My sone plays his playstation 3 on an old Sanyo TV but has lost the remote and cannot acces the av channel - help please

Check for an input button the TV itself. Otherwise try a universal remote and attempt several codes.

You can also check the menu, some TVs (not many) have the ability to change inputs in the menu. Usually you can use the channel and volume buttons on the TV to change inputs.

If you have a cable box remote or similar programmed to control the TV's volume and power, it might be possible to change inputs using that. Usually all you have to do is press "TV" then keep tapping an "input" or "source" button.