Well, assuming that the screen should be blank then piggybacking UC6 has actually incorrectly added $0F to the correct $20, whereas what we want is to subtract $0F from the slash $2F turning it into $20, no? Or have I got something wrong?
Piggybacking a good RAM on top of a good RAM should do nothing. Piggybacking on a bad RAM might do something (any change is good indication).
@Brian: When the screen alternates / and space, can you tell whether the space is at the beginning or end of the line?
This would be good to know. But it may be hard to tell now that I think about it, as there are blank spaces before and after the actual lines. I'm not sure why I thought it was the odd addresses that were bad. Piggybacking UC4 may give us more info.