Thanks STeevsee and all others for the input so far...
...did I even do the correct test 
Sounds like the right test even though it's on a different page in my copy of the guide.
Columns 7 and 8 (pins 7 and 9) are not used in CFTBL(not sure why 6 not working?) but column 4 should certainly have registered if U20 was ok.
Hate to say it Wotto, but it looks like it's time to replace U20.
