LM2596 DC-DC converter

Hello All,
I recently purchased 10 of the LM2596 converter PCBs and, being clever, I’ve ditched all of the paperwork so cant remember from where I bought them. Duuuuh me.
I tried to use one today and found that I could not get the output to vary so I assumed that it may possibly be defective. I have now tried all of the others and have got the same problem with all of them.
I have checked the spec for the trim pot,Bochen3296, and it is a multi turn W103 pot. The inductor is a 47uH, marked 470.
I would be grateful if somebody can tell me what stupid thing I am doing please.
Thanks all.

Give some extra information, at least a picture of them would help. Try to find similar product and provide link as well.