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Posted by Richard Crowley on 10/06/10 11:32
"Gary Eickmeier" wrote ...
> Thanks Richard. The diagram shows that the audio is the first part of
> the track picked up, not the last. The subcode is the last. But I
> son't see how any part of that scan could be missed by a new head
> drum, especially if you have auto alignment of the scan.
The first part (or the last part) of the scan can be flaky
if the tape wrap around the head drum is not perfect.
The auto-tracking servo averages the whole diagonal
swipe to try to keep everything in sync.
Find a heli-scan machine that you can take the cover off
(or a reel-to-reel machine) and tweak the tape path
slightly to see what happens to different parts of the
picture (and sound).
Those of us who grew up with heli-scan videotape tend
to be continuously amazed that it works so well. This kind
of glitching is notable only because modern technology has
made it so rare.
As for what happens when you replace the head drum
(or do any work to the tape path), whether it will track
previous tapes depends on whether the tapes were written
by a properly-aligned machine (or not). If your re-built
machine has good interchange with other new camcorders,
but won't play back its old tapes, it means that it was already
out of alignment when the old tapes were written. This is not
all that uncommon. It is almost guaranteed with the long-
playing (slow) speed modes. You're lucky if your own
machine will interchange LP tapes.
You have the choice to have them align the transport to
your old tapes, but then it won't interchange with anything
else, or have them align it to industry standards and lose the
ability to read out-of-spec tapes.
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