I have sound but no vision on the digital channels on my LG tv bought about 2006

Solution
If these are channels over cable TV then your provider may have removed them. Check with them.
Do you get a picture on any other sources?
If not then it's probably time for a new TV. Cost of repair and lack of replacement boards for a 12 year old set makes it uneconomical to fix.
If you do then get an external over the air tuner and connect it to one of the HDMI inputs on the TV. That will be cheaper than trying to repair the internal tuner.
If these are channels over cable TV then your provider may have removed them. Check with them.
Do you get a picture on any other sources?
If not then it's probably time for a new TV. Cost of repair and lack of replacement boards for a 12 year old set makes it uneconomical to fix.
If you do then get an external over the air tuner and connect it to one of the HDMI inputs on the TV. That will be cheaper than trying to repair the internal tuner.
 
Solution