Conference cookie::notes$archive:cd_v1

	I have  personally  repaired  damadged  CD's  using,  get this, auto
	polishing compound.   It's  a mild abrasive that removes the scratch.
	I have found that this usually works for very mild scratches.  There
	is a product that was  mentioned  elsewhere  in this conference that
	actually fills in the scratch with  a  similar  material used in the
	disk surface.
	
	Is  this  scratch  circumfrential  (Going with the  data  paths)  or
	radial.  Radial scratches should not cause a  problem with the Sony.
	I have the cdp-750 and have run an experiment (borrowed from Digital
	Audio Review mag) where I place a 1 mm wide piece of masking tape in
	the radial direction on the data side of the disk.  My player didn't
	even notice that.  I worked my way up to 4 pieces,  at 90 deg angles
	from each other, the player kept tracking but I could here the error
	correction glitches.  Most scratches are much thinner then 1mm.  Its
	the ones in the data direction you have to worry about.
	
	Good luck,
	Nick

Nick,

Thanks for the auto polishing compound suggestion.  Unfortunately the scratch
is sort of circumferential in parts which I assume are the sections that
are giving trouble.  The scratch is about 2 cm is length but only 1-2 mm
is actually tangential.
           
I read a paper by somebody in Philips and as far as I know the disk is scanned
at 1.25 m/s.  At 44.1 kHz sampling that's about 70 samples/mm for both
channels.  I'm pretty sure that it handles blocks of 12 audio signals before
adding parity and other nice stuff, so that means we're dealing with sound
quanta of 0.14 mS with each block. And then since the blocks are interleaved by
28 bytes at a time, all this means that the player can handle a 48 frame
burst error i.e. 8.16 mm, the player should be able to interpolate a pretty
large scratch before giving up.  

However this is only in theory and I'm not sure what the SONYs do for error
detection and correction.  What really worries me is the fact that the player
kept repeating the same section over and over again rather than give up and
move on.  Since under normal circumstances the player does not react to the
disk so much as to the user, i.e. fast forward, play, rewind, etc.,  this
repetition seems to be due to some flaw that seems to be making the laser
go back to the same section, i.e. the laser's motion seems to be derived
from the faulty data that it reads.

I will try the filler though, and let you know what happens.

Vijay

    I've experienced skipping CD's a few times.  All but one were do to a
    piece of hair or lint on the disk.  My most recent one turned out to be
    a scratch on a disk I bought used from BCD - that's what I get for
    trying to save a couple of bucks.  I haven't tried repairing it or
    returning it for that matter.  Living in Worcester, I haven't made the
    time to go back to Harvard Square.  Besides, I figured they'd never
    take back a used disk anyway - anyone have any info on their return
    policy. 

    
    My understanding is the used discs at BCD are guaranteed.  If you've
    got the reciept, it shouldn't be a problem - they'll take it back.
    
    
    								-mr. bill

    re: .0
    
        Unless you can't stand the thought of parting with your disk
    for a few weeks I'd send it back to the club and try to get a new
    one.  Once you muck around with the disk and try to polish the
    scratch I bet you nullify your chances of getting a new disk.
    
    ASP

    Another solution (and I may have even got this from an earlier note)
    is to use Toothpaste to polish the scratch.  I have a Stevie Ray
    Vaughn CD which I accidently scratched by hitting the data area
    with the jewel box.  At the same point in the song, it would repeat
    and skip.  It sounded like M-M-Max Headroom.  Anyway, I took some
    Crest Toothpaste (Gel-type, not regular) and smoothed a dab on
    the scratch with a Kleenex.  The scratch disappeared, and the CD
    plays normally now.  
    
    It may be low-tech, but it is an inexpensive way to save a CD.
    
    -Brian
      

I called the CBS CD club and they said that they'd send another copy so I guess
I don't get to try fixing this disc.  By the way they're much easier to deal
with on the phone that by mail.  Their number's (812)466-8125. 

I'm now toying with the idea of getting 3 free CDs from them, buying 2 at
regular prices, and closing my membership in one letter.  Should cost about $35
for 5 CD's and I wouldn't have the problems of trying to cancel later.
Comments/suggestions welcome. I still haven't found 5 that I like so if
anyone's interested in pooling in send me mail. 

-Vijay

    I tried, on consummer reports recommendation, to use "Glass Wax"
    for damaged cd's. [The stuff that turns white on your windows] 
    So far it has worked very well.
    

    Even PLEDGE WAX works real well...practically any type of soft wax
    should work.  It just fills in the scratch and away you go.

    A friend of mine has used Butcher's Wax (the paste type) with success
    after toothpaste and auto wax failed on a horribly scratched CD
    (purchased at BCD by the way).  I have had limited success with
    toothpaste (Crest and Colgate anyway) - be sure to "polish" the CD in
    the radial direction. 
    
    Since the music doesn't seem defective, just the order of the music,
    the probable reason for .0's player sticking on one particular area of
    the CD is probably a tracking problem as opposed to an error correction
    problem.  If the laser and servo can't stay on the spiral of bits on
    the CD surface no amount of data error correction will help the
    tracking.  The CD player doesn't used the encoded time/track numbers to
    stay on track.  The scratch is causing the player to jump (back) one or
    more "tracks" to the inside. 
                                 
    GAS

    I have to issue somewhat of a retraction on my reply in .3.  I received
    a CD care kit for Christmas (brand name 'Bib') and decided to give the
    CD cleaner a whir on my 'scratched' copy of UB40's "Rat in the
    Kitchen".  Well, the isopropanol spray combined with the cleaning pad
    removed the 'scratch'.  Apparently there was a small amount of gunk on
    the CD that looked like a scratch.  I put it in the player and it
    sounded as good as new (pretty good for a used disk, eh!).  Even if I
    never have to use the cleaner again it at least saved me a trip back to
    Boston.  Apologies to BCD. 

    As a footnote, my wife bought this CD care kit at Lechemere.  It has a
    holder for the CD, a spray bottle of isopropanol, and a cleaning pad
    that rides gears in the CD holder which ensures that the wiping is done
    in the proper manner.  Also included is a soft cloth for cleaning the
    CD player cabinet, a long barreled air brush (like in camera lens
    cleaning kits only longer), and cotton swabs for cleaning the laser
    lens. 

    I had a CD that I left at a friends house, his son set it on top
    of a mesh top cage where it got very badly scratched.  I buffed
    it out with a bench type buffer and polishing compound.  This
    CD now plays perfectly! 
    

    Hmm, can I borrow that? I have a "Momentary Lapse of Reason" that is
    marked, but plays ok on my AIWA, but skips on my D-4...