Backing Up VHS

[apples]

Hi all,

Newbie here, wonder if any of you can help.

I recently purchased a philips DVD Recorder, and i want to record some old vhs tapes to dvd, the vhs tapes are mostly documentaries i recorded from the TV years back, but when i try to copy, i get a picture for roughly 10mins, then it just goes black and all i get is sound.

Any ideas??

Thanks