I have a stock Series 2 TiVo standalone unit. The unit is about 2 years old. Lately the color has been going out and leaving vertical bands of color (like a rainbow). It will be like this for several hours to several days then go back to normal. All the TiVo menus and screens are in proper colors. I have added a cable booster before the TiVo with no effect. The hookup is basic cable to TiVo, composite cables to TV. I'm thinking one of my tuners is bad but I don't know if I can switch from one tuner to the other to find out. Any suggestions? Or should I just get a new unit?