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Posted by Jan Panteltje on 08/07/07 21:07
On a sunny day (Tue, 07 Aug 2007 12:44:26 -0700) it happened nobody special
<msu1049321@aol.com> wrote in
<1186515866.196564.325960@e9g2000prf.googlegroups.com>:
>It is not germane that the Umatic signal was "better" than a dub from
>Umatic to DVD, if YOU CAN'T FIND A WORKING UMATIC MACHINE!!!
The Umatic had a basic flaw.
For a moment electronically speaking the demodulator
was a simple one-shot, that produced a pulse of fixed duration every
period of the RF from tape.
In case of a drop out, there would be no pulse(s), and a huge spike would
appear in the video (way bigger then the 1V pp composite) overdriving
everything after that in the video amps, resulting in big white flashes
where the dropouts were.
I fixed one in the seventies for somebody by adding a little oscillator
that normally was synced to the RF from tape, but would run free at black
level frequency when a dropout occurred.
Just a hint if you REALLY want to digitise old Umatic tapes and actually
still have a Umatic.
I no longer have the diagram, but it was a simple 2 transistor circuit
(astable MVB), somebody knowledgeable in analog electronics could design
one I suppose.
If this is too technical you skip it.
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