CED Digest Vol. 3 No. 10

CED Digest Vol. 3 No. 10 • 3/7/1998
Date: Thu, 05 Mar 1998 19:05:35 -0600
From: Geoff Oltmans 
To: ceds@teleport.com
Subject: Cool book

I found a really neat book at the University library here...it was a
book of Videodisc and optical storage (in fact, I think that's what the
book was titled). It contained very in-depth information about various
formats...including CED! There were two chapters specifically for CED,
which contained information on VHD as well. The information was very
technical, including information on stylus dimensions, mastering
techniques, tracking control, etc. etc. I'd say a good 30-50 pages
covering CED.

*Geoff!*

-- 
Geoff Oltmans - CPE Undergrad University of Alabama in Huntsville
KERNAL = Keyboard Entry Read Network And Link
http://home.sprynet.com/sprynet/geoff

------------------------------------------------------------------------
Date: Sat, 07 Mar 1998 00:07:57 -0800
From: Tom Howe
To: ceds@teleport.com
Subject: RE: Color Shifts on RCA F and G players

On Thu, 19 Feb 1998 c1803 wrote:
>I recently purchased 160 CEDs and a SFT100 at a flea market. Although there
>was no way to test the equipment, the discs were in original shipping boxes
>(about 8 to a box) and the outside of the player seemed pristine (and
>included the styrofoam shipping "covers". Now the bad news: while discs
>play well, any color (even on the logos at the beginning of b&w discs)
>constantly fades in and out. During the time it changes from color to b&w,
>the picture distorts.

These color shifts are usually the result of variations in the 450RPM rate the
turntable needs to spin at. The Turntable Speed Check Strobe available in the
tech info section at CED Magic can be used to check on this. Some players I've
seen will play normally at the start of play and then start the color shifts
later on. This is because the players have a limited ability to correct for
speed variations with their time base correction circuitry, but as the stylus
moves closer to the center of the disc the groove circumference continues to
decrease, and at some point the decreasing signal bandwidth gets too narrow for
the correction circuit. 

RCA's F and G players seem particularly susceptible to this because of the 16
pole magnetic ring in the base of the turntable. Damage or weakness in any
one of these poles is enough to throw the rotation rate off. I've looked at
turntables that have undamaged magnetic rings, but still rotate unevenly, and
believe it is due to weakness in the magnetic field strength due to age, which
means this could eventually be an issue with all CED players. It already has
affected all the Sanyo players I've ever seen, which all exhibit the same
characteristic- the turntable won't spin up after a disc is inserted. But if
the turntable is given a little nudge after loading the disc it will spin up
and play normally. The strength of the magnetic field in the permanent magnets
has decreased to the point that the electrically generated fields produced by
the motor cannot overcome the inertia of the stationary turntable.

RCA's J and K players as well as the Hitachi manufactured units also depend on a
magnet to get the turntable spinning. I haven't yet seen any of these units that
won't spin up due to a weak magnet, but these players use a simple toroidal magnet
that can be replaced or possibly remagnetized.

--Tom Howe
http://www.cedmagic.com

------------------------------------------------------------------------
Date: Sat, 07 Mar 1998 15:31:37 -0800
From: Neil Wagner 
To: *CED Digest <ceds@teleport.com>
Subject: Videodisc History Part 17

[sorry about forgetting to post this last week.]

>From the December 1981 "Popular Science"
by William J. Hawkins

VIDEODISCS - new alternatives to movies at home -- Part 2
---------------------------------------------------------
  The CED units are basically no more complicated than an
audio record player.  A turntable spins the record, a
stylus tracks the grooves to extract the audio and video
information.  (The stylus is rated for about 500 plays
and can be replaced in minutes at home.  Cost: about $75.)
  The only delicate piece in the system is the record it-
self.  Scratches or fingerprints could destroy your movie.
To prevent it, the CED records come in a permanent plas-
tic jacket.  You slide the record--jacket and all--into
the player.  Then you pull the jacket back out.  The
record automatically stays in place on the internal turn-
table.
  Because it is a record-in-a-groove system, you can't
instantly scoot all over the disc.  It takes a bit of
button-pushing.  The basic RCA model gives you two fast-
forward and two reverse speeds.  But you don't see the
picture while using the fastest speed (approximately 120
times normal).  Instead, a visual indicator shows the 
approximate minutes into the disc.  The type of indicator
used varies with the machine.  Radio Shack, for instance,
uses a sliding wand on a time scale (like tuning a radio).
RCA, Zenith, and Sanyo use a digital display.
  Once you're near the area of the show you want, you can
"home in" with the slower-speed button (16 times normal
speed).  Now you get to see the picture, and with practice,
you can stop within a scene or two of where you wish to be.
  There are some variations to all this.  Some brands, such
as Hitachi and Sears, have cut the fast search down to 60
times normal but allow you to see the picture in both
speeds.  And still others, such as Toshiba, have two slower
speeds with visual search and a third high speed (130 times
normal) you use with the digital display.
  Still-framing is a bit of a problem on CED machines since
each revolution of the record contains four separate frames
of picture information.  The result of the Sanyo machine is
a shaky still-framed picture (unless all four frames are
nearly identical).  The problem is solved another way by
most other CED systems:  they **don't have** a still-frame
button.  They have a PAUSE button that blanks the TV image.

[stay tuned for the final part of this article, including
 a comparison table of various models...next week]

-- 
Neil - nw@ix.netcom.com
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