Here are pictures of the category boards and descriptions of how they changed. I'm ignoring the actual categories in this section.
Series 1: Red, green and black concentric circles on a two-board rotating frame. This is the only series with green in the category board.
Series 2: Black, white, red concentric circles on a two-board rotating frame.
Series 3: Same as series 2.
Series 4: Same as series 2 and 3, but now it is on a 3-board rotating frame.
Series 5: Same as 4, but with a blue neon light around the outside.
Series 6: Yellow arrows all pointing at a black, white, red board, all surrounded by blue neon that doesn't reach all the way around the board. The same board design lasted up to and including series 14, although there were minor variations in the gaps in the blue neon.
Series 7: Same as series 6.
Series 8: (Possibly irrelevant: a slightly larger gap in the top of the neon.)
Series 9: (Possibly irrelevant: A larger gap in the top of the neon, while the bottom of the neon reaches further around. Presumably, it's the same length of neon but it has slipped down a bit.)
Series 10: (Possibly irrelevant: No gap in the top of the neon.)
Series 11: Same as 10.
Series 12: Same as 10 and 11.
Series 13: (Possibly irrelevant: very tiny gap in the top of the neon.)
Series 14: Identical to series 13, as always.
Summary: Series 1: black, green and red rings. Series 2 and 3: black, white, red rings. Series 4: same as 2 and 3 but on 3-board rotating frame. Series 5: same as series 4 but with blue neon lights around outside. Series 6 to 14: yellow arrows on a black background.
The categories in the category round for each series were as so:
1: food, places, sport, showbiz, Bible, history, books, myths, art, spellingIt is usually easier to use other characteristics to identify series than the category board categories.