PROBLEM SOLVED
Thanks to all for your suggestions.
Spent a few hours in the workshop (shed) today. Tried the earlier suggestions regarding the address and the slide switch etc.
None of the above made any difference.
I decided to swap the decoder and put it into another loco and the decoder worked normally with sound functions and standing sounds.
Having proved that the decoder was not the problem, I returned it to the faulty F7-A unit.
Powered up the loco and now I have the original problem and started looking at the internal connections between the decoder and the rear sockets. I decided to remove the rear socket from the loco to check the power switch etc. but as I tried to remove the 3 way plug from the F1 socket, the wires pulled out of the plug. This stopped me in my tracks until I realised that I had another F7-A with a replacement sound equipped decoder. This loco doesn't have a 'B' unit therefore the rear socket was not used.
Replaced the rear socket and then all the sound functions F1 to F8 were available.
F6 started the engine into idling mode, (the standing sound), problem solved.
It may have been a coincidence or a bad connection that had started working and to prove it, I may re-instate the original connector board to prove it.
I did try unplugging the F1 connector and the F keys still worked so this connection seems not to be the original fault.
I started this thread stating ''No Standing Sounds' but in hindsight it should have been 'Sound Functions Not Working'
Live and learn and thanks again for everybody's help.
Alan