Sorry for the duplicate post. Computer had frozen and I didn't know how to delete the second post!

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Hello,

I am trying to diagnose a problem with a 14" Grundig CUC7303 television. When using the built-in antenna, there are diagonal lines across the screen for each channel. On certain channels it is not as bad.

The strange thing is that, when an external antenna (Outdoors) is connected, these diagonal lines appear to go away?

I assumed that this may be a problem with either the tuning or I.F circuitry?