Author Topic: The Curse of the Old Music CD Player: Optics or Motors?  (Read 17573 times)

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Offline sonicj

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #25 on: November 07, 2010, 05:37:25 am »
i recently repaired the superdrive in my macbook pro. it started to have problems initially only when writing to the disc. eventually it would neither read nor write to dvd nor cd. disassembled 1/2 of the computer, opened up the drive, cleaned the lens with zeiss wipes and a loupe (normally would have used a denatured alcohol that doesn't leave residue or everclear, but thats all i had at the moment), further disassembled the unit to gain access to the rails, cleaned old lube off with kimwipes & cotton swabs, relubed rails with triflow synthetic grease and a toothpick, reassembled. everything works as new!

cleaning laser lens? you just want to make it worst! and i've put my eyes right directly to the laser, and i can say the warning is both "bullshit" and "not bullshit"
this is very, very bad idea! just because the radiation emitted is not within the visible light spectrum or does not cause immediate pain or discomfort does not mean it is safe to look at.
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Offline Mechatrommer

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #26 on: November 07, 2010, 07:30:15 am »
...cleaned the lens with zeiss wipes and a loupe (normally would have used a denatured alcohol that doesn't leave residue or everclear, but thats all i had at the moment), further disassembled the unit to gain access to the rails, cleaned old lube off with kimwipes & cotton swabs, relubed rails with triflow synthetic grease and a toothpick, reassembled. everything works as new!
i guess you worked in "sahara". i never had dust issue. use a blower is the safest bet. usually a lil bit of small dusts wont affect the performance, i guess the others suggestion about the laser diode is the most affecting part of the operation.

i said it both bull and not coz a quick look wont damage your eye, but overdoing it could. the light is irritating tough. just did it once, just to try... and to tell the world. i'm still ok here with both eyes working ;) and IIRC there is no discomfort or headache afterward, but for the young player, my suggestion is to just follow the warning. there are other more brilliant method to test the laser.
« Last Edit: November 07, 2010, 07:32:12 am by shafri »
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline sonicj

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #27 on: November 08, 2010, 12:31:45 pm »
i guess you worked in "sahara". i never had dust issue. use a blower is the safest bet. usually a lil bit of small dusts wont affect the performance, i guess the others suggestion about the laser diode is the most affecting part of the operation.
this form of failure is common for apple slot-load drives.
 

Offline .o:0|O|0:o.Topic starter

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #28 on: November 09, 2010, 04:28:52 pm »
These laser modules are incredibly fragile, and very easy to damage irreversibly. However, in comparison to the cheaper modules, those found in CD-ROM players are built like tanks (see pics).

I pretty much determined right from the start that it wasn't a dust issue from the behaviour of the system -- and apparently, from one of the repair faqs posted (thanks for that), the light emitted isn't affected that much by the amounts of dust that might enter the unit over time. In fact, it is interesting to note that the laser diode isn't actually situated directly under the collimating lens but hidden away under to a side at at 90 degree angle, so that the beam is reflected off an inclined reflective strip through the lens. The lens is raised and lowered using a delicate solenoid based mechanism.

The problem I had was that the diode had failed. I don't know what the rating was for this particular diode, but they seem to be rated at far lower than your typical LED, at around 7 mA, perhaps someone can correct me if I am wrong. I didn't want to risk damaging the good laser by adjusting the trimmer which I imagine is there to limit current, so I "simply" (it wasn't) transplanted the better diode into the circuit ...and it works!

I don't know if anyone else has noticed this, but some CD players use light on the red spectrum and others use blue. Since CDs are made to a certain specification I would imagine that both are equally effective, but that perhaps the photodiode might have to be matched according to the wave~length. However, blue photon's are more energertic than red ones so I was wondering if there would be any advantages to using blue over red....

