When I turn on the tv, I get no picture, but I do get sound. However, the sound starts couting out after like 3 minutes and they completely goes out after about 4 minutes. If I unplug the tv for 15-20 minutes and replug, I get sound again...for another couple minutes until it come outs. What could my problem be? Does anyone have a schematic for my model or any model close in number? Thanks.