I think that the safest way to approach this is to use the service menu, go to 'Monitor' and choose 'Reset to Factory Settings'. Make sure that you note all your other settings first thought - go through the normal user menus and take photos, especially 'Connection Settings'. If that doesn't work (or you don't want to reset) then I think you need to use the service menu to go to 'Picture adjustments', 'Picture service menu' and then 'Geometry adjustments'.  But be careful making adjustments - note the initial settings and take photos so that you can restore back to what you currently have.

Thanks for the info Guy! I didn't remember resetting anything in the monitor settings so I had a ferret around in the options. Found the problem, it was in the TV setup section, because I have terrestrial and also satellite digital I need to have both options 'ticked', somehow the terrestrial option had become unticked, I re ticked it and yes in the Picture list the size option had reappeared  so an easy job selecting the correct picture size! Just discovered the same problem with my 10-32, same solution brought a resolution! Now a happy bunny again, have been building a 1:12 scale Pilot launch recently, or finishing it off after the covid debacle etc so now hopefully back to things B&O Tony