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« Last Edit: November 09, 2010, 04:32:16 pm by .o:0|O|0:o. »
 

Offline Mechatrommer

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #29 on: November 09, 2010, 05:23:17 pm »
I didn't want to risk damaging the good laser by adjusting the trimmer which I imagine is there to limit current, so I "simply" (it wasn't) transplanted the better diode into the circuit ...and it works!
initially its already been damaged while u open it, so what do u got to lose by adjusting the trimmer? and u got the hassle of dissambling the diode unit.
good info though, now i know, replacing diode could fix it... how do you know which diode replacement is good/compatible for the unit? i have many cd/dvd player/rom here, each unit got different laser unit, how to see the diode spec?
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline .o:0|O|0:o.Topic starter

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #30 on: November 09, 2010, 07:32:07 pm »
Shafri:
By tampering with the trimmer with the faulty diode still inserted I wouldn't have learned much more if anything and it would have added further uncertainty if, after inserting the functioning diode, it didn't work.

Unless there is a part number and associated data sheet, the only way of knowing for sure that you have a suitable replacement (assuming the two diodes are uknown to you) is through measurement. The problem with measuring forward current and associated output is that you may damage the device.

...The metal casing of the CDROM module acts as a heatsink for the diode. The plastic module from the crappy stereo system does not serve that purpose and as a result you have a dead diode after far less use. Unfortunately I couldn't swap the entire module, so I will probably end up with another dead diode eventually.

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Offline Mechatrommer

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #31 on: November 09, 2010, 11:37:25 pm »
i mean how do you get a diode from another model to be working on another model? are they the same part number? (the diode)?
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline sonicj

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #32 on: November 10, 2010, 04:31:04 am »
i mean how do you get a diode from another model to be working on another model? are they the same part number? (the diode)?

screwdriver, spudger, dremel, loupe, skill, luck, epoxy

sometimes a electronic device has to die in order for others to live on. common computer drives are rarely "worth" the repair effort. regardless of the outcome, taking them apart to learn to how they work gives you the knowledge, skills and confidence to take on repair challenges of more valuable devices.
-sj
 

Offline .o:0|O|0:o.Topic starter

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #33 on: November 10, 2010, 10:14:48 am »
"Sometimes a electronic device has to die in order for others to live on."  :D

I have destroyed CDROMs and CD players before so I had the feeling it would be possible to effect an easy switch between the two parts. Luckily there was no epoxy involved and I was able to ease the diode out with a small screwdriver. The diodes were of similar dimensions, which made it all a lot simpler. The hardest part was desoldering and resoldering the pins from the flexi and then reassembling the stereo.

The stereo was built so poorly inside that it is probably not a design to go by, but I noticed that instead of using an integrated full-wave/ bridge rectifier, they used a small board with discrete components: 4 diodes, 1 electrolytic and 4 ceramics. I have seen these modules before, but I would have thought it would be cheaper to use an integrated rectifier. Furthermore, they used 4 ceramics at that stage, considering the cheap construction (I have a Philips amp that uses something similar, but only requires 1 ceramic between Vout and ground). It looked like they bought a bunch of different modules from different places, wired them together and jammed everything into a deceptively charming little enclosure. Not designed to last, which is a shame because most individual components tend to have a good ten years in them if used properly. I wonder how many components they used unnecessarily.

I guess the reason people don't return the products 4 times within a year is because they last long enough for people to discard the proof of purchase and are so cheap in the first place that it is hardly worth the hassle six months to a year down the line. I once bought a pair of Chinese in-the-ear type ear phones for a few pounds. I didn't expect the sound to be great, but I was a bit surprised when picking them up a few months later the foam/sponge which had gone hard crumbled between my fingers.

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Offline Time

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Re: The Curse of the Old Music CD Player: Optics or Motors?
« Reply #34 on: November 10, 2010, 05:23:09 pm »
A smaller wavelength will let you resolve smaller images.  This is due to optical effects like diffraction which impact focusing spot size.  So naturally a blue laser can read much more tightly packed data off a disc which in the end allows for more information per disc.  Photon energy is proportional to wavelength so I guess it isn't incorrect to say its the energy that gives you a better resolution.  Its more accurate to say wavelength.

Do not stare into laser diodes.  Especially the ones from optical drives.  Those warnings are not bullshit and if you think so keep staring into them and report back.

-Time
 


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