but if you are handy do a clean install, its straightforward BUT make sure you select an empty slot and not the current one as it will overwrite 7.3 so be careful.
If SAORVIEW still poor after all that then you can assume dtt TUNER is duff. I would then get a sony playtv usb tuner, I have 4 of them, and disable the onboard tuner, set up the USB one and voila you now have a TWIN TUNER for SAORVIEW. A lot cheaper than buying another box.