VHS recorder problem?

My JVC (HR-J870EK) VHS video cassette recorder has recently developed a problem that manifests itself when recording; a horizontal line appears on the recorded footage when viewed during playback, halfway up the image. On older recordings or pre-recorded tapes, the line does not appear - only on recently recorded footage I have tried cleaning the heads etc, with no success.

Could you please advise me as to the likely cause of this problem.


Regards


G Boothby