It sounds like you might have an intermittent short inside the picture tube. It might be fixed by connecting the tube to a restorer/analyzer (a.k.a. rejuvenator). Take it to a tv repair shop and they charge around $50 to $75 to 'zap' it.
Do a search for your make and model on the newsgroup sci.electronics.repair to see what other problems/fixes others have experienced. My own opinion of Sanyo products is that they are bottom-of-the-barrel CRAP. Repair parts are overpriced, not usually in stock, and the parts dept won't even talk to you unless you buy a service manual from them first! I have a Sanyo microwave oven and I had to wait six months for parts to arrive from Japan! Sanyo sucks.