Recordings are encrypted with a key unique to the box. Only the original box will replay them. Originally Humax would repair the box and posters say the box was returned with recordings intact. Seems Humax now won’t do this anymore.
Other than this afaik no known way of preserving the recordings.
Humax told me they don’t repair anymore as it’s a resister on the motherboard and do they find it cheaper to replace for £55 but they cannot preserve recordings.