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KSS240A lens vibrating

Discussion in 'Electronic Repair' started by [email protected], Oct 25, 2005.

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  1. Guest

    Hi,

    never come across this so thought i'd post and see what people think.

    I just got hold of a Sony MHC1600 cd/radio unit. When in cd mode there
    is a noise coming from within the unit. I took then unit apart and the
    noise is the cd lens assembly vibrating. If you put your finger on the
    lens and press (this has probably knackered it anyway) then you can
    stop the vibration and noise.

    Is the optical assembly the culprit or could it be something else . I
    can get hold of another optical assembly easily enough which i'll do
    anyway but anyone seen this before?

    Kind Regards

    Steve
     
  2. Probably the pickup itself, but you just have to replace it to find out for
    sure.

    Welcome to the exciting world of electronic repair.


    Mark Z.
     
  3. Tim Schwartz

    Tim Schwartz Guest

    Hello,

    Sony had a problem with the KSS-240A optical pick ups having an
    oscillation problem, usually 800 Hz, and it can be so loud that it
    causes the unit to start skipping. Sony had a cure of adding a brass
    weight to the optical pick up, and a felt washer to the clamper. I'm not
    sure it this applies to all application of the KSS-240A or not.

    From a Sony Technical News bulletin that I've got a faxed copy of, the
    weight is part number 4-962-979-01, and the screw to attach it is
    7-685-134-19. The screw replaces the one holding the PC board with the
    pots to the laser. The felt washer is 4-986-769-01, and goes on the
    surface of the clamper that touches the disc.

    The machines that show this do not do it on all discs, and it seems to
    be the worse 5-12 minutes into the disc. Please be aware that original
    Sony KSS-240A lasers have 3 pots on the PC board, a cable connector with
    a clamp, and that the chip on the bottom is 14 (or is it 16) pins.
    There are many 'after market' lasers sold as KSS-240A that have a single
    pot, no clamp on the cable connector and an 8 pin chip.

    Regards,
    Tim Schwartz
    Bristol Electronics
     
  4. I forgot about that one! The vibration from the spindle motor sets up a
    resonance in the pickup. You can see it in the focus error and tracking
    error waveforms. Lowering the tracking or focus gain a bit can help also,
    and adding some silicon sealer or RTV where the spindle motor contacts the
    BD board.

    Mark Z.
     
  5. Tim Schwartz

    Tim Schwartz Guest

    Hello all,

    I got a reply from the original poster that this conditions happens
    when CD is selected on the unit, even with NO DISC in the player, so it
    is certainly NOT the vibration I was thinking of, and the weights will
    not cure it.

    If the lens is going onto oscillations with no disc, I'm inclined to
    believe there is more likely to be a problem in the control circuit than
    with the optical block itself. I'd look for power supply problems too.

    Regards,
    Tim Schwartz
    Bristol Electronics
     
  6. Ron(UK)

    Ron(UK) Guest

    I`d scope the supply lines looking for ripple from a dodgy cap in the psu.

    Ron(UK)
     
  7. Guest

     
  8. Guest

    Hi all,

    Many thanks for the replys, very interesting.

    I've done a bit more investigation now I have the schematics. I can't
    see anything obvious like blown caps or anything. However the chip the
    circuit uses for driving the sled motor, drive spindle and
    (importantly) the focus/tracking coils (which I think is causing the
    oscillation) is an LA6525 surface mount IC. When the power is applied
    and the optical head vibrates, this IC gets very hot, very quickly.
    According to the datasheet for this iC it does have thermal protection.
    Anyway if I disconnect the optical assembly ribbon cable, the chip does
    not get hot.

    I have ordered a KSS-240A so I can try it when it arrives. Does anyone
    think it's worth getting hold of the chip as well (assuming I can)

    Cheers

    Steve
     
  9. Guest

    Hi all,

    Many thanks for the replys, very interesting.

    I've done a bit more investigation now I have the schematics. I can't
    see anything obvious like blown caps or anything. However the chip the
    circuit uses for driving the sled motor, drive spindle and
    (importantly) the focus/tracking coils (which I think is causing the
    oscillation) is an LA6525 surface mount IC. When the power is applied
    and the optical head vibrates, this IC gets very hot, very quickly.
    According to the datasheet for this iC it does have thermal protection.
    Anyway if I disconnect the optical assembly ribbon cable, the chip does
    not get hot.

    I have ordered a KSS-240A so I can try it when it arrives. Does anyone
    think it's worth getting hold of the chip as well (assuming I can)

    Cheers

    Steve
     
  10. nathanjh13

    nathanjh13

    3
    0
    Jul 6, 2010
    I may be having a similar problem to this but i'm a little out of my depth to diagnose. I'll record the problem and upload. Nice to meet you all in the meantime

    Nathan :)
     
  11. nathanjh13

    nathanjh13

    3
    0
    Jul 6, 2010
    Hiya, I'm out of my depth but think this may be a similar problem for me...

    I've uploaded a diagnostic clip onto youtube here:



    If anyone is at a loose end and might be able to shed some light on this i'd really appreciate it.

    Nathan :)

    There's a full description when the text box under the video is expanded.
     
    Last edited: Jul 6, 2010
  12. nathanjh13

    nathanjh13

    3
    0
    Jul 6, 2010
    Yeah, this is a KSS213A component and suffers similar problems to the KSS240A I've learned. Will replace and see how it goes. Made assumption i can replace like for like but I'll see. Thanks
     
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