Update & conclusion; Purely by coincidence, just the other day, I was relocating a spare bedroom TV from stand mounted to wall mounted when I noticed it had a satellite reception socket, allowing me to conduct some diagnosis by substitution. With TV selected as the input source, and a DMM connected...the socket powers up and provides 18.5v. I connected the TV to the satellite antenna, and it accomplished an autotune OK, with none of the nonsense about asking for a postcode, despite never having been connected to the antenna before. It discovered 761 channels, and did exactly the same on the other second LNB connector. I sample viewed a few channels, all fine. On that basis it seems both lanes of the antenna system are fully operational, therefore the fault must lie within the Humax Foxsat receiver, and it's inability to supply power to the antenna.
Can anyone recommend a good company for repairing Humax receivers, as Humax don't deal with this model anymore? Cheers, Allan