Whilst watching tv after 10 to 15 min screen goes blank but sound ok ,when u turn tv off then back on u get pitcure for about 10 minthen goes off again

I had this problem on my 42" Philips. Just got it yesterday and worked fine on the tv stand. As soon as I mounted the TV to the wall via wall mount system, I had the exact same issue you did. Figured it out today.

The wall mount was putting pressure against the center of the back of the tv (tv set had a slightly rounded back plate, and the mount was a flat plate). As soon as I put spacers (part of the wall mount hardware set) between the wall mount braket and the tv so there was no contact except at the mounting holes, the tv worked fine.

My theory is the pressure pushed the tv back plate against some board components which caused them to overheat (no air flow); or put pressure on internal connectors. I dont know.

Hope this helps, may not apply to your situation.