As a hobby,I try to repair media for the local library :audio tapes,(Books on tape),VCR tapes ,CDs and DVDs.
Scratches on pressed,commercial disks are a problem with
careless patrons using a variety players.
I first inspect the disk against a bright light to see any holes.When cleaning disks,I cut a tissue in half ,fold each twice into a pad and soak it with iso-propyl alcohol or,if not available,some 91% rubbing alcohol(NOT 71% with resins).
Then start rubbing from center to edge ,all around,especially on scratches.I start playing CD’s and work on something else nearby,listening to the low volume for problems.If a problem shows up,skips or stop,I note the information on the display.
I play DVDs on my $30 Norcent DP315 player at 4x normal speed.If a scratch is bad enough ,the picture freezes.
Then I start to polish the scratches .
I repeat the cleaning step,pressing hard.If no help,I try a variety of methods.I bought a Memorex Optimix Pro,a motorized cleaner with brushes and a white paste abrasive
(suspect aluminum oxide).The vinyl tube of paste was half empty.I know that solvents will diffuse through vinyl over time .I keep my used caulking cartridges in tightly sealed plastic bags to prevent hardening.
Most of the time I had NO help with the freeze but a lot of fine scratches.
I tried a brass polish-NO help and made the surface hazy.
Tried Colgate toothpaste and noted that the first ingredient
on the list was “Hydrolyzed silica”,sand.Got he same haze and NO help with the freeze.
One library in our county had an “Eco-Smart” machine from RTICO.com that used a water grinding operation.
The cheapest was $3,000-too expensive for me.I wondered if grinding off the surface of a 5.8 mm (0.050") thick DVD would disturb the focus of the laser sensor,although the salesman said that they had no problems.
Often a DVD would be OK except for one freeze.If I could locate that bad spot ,maybe I could salvage the disk.
I understand that the player motor varies from 200-500 rpm as the Laser advances to the outer edge.
There should be some mathematical way to judge the distance from the center to a freeze point.Right now,all I can do is identify the scene number and compare that to the scene total and guess.
I’ve fixed cracks on the center hole by placing a ring of adhesive tape over the hole and cutting out the 9/16" hole with a hobby knife.I put the tape on a sheet of backing from gummed labels(eay to get off),draw and cut a
1 3/8"ring leaving an uncovered tab for removal.
One case where the edges of the hole were broken,I cut out the center of a discarded disk and glued it over the center of the broken disk.The player wouldn’t let the drawer load.I used a washer of .004" Mylar that worked.
When searching for a bad spot,I had some luck by wetting the surface with alcohol and examining the reflections under a strong light.Once,I found some “rot” where the top of the rot showed as mountain peaks above the alcohol surface.I also look at scratch reflections in the shiny layer.
If I can see them,I assume that they are small surface scratches.
Question:Does anyone know how to calibrate the play time with the distance from the center of a DVD?