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Lite-On SHM-165P6S04C, sticking tray problem - fix

Discussion in 'Electronic Repair' started by David Mathog, Sep 24, 2007.

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  1. David Mathog

    David Mathog Guest

    I'm posting this with hopefully enough keywords so that other people
    can Google and find it, and so save themselves some time if they run
    into the same issue.

    We have 8 identical workstations, each with a Lite-On SHM-165PS
    CD/DVD optical drive. One of these drives had the following symptoms:

    1. At BIOS (or in linux, or in Windows), pressing the front panel eject
    button would result in a couple of "clunks", and the tray might move
    a millimeter out, but the tray would not open.

    2. If the front panel button was pushed enough times, or linux "eject"
    was used, it might open eventually. If it did then pressing the button
    again and again eventually resulted in it working every time. Except
    that giving it even 10 seconds rest would put it back to the beginning.

    3. With no power, pushing a paper clip in the release hole would
    release the tray.

    4. The motor could be heard whirring when it was active.

    5. With front bezel and tray cover removed (and being careful to look
    at an angle, so that no reflected laser light would go directly into
    my eyes) I observed that during the clunking the emergency release was
    retracting, and then eventually returning to its original position just
    before the drive gave up.

    The drive was removed from the machine and the top and bottom
    of the case also removed. The rubber band was intact and seemed
    tight enough. Even so, I tried replacing it with an O ring of
    the same size, as this solves CD/DVD tray problems 90% of the time.
    Unfortunately, it wasn't the solution this time.

    To understand the repair one must visualize the tray mechanism, so
    please bear with me.

    Picture the drive in the normal upright orientation on the table
    in front of you, with the tray opening towards your chest. There
    is a "locking rack" which runs left to right across the top/front
    of the drive just below the tray. It is easiest to see it
    with the tray removed. The left hand side of this rack contains the
    "paper clip" tray release mechanism. This consists of about an inch of
    linear gear teeth on the rack mated to 1/4 of a circle of teeth on the
    release lever/gear. On the right hand side of the rack there is a
    shorter run of similar teeth which (can) mesh with a gear driven through
    the rubber band by the motor. This driven gear meshes both with the
    teeth on the rack and with the teeth on the bottom of the tray.
    Slightly to the right of these rack teeth there is a small plastic
    pin which sticks up vertically out of the rack. This pin fits into
    a groove on the bottom of the tray, on the right side from the
    specified viewing position. There is an outlet in this groove which
    allows the pin to leave the groove when the tray is (nearly) closed.

    Now then, when the tray is closed the rack is driven by the motor all
    the way to the left. The pin is out of the groove. Before the tray
    opens the rack moves to the right, driven by the gear. This also
    retracts the paper clip emergency release lever. The pin moves with the
    rack, engages into the tray slot lead in, by hitting a wall of that at a
    45 degree angle, and this pushes the tray out slightly so that the tray
    teeth will engage the gear as well. As the tray moves the pin in the
    tray groove pulls the rack slightly farther to the right, which
    disengages the rack teeth from the drive gear. The drive gear
    stays engaged with the teeth on the bottom of the tray to
    open the tray.

    Careful inspection showed a series of very fine scratches on the tray
    groove where this pin engages/disengages. Figuring that scratches
    indicated something other than a smooth motion, a small amount
    of white grease (from elsewhere in the mechanism) was applied to the top
    and sides of the rack pin, and also to the 45 degree section of the lead
    in groove on the underside of the tray. This tiny amount of lubrication
    was all that was required to fix this problem.

    Note that there is no evidence of grease on the lead in groove of the
    trays on any of the other drives. So I suspect the design intended that
    the interaction between the pin and the lead in groove 45 degree wall
    not require lubrication. However, apparently sometimes it does. The
    45 degree wall in the lead in groove on the bottom of the tray
    can be (lightly!) greased without disassembling the drive if the tray is
    first opened with a paper clip.

    Regards,

    David Mathog
     
  2. Meat Plow

    Meat Plow Guest

    Snipped for brevity.

    I just repaired a Lite On drive that had identical
    problems. Turned out to the be mechanism belt. I simple cleaning was all
    that was needed. The belt is up front and exposed to a constant inward
    airflow which undoubtedly subjected it to volumes of air-born
    contaminants. This drive however would operate normal if media was inside.
    You didn't mention this.
     
  3. David Mathog

    David Mathog Guest

    That was my first thought but changing to a new O ring didn't fix it.

    The drive here didn't open reliably, whether or not there was a disk in
    the tray.

    It's on open question as to why this one drive needed that point
    lubricated, but seven other drives didn't.

    Regards,

    David Mathog
     
  4. Meat Plow

    Meat Plow Guest

    Mine would not open at all unless it was loaded then it worked every time
    :)
    Yep that is odd.
     
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