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[Chancer]

QUOTE

The original lens is glass & during the recording process as the laser heats up the surface of the disc being written & ,a very small amount gas is given off.This has an ageing effect on the lens it also efects the ability of the optical block to focus & maintain tracking.Hence playback problems.

Quote from the technical bulletin from Philips re DVDR880

You seem to be missing the point here if as you say the Laser unit never fails can you explain how hundreds of customers would pay me for a replacement laser fitting to there machines which incidentally cures the problems. I see it every day. Fact Laser assemblies go faulty and do not last indefinetely. I could maximise my profits if that were the case so I could charge more labour for throwing in a cheap sled motor or spindle motor.

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The lens itself does not "cloud" if it's optical glass which is what is used in DVD/CD's. That's the whole point of coated optics, to eliminate this type of thing.

From your previous reply

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In so called "worn out" units I've taken apart this is completely fogged over

Obviously you need to check this fact and not just look at a spec sheet on this and strip a few more units to see that this does happen. Again reference to the technical bulletin.

QUOTE

The pot does NOT adjust the focus. Check the specs for the assembly and you'll see that it merely controls the pickup. The current output to the laser itself is fixed.

Anybody who adjusts a pot based on a resistance reading should not be doing it to start with. Everything we set up is done with the correct equipment and using a disc supplied (at high cost) specially for checking the Focus of the Laser.

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If the output levels on your VCR units are decreasing then it is more likely that there are other factors at play, such as low current supplies. I wouldn't call this exactly a good example as there are too many variables.

This is utter rubbish. If the end sensor does not pick up the output from the  cassette LED and changing it for a new cassete LED rectifies the problem how can the cause be another factor. If it was then changing the LED would still not cure the problem.

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I remember reading about it some time ago, (though please post it if possible) If I remember correctly while the terms Wear and Laser Assembly came up, it was NOT that the laser "wore out" but there was a problem over time that affected the entire unit

Again incorrect the problem I am referring to is specifically the Laser not the associated mechanical bits although I am in no doublt that these fail.

As I did say worn out is probably not the correct wording but ask around all the other qualified technicians that run service centres and I am afraid you will get the same answer that laser units can and do fail. Yes we all know problems arise from foriegn particles on the outside of the Lens which can easily be cleaned but this should not affect the inside of the sealed optics yet when stripped down the problem is very evident.
On the subject of the thomson drives I have personally not come accross a problem with them in the xbox. Changed a few lasers on PS2 machines though and cured the problems by doing it and they do not come complete with any of the associated mechanics.
I assumed you were reffering to the inside of a CRT with the statement regarding the milky effect. But airborne dirt on the outside of the glass is hardly a comparison to the external lens surface on the laser. the same could be said about anything " My fire surround or my windows pick up dirt as would anything.
I still stick to my statements taken from having to repair the things every day of my life.
Its a rubbish job by the way but  I love debating some of the finer points and the differences of opinion and experience still interest me.

Added Edit
Direct quote from Panasonic Technical bulletin regarding product group DVD with reference to DVD A100. revision 1 Quoted at head page of Technical Spec
"OPU life expectancy:Between 3000 and 5000 hours average."
What lasers do not fail??

[opjose]

Re: Bullitin

Yup it gives off gas as stated, but it DOES NOT cloud the lens, it coats it.

The "gas" (if you check it's makeup) cannot etch or corrode the glass.

That report mistated this as an "aging" effect, wherein you are getting this erroneous impression that it is actually AGING.

IT IS NOT!

It is being COATED. Not the same thing.

The "customer" logic doesn't apply.

If the optics get fogged over your replacement would indeed help, but it would be equally expiditious to merely CLEAN the optics, as it would have EXACTLY the same effect. The problem is that you cannot easily reach both sides of the lens or the reflector.

And yes I've stripped apart plenty of units and worked with lasers for quite a long time in many areas.

"you explain how hundreds of customers would pay me for a replacement laser fitting to there machines which incidentally cures the problems."

In effect you are replacing something which does NOT need to be replaced, rather since it's easier to perform an assembly change (it is rather monolithic is it not?) the laser is co-incidental. If it were seperated from the optics, there would be no need to replace the laser, just the optics... better yet they could be cleaned... except the cost of labour would not justify the expense.


"Anybody who adjusts a pot based on a resistance reading should not be doing it to start with. Everything we set up is done with the correct equipment and using a disc supplied (at high cost) specially for checking the Focus of the Laser."


WOW do I agree with this!

I've been highly critical of the so called "pot tweaking" as advocated here. It tends to do far more harm than good!!!

However the "pot" does NOT adjust the focus or intensity of the laser. It merely adjusts the sensitivity of the receiver circuitry to noise.

Check it out since you don't believe me.


"This is utter rubbish. If the end sensor does not pick up the output from the cassette LED and changing it for a new cassete LED rectifies the problem how can the cause be another factor. If it was then changing the LED would still not cure the problem."

I have no experience with your VCR problem so I can't really speak to that.

I do have experience with LED lifetimes and characteristics and it is EXTREMELY difficult to get them to fail. You MUST push them to do so.

I don't know what is going on with your VCR stuff, but given the characteristics of most LED's the most likely cause remains that it is something other than the LED itself... your insistance not-with-standing.

