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In Reply to: RE: Problems Reading CD posted by PAR on May 23, 2017 at 07:52:47
PAR is correct that laser diodes (like all light sources - even the sun) have a finite lifetime. All modern units have a light intensity sensor that adjusts the laser drive current to compensate for diminishing power over time. (Both LEDs and laser diodes fail very gradually, unlike incandescent bulb which fail suddenly.)
However there is another variable and that is the light path. The output from the laser diode first hits a prism so that the beam is reflected up onto the disc. The height of the bumps in the disc is 1/4 the laser wavelength so that when the beam hits an area with a bump that the reflected light cancels with the part of the beam illuminating the flat surface around the bump. This reflected beam travels back through the prism to strike the photodiodes, which sense the signal level.
Often the problem is that the various lenses, prisms, beam splitters, and mirrors will become dirty (especially if in the house of a smoker) and thereby reduce the total light power striking the sensors. Only one lens is easily accessed, but cleaning this one often cures the problem. One can either clean that lens with a cleaning disc played in place of a CD. The spinning disc has soft brushes on the bottom that clean the lens. If this fails, one can unplug the unit from AC power, remove the cover, remove the bridge over the loading tray and clean the lens with a Q-Tip (cotton swab). Much more work, but much less expensive. Good luck!
Charles, many thanks and, yes, cleaning the collimator lens (the accessible part) can do the trick in some cases. I considered offering this advice. However my experience is that although this action may be fine with a soiled but otherwise good and serviceable OPU, with a 14 year old unit that has been used regularly any gain will inevitably be short lived.
The unit was purchased a few years ago from a person who used it only a few hours before putting it back in the original packing. So I purchased an almost new unit that I've used moderately heavily since I bought it.
That is encouraging. I had to assume that the unit was regularly in use since the model was introduced in 2003.
Of course those "few years ago" may be longer ago than you think ( time goes by so quickly) and I hope that the previous owner wasn't like a used car dealer where each vehicle was owned by a little old lady who only used it to drive to church on Sundays :-).
Anyway good luck with the cleaning. Just be careful how you do it. If you can, use a good pro photographer's lens cleaner fluid sparingly with pro lens cleaner tissues (careful use of a Q tip otherwise). if you can't get to the lens and have to insert a cleaning disc try to avoid the type with small sponges which you dampen with a fluid which are stuck to a CD . That type has the potential to knock the lens off its mounting. The other type (if still available) has a small spiral of carbon fibres. Less potential for damage but not great for removing oily deposits though OK for dust.
The manufacturuer of my own disc transport recommends the use of a "canned air" type of aerosol to deal with dust. That has the advantage of no physical contact and may not require opening up the machine.
Meanwhile I have no knowledge of any method for rejuvenating CDRs where the dye may be deteriorating, this being another possible element of your problem. They are just not suitable for the long term storage of data.
I'll give it a try. Thank you.
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