Optical discs and magnets - Page 2 - AVS Forum
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post #31 of 43 Old 02-26-2012, 10:13 PM
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Quote:
Originally Posted by greaser View Post

Iv'e never seen this question asked before,so i thought id'e ask it now.
Can a disc with something recorded on it be damaged by placing it tooo close to powerful magnets such as the magnets in audio speakers or electro-magnetic fields?? Reason i ask is cuz iv'e noticed some of my TY disks going bad(skipping,sticking on one spot and refusing to play any further) after about a year and a half,and am wondering if my practice of placing discs(in their cover) on top of my center speaker for up to 2hrs.before i actually plan on watching them 'could' be the culprit??

hi greaser...

i know most folks might not agree with this, but clean the optics in your machine...

it's a nuisance, but it could make the difference...

rgds,
ron g
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post #32 of 43 Old 02-27-2012, 05:26 AM
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Originally Posted by kjbawc View Post

Oops! I was talking 150 Fahrenheit. I've worked with polycarbonate sheeting, and acrylic. They might begin to melt, or take a permanent bend, at 150C, but I'm sure they will warp at a much lower temp. If I only had some coasters, I could experiment...

Yeah, I wasn't attesting to the merits of the 150C quote, just that you accidentally converted from celcius to fahrenheit.
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post #33 of 43 Old 02-27-2012, 06:48 AM
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Polycarbonate has a heat deflection temperature of 140°C. It will not deform at lower temperatures.

- kelson h

The bitterness of poor quality lasts long after the sweetness of the low price is forgotten . . . life is too short to drink bad wine

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post #34 of 43 Old 02-27-2012, 01:26 PM
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Quote:
Originally Posted by greaser View Post

Hi kjbawc, it's not from bending discs cuz i'm real careful 'bout that,and if the failures were caused by bending,then i would been having failure problems all along,not an explosion of disc failures in just the past few months.
My best guess is that one or more of my orders for discs(T-Y 8X -r) contained a whole buncha flakey discs that fail over time(8mos.-2yrs.)and they've only recently begun to show themselves.Either that or disc manufacture quality has taken a hit.So far as i can recall,none of my Verbatim DLP discs has failed,only the T-Y's.My question about magnets affecting discs is a reaction to an unfortunate co-incidence that has clouded the waters and caused unnecessary confusion and embarrassment for me.

It is quite possible that you have stumbled on a bad batch of disks. I had a number of JVC T-Y disks fail, and oddly enough, every on the the cake box that failed, did so at exactly the same point on the disk (as measured by the EHxx in terms f how much has been written to the disk in a percentage). All six of the ones that failed, did so at the same percentage. I changed from maximum speed dub, to what the Panasonics call Silent Mode, which I think is 4x rather than 8x, and the problems went away. I now use silent mode on all my recorders. The time savings is not significant enough to make it worth the gamble of a bad burn.
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Originally Posted by Super Eye View Post

I certainly wouldn't advise anyone to place optical discs into direct sunlight. With long-term exposure you risk the dye fading. Last summer I left some unlit taper candles by a closed window in my home on a hot day - when I got home the candles were bending. I sure wouldn't risk that kind of exposure to my archives on optical discs. Some here may argue that there is no evidence of discs going bad if exposed to direct sunlight - that's fine, my only argument back is my archives on optical disc playback just fine with my storage and handling methods.

The Navy did a study, and I can assure you that they found direct sunlight will cause otherwise good disks, that have been properly written to, to fail in a very short time, regardless of the brand (they used a half a dozen disk brands labeled "archive quality").

If I were to make an off-the-wall guess as to the issues you are having, it COULD be, and I don't know if what I am suggesting is even possible, so I will be corrected if I'm totally off base here, that the laser in your mahine is getting old and losing intensity, or at the very least, the power supply board is going out of spec, and the laser is losing intensity. Again, just a wild guess.

Luke

Evil is charming and beautiful. It makes you doubt yourself. It asks for one small compromise after another until it whittles you down, and it functions best when no one believes in it.-JOA
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post #35 of 43 Old 02-27-2012, 05:52 PM - Thread Starter
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^^^ Geez luke, that comment you made about a dying(or mis-aligned maybe??) laser is one of the things i fear most,and am trying not to think about! I'm not really worried about the laser dying because i don't think that the laser in machines that are ~ 2yrs.old or less and are lightly>moderately used would have that problem.I hope there's no power supply problem either(that was my 2nd.fear). Id'e much prefer to have a bad batch of discs than either of those 2 problems. Also,if there were a laser or power supply problem,then i should be seeing failures with my Verbatim (azo)DLP discs,but as far as i can recall,only the T-Y discs have failed. but who knows??,only time will tell if the Verbs.will also show failures.
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post #36 of 43 Old 02-27-2012, 06:44 PM
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Quote:
Originally Posted by Kelson View Post

Polycarbonate has a heat deflection temperature of 140°C. It will not deform at lower temperatures.

