I thought I would add the latest update - had the cable company here yesterday and installed a brand new cable. Of course, wouldn't you know it, yesterday
the cable was not causing lines on the tv.
Anyway, we plugged the new cable directly into the back of Magnavox, and all looked as perfect as you get with standard definition! I thought all my problems were solved.
Then, this morning, I switched on the tv and about 30 minutes later, the lines were back.
The cable was plenty secure in the Magnavox - in fact I could barely unscrew the bloody thing to check it on the Panasonic! My fingers are still sore from that! Anyway - no lines at all on the Panasonic. I plugged the cable back into the Magnavox and it cleared up for a short time, and then the lines came back with a vengeance. I had the tv on all day because I wanted to see if I was losing my mind regarding the lines randomly appearing and disappearing, only to reappear. The length of time that the lines were there was far greater than the length of time they went away.
So on the up-side, I am not losing my mind. On the down-side, the lines do
randomly appear/disappear/reappear, without any movement of the cable whatsoever.
With it being all new cable (I mean, the guy ran a new cable outside, secured it, ran it inside, tested it, blah blah blah - I don't know what else we could've done) and the problem still occurring, I have decided to return the machine and order another. The cable guy said that this particular Magnavox model works really well with their cable - he likes it for himself. So I am back to thinking there may be something awry within the machine itself.
I will update again once I have a replacement and report whether or not the problem is resolved.