I have a mystifying problem with the Freesat tuner on my 10 month old KDL-40Z5800.

For the first 3 months or so Freesat was fine, I was able to receive all the channels including the HD channels.  But then soon after the TV prompted an upgrade in May I started losing channels intermittently. Initially it was True Movies & some others, but some days I would lose BBC channels, then the next day they would be OK again.  I tried retuning – some times I would get the channels back & other times not, but it gradually got worse to the extent that when I tried to retune the TV it would tell me that no satellite signal was being received.

I am currently unable to tune any channels via Freesat, but – if I retune using the DVB-S option rather than Freesat, it finds about 900 channels. 

The satellite feed comes from a dish/quad LNB with 2 of the other cables connected to a Panasonic DMR-BS850EB (HDD Blu-Ray recorder with twin Freesat tuners) in another room. I have had no problems with the Panasonic box, and have tried it with the satellite feed that is normally connected to the Sony TV & it is fine.

I have had a satellite engineer out to check the signal, and he confirmed that all cables from the dish were providing a strong signal. I have now had the TV checked by my local Sony service centre. Having checked that all software/firmware was up to date & OK & confirmed the Freesat tuner was working OK, they delivered the TV back, only to find I still had the same problem!

So apparently the signal is fine & the TV is fine, but I cannot tune any channels via Freesat.  What could the problem be?