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Sony laser questions

Discussion in 'Electronic Repair' started by [email protected], Mar 21, 2007.

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  1. Guest

    I received a Sega CD (old model with the motorized tray), and had some
    questions..

    When I first got it, putting in a CD resulted in the sound of the
    motor spinning up, stopping, spinning up, stopping, then the Sega CD
    reported NO DISC.. So, I took the unit apart, and was stunned to see
    what I saw the thing do.. When it first spun it up, it stopped, then
    the disc spun in reverse, then gave up with the NO DISC message.

    The laser in the unit was a Sony KSS-240A.. I then proceded to turn
    the three POTs, one at a time, VERY slowly, like 1-2 degrees (maybe
    3), and if it didn't help, I went the other way, and if that didn't
    work, i'd return it as closely as I remembered it's position, then go
    to the other POT...

    Well, after all three POTs, non of them helped, still had the weird
    erratic actions... Then, I remember someone telling me the 240A has
    TWO lenses, one on the top, and one on the bottom.. So, I took the
    plastic piece off, carefully lifted up the lens, and blew into it..

    After that, the machine has been reading games, and music CDs... But,
    at one point in a certain game, when it played a certain CD audio
    track, it did the weird "spin up, spin down" thing, and decided to
    freeze the whole game up.. I try again, at the SAME audio track it
    did the same thing.. So I cleaned the CD, and then it worked
    perfectly..

    My question: Could messing with the POTs made it more sensitive to
    smudges on a CD? Or are the 240A's just weak lazers? My Sony boombox
    has the same KSS laser, and it used to do the SAME thing, until I took
    compressed air at it's lens..

    Also, though I did put the POTs back in their original position, I
    fear 1, 2, or all 3, may be 1-3 degrees off from their original
    position.. Can this hurt the system?
     
  2. Arfa Daily

    Arfa Daily Guest

    KSS240A lasers are for sure not the most reliable in the world. The pots on
    there are factory set and sealed, and should not be adjusted. With most Sony
    lasers, even a modest over-drive of the laser diode can do it permanent
    damage, so I would not recommend anyone to attempt adjustment, unless it is
    a last ditch "do or die" attempt to prove that the laser is worn out. The
    dust that you are blowing by going down the side of the lens, is likely
    laying on the critical-angle mirror that's down there, and if that is the
    case, there is probably a similar amount of dust on the pickup diode array,
    which likely won't be dislodged by air-blowing. This dust will also degrade
    the performance of the laser, and I would think that when a small amount
    builds up on the mirror as well, that is enough to tip the performance over
    the edge, and stop it working.

    Blowing the dust off the mirror, just about gets the performance back up
    for a couple of months to the point where the external circuitry can handle
    the reduced level signal output that the dust is causing. Sensitivity to
    marks on the disc, and failure to play with the disc spinning backwards, are
    both typical symptoms of a worn or faulty laser.

    Personally, I would just go ahead and replace it. Although not one of the
    cheapest of the Sony KSS series lasers, it never-the-less is not
    prohibitively expensive either. The only thing that I would warn against, is
    using a generic 240A substitute, such as an NKS240A. Although most cheap
    subs for the KSS series work just fine, I have found that in many
    applications using the '240, only a genuine Sony original will display the
    performance required for reliable operation.

    Arfa
     
  3. Guest

    Ok, thanks for the information..

    Since I did mess with the POTs, and they are probably 1-3 degrees off
    a little, will this cause major problems in the long run? Right now
    it seems to work at the moment, as long as the CD is spotless...
     
  4. Arfa Daily

    Arfa Daily Guest

    As long as it is working at the moment, it is unlikely that you have done
    any long term damage. Although the settings of the pots are quite critical
    ( two of them are in the tracking and focus servos, and one is the laser
    power pot as I recall ) a few degrees from their original set positions,
    should not be anything to worry about

    Arfa
     
  5. Guest

    Good, so I can put my mind at ease... lol

    I forgot to mention in the original post of mine, the first CD I
    tried, the one that spun backwards, was a printed music CD (real
    CD).. And the game CD that froze at a certain audio track was a CD-
    R..

    being the CD-R game was super sensitive, im wanting to give it the
    benefit of the doubt it was because it was a CD-R, though I used a
    special type of "mastering" CD-R, ones the music industry use, and
    would think the KSS240a would atleast have no problem with those...
     
  6. Arfa Daily

    Arfa Daily Guest

    A burnt CD is nothing like as reflective as a pressed CD, so any laser
    low-output issues, will be exacerbated with a home burn over a commercial
    pressing. Actually, '240s are particularly bad for not liking anything other
    than genuine pressed discs, and need to be in really good condition to play
    them successfully

    Arfa
     
  7. Guest

    Ok. What compatible replacement laser assmebly do you reccomend?
    Being it's in a tray loading Sega CD, does it have to be an EXACT
    match? (will the Sega CD even know if the drive is changed?) Also,
    what replacement will accept a CD-R, the best?
     
  8. Arfa Daily

    Arfa Daily Guest

    It has to be replaced with a KSS240A, and I would recommend a genuine Sony
    one, if you can find a supplier. Do not use one of the subs such as the
    NKS240A. I have never had much luck with them. If you find a website selling
    lasers, you will often find two prices quoted. The cheaper one is usually
    for a second-source replacement, and the slightly more expensive price is
    for a genuine Sony original, which may be actually declared as such. I would
    recommend going for the Sony original in the case of a KSS240, as they are
    fussy lasers at the best of times. For products which use the KSS213B or
    KSS213C, cheap second source replacements are usually fine. For KSS213D, E,
    or F, again I tend to use genuine originals. If your unit is going to be
    working a lot with home-burn discs, I would definitely go for a genuine Sony
    replacement. No alignment should be necessary after replacement. As you say,
    it shouldn't even 'know' that the laser has been replaced. There is not even
    a shorting blob to remove on a '240. You can just drop the new one right in.
    I would however recommend that you wear a wrist strap connected to an anti
    static mat to do the job on, as laser diodes are quite sensitive to static
    discharge, when their connections are open, as they are on the '240 until
    it's plugged in.

    Arfa
     
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