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JVC XL-PM25 doesn't recognize mp3 CDs

Discussion in 'Electronic Repair' started by Harald Kleiner, Sep 4, 2005.

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  1. short form:

    This portable CD player doesn't recognize data- (mp3-) discs. It does
    play audio discs so I don't know why it has trouble with data discs

    long form:

    This portable CD player seems to have received a hard shock like falling
    to the floor. When I put it out of the, well, scrap box, one hinge was
    broken and it didn't recognize any CDs.

    Following the steps in ("startup problems") I found out
    that focus was established ok but there was a tracking problem.
    After taking off the shielding from the pickup i noticed that the
    hair-thick wire from the tracking coil was broken. Fortunately I could
    establish a drop of solder joining the two ends of wire again.

    Now the device plays CDDA-discs quite well but only if I turn off ASP
    (anti shock protection):
    When ASP is on the disc spins up to double speed and music is played in
    double speed (just as in fast forward seeking mode). A bargraph is drawn
    on the display that starts getting "full". When "full" level is
    achieved, disc slows down to 1x but it doesn't play out of the buffer
    (slowing down the disc "manually" immediately has effect in autio
    output) and sound is "scratchy". This seems rather weird because other
    functions do work quite normal...

    When I insert a mp3 disc startup sequence is as follows:
    * establish focus (lens moves up, down, up again and starts to wobble
    with the disc)
    * spin up
    * move head out of the innermost position (maybe searching for TOC?)
    with some very short breaks in between
    * move back to start
    * re-establish focus once again
    * do the same move-steppy-out-of-center
    * disk keeps on spinning, head isn't moved any more; display still says
    "Reading compact disc" and nothing more happens.

    Watching the eye-pattern gives no clue. It looks pretty normal and
    especially it looks the same for cdda and mp3-discs.

    question section:

    * is there anything I could check or adjust? There is just one
    potentiometer located on the pickup (don't know what it is for so I
    didn't touch it up to now)

    * what do you think about the ASP-problem? Why is just ASP faulty (I
    mean ASP ist just one of tousands of features in the chipset, if the
    chip was dead nothing would work).

    * Could be there a connection with not reading data discs? (i wonder...)

    thank you very much for any comments and tips!

    kind regards,
    Harald Kleiner
  2. Jeroni Paul

    Jeroni Paul Guest


    It seems likely that you've got some broken trace in the board,
    specially around the microcontroller area. The ASP problem is likely
    because the CDDA decoder chip isn't configured adequately to take data
    from memory instead of laser reader.

    Broken traces can be hard to see, just check with your multimeter all
    traces near the board edges.
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