So you have already done a full Factory Reset, could have told us that from the start,
would have saved us from suggesting things you have already done.
Are there any other things you have done to address the issue.
Tell us about the TV, did you buy it new, when did you buy it and where from.
Do you know if it is still under warranty. Some retailers offer multi year warranties.
Did you register it with Sony, did Sony offer you a 5 year warranty.
Did you notice this problem when you first bought the TV or is this something that has happened recently.
If you think you have tried all you can to rectify the issue then you may need to request a repair as it is looking like one of the tuners has failed.
Have you tried the TVs own Self Diagnostics.
Click the Settings button on your remote control.
From the pop up menu scroll left and click on Settings.
Scroll to the bottom and click on Help & Feedback.
Now click on Help.
Click on Status & Diagnostics.
Click on Signal Diagnostics.
If you are only watching one channel and not recording another the diagnostics will check the signal
by default on Tuner A. (you have to scroll right down to the bottom of the list to see which tuner is activated.)
If you find that the TV is using Tuner B, then we can suppose Tuner A is not functioning.
This next procedure probably will not work for you as you cannot switch channels whilst recording
but this is what I would do to test both tuners.
Set up a recording within the TV guide. For example Channel 4 HD. Choose something that is due to start soon.
Now select another channel to view, this must be a channel broadcast on a different multiplex (mux).
For example something on the Dave channel.
Whilst viewing the programme on Dave go to the Signal Diagnostics it should show that signal is on
Tuner A.
Exit the diagnostics and with the recording in progress switch the TV over to Channel 4HD
Go back to Signal Diagnostics scroll to the bottom and should confirm that Tuner B is being used.
As I say though this will not work for you as you are unable to switch channels whilst recording.
Also try the Self Diagnostics to see if it gives your TV a clean bill of health, not sure if this test the tuners though.
Perhaps royabrown2. has more information on how you could perhaps check if both tuners are working or not.
