old zenith ringing

[maxhifi]

Now that my old Zenith portable is displaying colours accurately, another issue has made itself visible.

I am not sure if ringing is the correct term, but will attempt to describe. When text is on a strongly contrasting background, a shadow of it can sometimes be seen to the right, but never the left.

This is a different phenomena than when brightness is excessive, and the entire text goes out of focus. It is most especially noticible with black text on a white background. during video which doesn't involve titles or graphics, it is not noticible at all, and if the background is lower contrast, say green on grey, not noticible either. Any ideas what causes this effect?