"This is utter rubbish. If the end sensor does not pick up the output from the cassette LED and changing it for a new cassete LED rectifies..."

Call it rubbish all you want, but I have to deem your assertion to be in error, considering that you can find REAMS of information about LED longevity anywhere. And very little bear out the output degredation you cite outside of your VCR experience (giving you the benefit of the doubt on this...).

Again this is one of the key characteristics that endeared LED to the electronics world. That they had rather incredible lifespans and stability.


"Again incorrect the problem I am referring to is specifically the Laser not the associated mechanical bits although I am in no doublt that these fail."

If you are citing that Phillips release, then you are talking about something that misrepresented the problem to begin with. The laser in the Phillips case, DID NOT wear out, even though Phillips incorrectly alluded to "aging" in the release.

The glass is not AGED, it is COATED (as I've previously indicated happening with assemblies I've torn apart) by detrious. In this case the overly close proximity of the Phillips assembly exacerbates the gas expulsion problem to the point that the drives were being prematurely affected. THAT was the problem with the read/players which was later rectified by simple mechanical means. E.G. increasing the clearances.

And NO, the laser units DO NOT "fail" unless they are pushed electronically to do so. You have to work hard at it too.

The lifespan of these things approaches a millenia with almost no change in output levels and frequencies. That is why laser repeaters are buried at the bottom of the sea.

You could go on about how you've changed laser assemblies and this improves things. I don't discount this EFFECT, but the problem is not the frequency of laser activation or utilization rather that something "other" than the laser is usually to blame, and in changing the assembly you've corrected it.

E.G. case in point the Phillips example, changing the assembly results in "clean" optics and focus, hence improved performance.

You say

"Yes we all know problems arise from foriegn particles on the outside of the Lens which can easily be cleaned but this should not affect the inside of the sealed optics "

But thereing lies the rub!

The optics are -NOT- all sealed. That is the laser has a clear cover, but the lense itself is held seperately. Both sides are often exposed to the air as is definitely the reflector.

Escaping gas and plastic detrius (as in the Phillips case) is very likely to coat all of this.

While the end effect is decreasing performance, stating that the laser "wears out" gives a very wrong impression to people here. There is already a perception that people should not use their DVD drive's lest they cease to function.

Hmmm I have an unused Thompson that works as poorly as a used one, while older and more utilized Samsungs hold up very well. Clearly something else is amiss.

These things SHOULD work for a very long time given NO mechanical failures.

[Chancer]

[opjose]

QUOTE (Chancer @ Jun 5 2004, 12:05 AM)

I can see what you are driving at but  despite what is supposed to happen and what is quoted in spec sheets the reality is far different. You are wrong on the Philips issue, the problem was resolved by changing to a plastic lens. No disrespect as you obvioulsy are well versed in all this stuff but I tend to take what the manufacturer calls ageing as being correct (premature ageing). If the problem caused to the inside of lens can not be addressed by cleaning then that has to be failure of the OPU. Not sure if you saw the edit but why would Panasonic quote a life expectancy on these? What i am saying that if failure of the laser Unit cannot be cured by external cleaning methods then whatever within the laser unit is the root cause has no real bearing as the unit must be replaced as it has failed, This failure is more likely the longer the unit has been in use. If the coating on the lens is caued during use then the more use the worse the problem. We see very few failures in this respect on new equipment but more as the equipment gets older. Guess we will have to disagree on it. I bet the original poster having read all this has thrown his xbox at the wall now . Just in case not buy a secondhand Samsung drive

I can find you link after link which will tell you that the failure of CD/DVD units is close to NEVER due to laser or optics failure or aging, even posted by researchers who take the MTBF specs with BIG grains of salt.

The spec sheets are not wrong. Typical laser life spans range in the order of 12 YEARS of continuous use. Typically 100k+ POH.

Even halving that figure results in durations greatly in excess to the age of the Xbox itself.

Interestingly enough the more the laser is kept ON the better, as "damage" to it is diminished this way. These are not my findings or assertions, and it contradicts, "failure is more likely the longer the unit has been in use".

Phillips is wrong to use the term aging. If you read their original release on this problem you'll find that they refered to it as an "aging effect", which is what seems to be causing your assumption that there is degradation to the glass or assembly.

If anything their solution in switching to plastic may have been prompted by lesser adhesion, not by clouding. (glass is not a very permeable substance after all.)

Their quoted life span is in effect irrelevant to this discussion, their unit has an inherent problem which makes it's effective "life span" or usage window,  subnormal. Had it been properly designed it would have been no different than any other similiar device.

"What i am saying that if failure of the laser Unit cannot be cured by external cleaning methods then whatever within the laser unit is the root cause has no real bearing as the unit must be replaced as it has failed"

In effect you are saying that the end effect is the same.

Yes, but only in a limted sense, as the problems seem to be somewhat confined to the Thompson drives on the Xbox, and not other similiar DVD/CD's on the market.

Heck I was involved with the "great HP class action suit" because their CD drives did not hold up very long (mechanical problems), and when they failed produced subpar capacities, yet these exceeded the performance and lifespans of the Xbox drives.

If as you allude, "all" DVD/CD's degrade so quickly due to laser/optics aging problems the lawsuits alone would be voluminous, forgetting the RMA's & returns.