Well, I'm going to have to try some experiments this summer. But, I don't think that heat deflection temp. has much to do with warping in the sun, or heat. We aren't talking about melting, or deforming from becoming soft. The real question is the linear thermal expansion coefficient. Uneven heating, and expansion, it what causes plastics to deform. They generally stay deformed, even when they cool. LPs are notorious for that, but they don't have the durability of polycarbonate. I have installed enough acrylic and polycarbonate sheet windows to know that they will expand, and bulge, in direct sunlight in the summer, unless they are given plenty of room to move.
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post #37 of 43 Old 02-27-2012, 07:38 PM - Thread Starter
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Quote:
Originally Posted by Super Eye View Post

I certainly wouldn't advise anyone to place optical discs into direct sunlight. With long-term exposure you risk the dye fading. Last summer I left some unlit taper candles by a closed window in my home on a hot day - when I got home the candles were bending. I sure wouldn't risk that kind of exposure to my archives on optical discs. Some here may argue that there is no evidence of discs going bad if exposed to direct sunlight

An interesting experiment testing for sunlight damage would be to set out a couple of discs in the sun on a cold winter day when heat is not a factor in disc damage,then you could probably get a much truer test on how long it takes sunlight alone to damage a disc.I think that would be much more interesting than figuring out than at what temp. a disc will warp,or melt.
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post #38 of 43 Old 02-28-2012, 11:00 AM
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hi folks....

please don't take this in a bad way, but i felt i had to comment with my 2 cents worth...

DVDs ( non-rewritables ) work by using an infrared light beam to change the dye layer... this is light, albeit infrared...

SUN = LIGHT ( including infrared light )...

even though sunlight is unfocused, ANY exposure of a DVD to an infrared light source WILL cause degradation and/or ultimate failure over time... it's simply a question of how much exposure the DVD is subjected to...

while very weak, even prolonged direct exposure ( maybe years for all i know ) to a TV IR remote control could degrade a DVD to some degree...

DVDs are like film. if you expose them to a light source to which they are sensitive, they will be ' exposed ' and affected in some way... DVDs are not re-writables, and once exposure has occured, the dye layer is affected.

rgds,
ron g
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post #39 of 43 Old 02-28-2012, 12:19 PM
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^^^ that was my thinking as well, rkg
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post #40 of 43 Old 02-28-2012, 12:48 PM - Thread Starter
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Quote:
Originally Posted by rkg22 View Post

hi folks....

please don't take this in a bad way, but i felt i had to comment with my 2 cents worth...

DVDs ( non-rewritables ) work by using an infrared light beam to change the dye layer... this is light, albeit infrared...

I know that a red laser (infrared)is used to change the dye layer when writing to dvd discs,but i would also think that more energetic wave lengths such as blue,indigo,violet,and especially ultraviolet would be much more damaging,much more quickly than infrared and probably wouldn't last more than a couple of hours at best when placed in direct sunlight. Right?? wrong???
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post #41 of 43 Old 02-28-2012, 01:12 PM
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Quote:
Originally Posted by greaser View Post

^^^ Geez luke, that comment you made about a dying(or mis-aligned maybe??) laser is one of the things i fear most,and am trying not to think about! I'm not really worried about the laser dying because i don't think that the laser in machines that are ~ 2yrs.old or less and are lightly>moderately used would have that problem.I hope there's no power supply problem either(that was my 2nd.fear). Id'e much prefer to have a bad batch of discs than either of those 2 problems. Also,if there were a laser or power supply problem,then i should be seeing failures with my Verbatim (azo)DLP discs,but as far as i can recall,only the T-Y discs have failed. but who knows??,only time will tell if the Verbs.will also show failures.

I wasn't trying to scare you, just trying to come up with a possibility. The power supply issue is most likley easily fixed (if that's the problem). The laser pickup, not so easily dealt with. In two years of light use, not likely, but possible. I'd suspect the disks first, like you did.

Luke

Evil is charming and beautiful. It makes you doubt yourself. It asks for one small compromise after another until it whittles you down, and it functions best when no one believes in it.-JOA
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post #42 of 43 Old 02-28-2012, 01:24 PM
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Quote:
Originally Posted by greaser View Post

I know that a red laser (infrared)is used to change the dye layer when writing to dvd discs,but i would also think that more energetic wave lengths such as blue,indigo,violet,and especially ultraviolet would be much more damaging,much more quickly than infrared and probably wouldn't last more than a couple of hours at best when placed in direct sunlight. Right?? wrong???

absolutely, this is quite possible. i'm certainly no expert, though, and it's quite possible that the dye in the discs would be sensitive to other light wavelengths...

indeed, although not pertinent, every digital camera that i own with a CMOS sensor serves as my convenient ' remote control ' tester, as these sensors WILL display the infrared light emitted by an IR Remote. note that this is a handy test if you think your remote is either not working or has dead batteries...



rgds,
ron g
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post #43 of 43 Old 02-28-2012, 01:26 PM
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one more note, here...

none of this may apply to RW discs, since they are a horse of a different color ( as it were ) since some sort of phase change layer is used to write to these guys. i must assume, though, that since the mechanism used is still ' light ' , these RWs might also be affected to some degree, either greater or lesser.

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