Vizio GV42LHDTV - No video inputs

Question

Hi
This sets RF (Cable) input works great. I get SD and HD and the pix are great. Problem is none of the Component A/V, Composite A/V or HDMI inputs work. On composite adn component, the input display screen comes up but there is no pix or sound. (HDMI video is intermittnet and audio gone.) Been trying to find service manual before I take it apart but having no luck. Is there a separate video input board that may be culprit?

Apperciate any advice anyone can give.....also saw referene to service codes, what are these?

Thanks in advance