| QUOTE (thedustycelt @ Jun 3 2004, 03:40 PM) |
We have discused this before...
http://forums.xbox-s...T&f=41&t=219223
If the diode dosn't age, and the lenses don't fog over time, then why does boosting the powere to the laser work somtimes? Why does replacing the laser work? Somthing is dying with time and use in the laser mechanisim.
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Since you cited that thread, I'll post my answer to it here...
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WRONG WRONG WRONG!
These lasers have glass coated lenses.
Take one apart and see.
Adjusting the pots DOES NOT boost the power to the laser, it adjusts the relative noise rejection of the pickup.
This changes it's noise floor nothing else. It doesn't "boost" anything.
Because of the way in which these things work, actually increasing the voltage would produce little or no result, up to a point in which it would stop working altogether much like a transistor circuit. To increase the output you must INCREASE THE SIZE of the excitable media. This is pretty basic laser theory.
In other words, to pump up the light output voltage does nothing you need more state change materials.
Think of a diode laser in the same manner you would an LED. In normal use an LED will theoretically NEVER "wear out". You could BURN IT out by supplying too much voltage but that's about it.
If you've noted a difference or change over time it is far more likely to be
a ) Mechanism wear, causing the drive not to position the lense in the same place
b ) Clamping mechansim not seating the drive properly
c ) Binding or movement striction causing the stepper not to position properly
d ) Debris (yes including debris on the lense itself)
e ) Changes in the pickup... (pot tweaks strike back!).
f )
I've taken many units apart and one thing which IS consistent, (but NOT "wear") is that often the optics will pick up a glaze over, normally due to changing evironmental conditions.
In the same manner that a TV picture tube attracts ions to it's surface the excited state of the glass optics does the same thing, leaving a milky "coating" on the surface of the reflector or focus lens.
The problem is that while the lens is visible the, reflector (a small 90 degree prism) is buried in the plastic to prohibit it from moving.
In so called "worn out" units I've taken apart this is completely fogged over.
YES it can be cleaned but doing so means that you'll destroy the assembly.
A nice new assembly has no such material.
However this build up is GRADUAL (exacerbated by changing humidity it seems) and not directly related to use.
This is why sometimes replacing the assembly produces a positive result, but in so doing you have or may introduce bigger problems with alignment.
If it weren't for the IMHO "shoddy" plastic guide assemblies and gears, and lack of a mechanism to clean the optics a DVD/CD writer/reader would last practically forever... or at the last until the motor bearings gave out which can take a LONG time if properly designed.
My 12 year old mini-van has never had a problem playing CD's (yeah it's time for a new one) in spite of the fact that the player has been on and playing CD's for all of the 160k miles the vehicle has on it.
Why does it hold up so long?
It's not because of "laser wear" (which is rubbish), rather that the gears and clamping mechanism were made much more durably for vehicles. The lasers were the same type as used nowadays however.
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Topic: Worse Readings (Read 182 times)