Hi ftlocks!
The thing to remember with the cryptics - and it is so easy to forget, I do it all the time - is that a word can have many meanings when used in a different context. For example, if the clue talks about 'going out to play' you can spend so much time thinking about school friends, games, toys, etc. and then suddenly the penny drops that the answer is 'theatre' or 'drama' or something like that.
With that in mind, have another think about the clue in question -
Inspector sometimes goes on board.
You might immediately think of a transit inspector getting on board the bus or train checking that passengers' tickets are in order. Yes, in that context he/she is a 'checker', but have you ever actually heard that term used? I haven't - they have always been 'inspectors' to me.
However, bearing in mind that inspectors are checkers.......
Who or what sometimes goes on
a board?
what kind of board? Board of Directors? Ouija board? Chess board? Checker board?
Fanfare please!
So, a checker sometimes goes on a board. So in this case 'board' was the word you had to find another context for.
I hope that didn't sound too long-winded - once you get your mind into the trick of changing context in mid stream it all makes sense!
(Maybe!)
The resident expert on cryptics is definitely Butterfly - I feel she is on holidays at the moment - but I'm sure she could explain it much more clearly than I have.
Good luck!