I now think the problem is with the one of the HD signals interfering with the SD transmissions on Freeview.
Like you I'd attempted various solutions over a six month period to fix the problem without success and, again, like you decided to purchase a separate Freeview set-top tuner and feed the output to the Bravia TV using it purely as a monitor.
I purchased a Manhattan unit @ £44, the terresterial TV tuner (They also do a Freesat version) has Freeview HD and SD receiving capability, supposedly a record capability to USB (But I haven't attempted to use this facility yet) and it has a limited smart TV internet capability (The internet locations you can visit are pre-programmed into the tuner and are not capable of change by the user - there's no URL bar).
Personally, I didn't want to spend out too much, as I suspected, that Sony, like the other white goods manufacturers, are probably producing the current generation of TVs with sub-five year design lives (Fully expecting the power supply or screen to go)o
- something about price point sales maximisation in the new global economy with the object of maximising the owners of capital returns ?
Anyway, to get back on topic, I set-up the Manhattan unit to feed its output to the HDMI 2 port on the Bravia TV and had no problems getting a signal. However, at first, whilst the Manhattan tuner automatically scanned for HD and SD channels and found all available (Although not as many channels as the Bravia's internal tuner ! Not as sensitive ?) it would not display any of the HD channels.
Now, according to the Freeview web site, I was able to determine from the postcode database and the signal coverage map that I should be able to receive BBC 1 & 2, ITV 1, Channel 4 and Ceebees in HD.
The Manhattan Tuner detected all the HD channels which the Freeview website predicted, but it would not display a picture for any of them on the Bravia TV.
After a bit if research on the web, I learned that the HD channels received from my local transmitter, Crystal Palace, could be made to display a picture if each HD channel entry was manually deleted from the channel database built during its own previous automatic scan ! - the Manhattan unit has a facility for manually deleting channels. All the HD channels to be deleted were in the range channel 100-110.
Outcome: When I deleted these channels manually and restarted the Manhattan tuner, BBC 1 & 2 (On channels 1 & 2, which previously showed only an SD picture and symbol) now showed an HD picture and symbol. Same with Ceebees. However, ITV and Channel 4 still displayed an SD picture and the 100+ HD channel entries for these were lost.
The HD signal seems to display best in 720p, although my Sony TV will do 1080i.
Subsequently, I've tried multiple times re-booting the unit and going through the auto-channel scan and manual deletion process but the tuner/TV combination will not display the commercial TV channels in HD.
So either the advice on the Freeview website is wrong and ITV and Channel 4 are not being transmitted from Crystal Palace (Doubtful) or there's a signal transmission conflict which manifests itself on SD only capable Sony's TVs with this re-booting rubbish. The fact that the Manhattan tuner is unable to display ITV HD and Channel 4 suggests to me that the fault is with the TV signal transmission rather either the Sony TV or the Manhattan unit.
I wonder whether this is a consequence of the BBCs recent ponderings what to do with BBC 3 & 4. Now that's been decided, and BBC 3 is moving to the web, there's bound to be in due course another re-shuffling of channels across the multiplexes and perhaps the interference on Sony's SD capable TV tuners (Which appear to be very sensitive) will disappear and other HD channels will have space to pop-up.
Nick
