Roger R formulated the question :
Thanks to the replies,
To answer your points:

The fuse glass is perfectly clear, no violent blow. But it is blown.

In that case my first step would be to replace the fuse and see what
happens - it just be a faulty fuse which has failed.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk