I have a Panasonic NV-HD660 which has worked well for several years. But, I think that its developing a fault When I play a tape, the picture keeps going slightly darker and lighter. It cycles between dark and light approx ever 3-4 seconds. The effect looks similar as what you get when trying to copy something with Macrovision on. But the effect is very VERY subtle and some people might not even notice it.. But its driving me nuts and I want to fix it! Any ideas what this could be?