Many if not all vcr's reference can be traced to the 3.58mhz color burst
crystal. The vertical frequency divides down nicely to very near 30 hz which
just happens to be the drum and control pulse frequency.
That the 3.58 is critical can be demonstrated by the fact that most vcr's up
until very recently wouldn't even turn the drum if the crystal was bad. I do
think newer vcr's with their improved chips etc, do it a bit differently -
at least that's what I've been told - but I don't troubleshoot too many
$39.00 vcr's for drum servo problems, if you get what I mean. :-)

Mark Z.

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wrote in message
om...
Dear Members: Where can I get (free I hope) a schematic

for any VCR model? Specifically I need a schematic of the

motor control circuit that keeps the main DC servo motor running

at a constant speed....that think they are referenced to a 30 HZ signal.

And, could anyone tell me if the reference is crystal controlled?????

Best to all,

Steven

"Mark D. Zacharias" writes:

Many if not all vcr's reference can be traced to the 3.58mhz color burst
crystal. The vertical frequency divides down nicely to very near 30 hz which
just happens to be the drum and control pulse frequency.
That the 3.58 is critical can be demonstrated by the fact that most vcr's up
until very recently wouldn't even turn the drum if the crystal was bad. I do
think newer vcr's with their improved chips etc, do it a bit differently -
at least that's what I've been told - but I don't troubleshoot too many
$39.00 vcr's for drum servo problems, if you get what I mean. :-)

But keep in mind that this is for playback. For record, the reference
must be the incoming video sync.

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