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* Magic <[EMAIL PROTECTED]> on Wed, 13 Oct 1999
| If the front laser becomes mis-focused the head assembly moves vertically
| keeping the main read head a fixed distance from the CD at all times. The
| three laser system also allows slight horizontal movement to keep the read
| head focused in the center of the track.
Which does you no good if the read laser is the one out of focus. The two
tracking lasers will gladly move the head to where they think the read
laser should be -- which is anywhere but where it should be.
| So why if I have a scratched CD that wont play in my Marantz unit (Phillips
| mechanism) do I have to put it in the Sony (Sony mechanism) to play it
| without it skipping?
Skipping as in physical shock, not as in dealing with damaged media. As
for why it does not work, I dunno. Maybe a fluke. Don't scratch your CDs.
| And why did the Phillips guy on Open University sit and explain at length
| how the tri-spot laser system worked, if in fact their system only uses one
| laser?
Because for every Phillips mechanism sold, some 50 to 100 Sony mechanisms
are sold.
| According to what he was saying, one laser alone would be useless because
| it would not be able to compensate for slight variations in the CD. 99%
| of the time a CD is never in the absolute dead-centre of the center
| spindle anyway, so without a tri-spot system it wouldn't play because the
| laser would keep missing the centre of the track and would be unable to
| read a continuous data stream..
The single laser does both reading and tracking. As I said, the logic is
that if the laser sees that it is not properly aligned, it tells the motor
to align itself correctly.
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