I worked on Sony TV for 20 years. Your problem sounds like a cold soldier joint to where the tuner mounts to the main board. Sony as well as other brands use wave soldiering to the board. The tuner connections are usually pretty heavy solid conductors to support the tuner housing. If your savy with a soldiering iron heat and apply soldier to each connection between the main board and tuner. Make sure you get the tuner leads hot and that soldier flows well. DO NOT move until the soldier has ample time to cool throughout. Give it a minute you might create another cold soldier joint if you get in a hurry. Be careful heating the printed circuit board connections they are then as paper and you might lift it from the board if your not careful. I recommend then taking a old tooth brush and some alcohol and cleaning these connections. They should be shinny if they look rough after you clean them redo that connection it is a cold joint. In 90% of Sony TV's this was all that was wrong with them when they had tuner issues. Power supply is second to fail and not for the casual user to attempt to fix. Be careful inside the set there is some nasty high voltage that can stay with the picture tube for days with it unplugged! Don't forget to say clear of any electrolitic caps as well. They will hold a charge for day on end as well. Good luck Richard Hopkins