Re: anyone know where I can find a service manual for Disk II

["Michael J. Mahon" <mjmahon@aol.com>]

Silicon Sam wrote:
> On Apr 10, 12:16 am, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> > Silicon Sam wrote:
> >
> > > On Apr 9, 6:26 pm, Mike Willegal <m...@willegal.net> wrote:
> >
> > > > Hi Michael,
> >
> > > >       Are you sure about the analog recording thing?  I was speculating that
> > > > whole track was simply written with some repeating pattern like 1s and
> > > > 0s.  Last night I was looking at the signals coming from a regular
> > > > formatted disk  and it shows many of the same patterns that are seen in
> > > > service manual, with a lot of added noise and jitter. I figure that the
> > > > noise and jitter came from the sector headers and actual data not being
> > > > a consistantly repeating pattern.
> >
> > > > Regards,
> > > > Mike Willegal
> >
> > > > Michael J. Mahon wrote:
> >
> > > > > Mike Willegal wrote:
> >
> > > > > > Hi Tom,
> >
> > > > > > Perfect,  just need to find or make a good alignment diskette.
> >
> > > > > Finding may be easier--it's an analog recording!
> >
> > > > > -michael
> >
> > > > > NadaPong: Network game demo for Apple II computers!
> > > > > Home page:  http://members.aol.com/MJMahon/
> >
> > > > > "The wastebasket is our most important design
> > > > > tool--and it's seriously underused."
> >
> > > The cats-eye signal was written on a floppy by a machine that had a
> > > wobble between tracks 15 and 17 (or whatever two tracks) and that way
> > > you had a perfect sine wave on your scope on track 16.  As I recall
> > > Dysan charged $50 each for them floppies back in the late 70's early
> > > 80's.  I wore out and messed up a few of them.
> >
> > That sounds different than the alignment patterns I saw--
> > maybe there were multiple approaches...
> >
> > How fast was the "wobble"?
> >
> > -michael
> >
> > NadaPong: Network game demo for Apple II computers!
> > Home page:  http://members.aol.com/MJMahon/
> >
> > "The wastebasket is our most important design
> > tool--and it's seriously underused."
>
>
>   Not sure, but since the sine wave was a slow one, I would say it
> only had to wobble once per revolution.  The object was to write a
> signal from 1 track to the other, and measure the track in between.
> Obviously the disk can sit still and the head move back and forth
> between tracks while writing.  But it would have to be a mechanism far
> more precise than the cam that Shugart and Alps used.
>
>   Yes, there are several signals on the disk, this is just how they
> made the cats eye recording.

I'm having a hard time seeing how a wobbled recording makes a
cat's eye diagram.

It seems like the display would be amplitude modulated at the wobble
frequency when off-center in either direction and amplitude modulated
at twice the wobble frequency when on-center, assuming that the
amplitude of the wobble was a bit more than a track.

And I agree that this would require a special drive to record--
either one with a voicecoil actuator or (kind of fun) one with
an eccentric spindle.  ;-)

The dual-frequency recording I described could actually be made
in a non-phase-coherent way, with a single headed drive.  One
frequency would be recorded with the track positioned +0.75
track, and the other at -0.75 track.  The only problem would
be ensuring that the edge of the erase head on the second track
written didn't put the "equal amplitude" point off the center
of the nominal track.

-michael

NadaPong: Network game demo for Apple II computers!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it's seriously underused."