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Philips MC-110 micro midi style stereo.

Discussion in 'Electronic Repair' started by ian field, Jul 17, 2007.

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  1. ian field

    ian field Guest

    TBH I'm not keen on working on audio stuff - especially ones that have
    mechanical bits and servos and stuff, so I may even weigh up the cost of
    someone else having a look against the price of a new one.

    The CD plays normally for about an hour then the spindle motor gradually
    becomes erratic, slowing, stopping and occasionally going backwards, I've
    only had it about 4 years, which seems a bit soon to bin it so I wondered if
    its a stock fault anyone can tell me where to look for?

    TIA.
     
  2. N Cook

    N Cook Guest

    Prop it up at an angle for a few hours and see if the malfunction occurs
    much earlier or not at all then probably mechanical/ connection problem than
    electronic control problem. If mechanical then break/remake all connections
    would be a good start.
     
  3. ian field

    ian field Guest

    When it first packed up I replaced it with a seriously cheap & nasty deck,
    so I carried on using the Philips speakers and put the old deck in the box
    with the tacky plastic speakers, recently I borrowed the tacky speakers and
    while I had the box open had another play with the Philips deck. Short of
    space to set it up in, it was on an uneven surface anyway and I patted it
    about a bit to see if there were any glaringly conspicuous dry joints/loose
    connections, its hard to tell with erratic behaviour but patting it about
    didn't make a noticeable difference.
     
  4. Arfa Daily

    Arfa Daily Guest

    Hi Ian, how's it going ? Did you know that Steve is hoping to get T @ H
    going again soon as a web based publication? Different name again though ...

    Is that one of the Philips units that has the three-player mech with the
    trays that slide over one another ? If so, it's quite likely that the laser
    is either dusty or worn. Be warned though that this is not an easy mech to
    dismantle to get at the laser. There are timing issues if you accidentally
    get it screwed up, which is easy enough to do, even without dismantling it.
    Unless you have the instructions, or have done a lot of them, you would
    never figure it out by trial and error ... Just as a matter of interest, the
    electronics and spindle motors on these are generally pretty reliable.

    Arfa
     
  5. ian field

    ian field Guest

    Its a single CD player with synth tuned AM/FM and cassette, the CD deck is
    on top and the "lid" flips up like the lid on a wheely bin, there's no CD
    transport system or drawer - the CD is simply put on the exposed hub.

    When the spindle turns correctly it plays ok although I did try one of those
    laser cleaning disks with the little brushes on and a bottle of iso-propyl.
     
  6. Arfa Daily

    Arfa Daily Guest

    Ah, OK. I know which one it is now. It's worth just giving the lens a
    'proper' clean with IPA and a cotton bud. I've never been much enamoured
    with the bristled cleaning discs. At best they don't do a very good job, and
    at worst, I've seen the bristles get caught in a laser's superstructure, and
    do damage to the lens carrier ...

    Beyond that, the most likely problem is the laser itself. Stopping reading
    after some period of operation, is a fairly common failure mode.

    Arfa
     
  7. ian field

    ian field Guest

    Would a faulty laser cause the spindle motor to become erratic?

    The disk reads OK until the spindle motor starts playing up.
     
  8. I fixed a "Hifi separates" CD player with identical symptoms a few
    years ago. It had a pair of transistors (one NPN one PNP, to + and - rails)
    driving the spindle motor, and one was leaky (getting worse when hot).

    It's the only CD player I've ever seen where the spindle motor
    run the wrong way at any time.

    Mike.
     
  9. Arfa Daily

    Arfa Daily Guest

    It is very common for the motor to run backwards on any make and model, when
    the spindle servo loses lock. The spindle motor running 'erratically' is
    more likely to be a symptom, rather than the cause. Control of the spindle
    servo is as a direct result of correctly decoding the servo control info in
    the recovered data stream. If the data stream starts to become corrupt to
    the point where the software and hardware error correction systems can no
    longer derive valid control data, the servo will lose lock, and the
    rotational speed will become erratic. This further exacerbates the
    situation, until the whole servo loop goes unstable, which is when the disc
    is likely to either start spinning backwards, or comes to a stop with
    twitches or pulses of brief rotation. The commonest cause for the data
    becoming corrupt, is a defective laser. That's not to say that a similar
    problem *can't* be caused by a defective motor, or the external control
    circuitry, which these days is either contained all in one chip, or in a
    servo processor chip plus a motor driver chip.

    Usually, problems with the motor itself, are confined to DVD players, where
    they are worked much harder with the higher rotational speed involved, so
    tend to have a shorter lifespan. I have had faulty motors on CD players -
    notably the Pioneers from a few years back, and some Panasonics - but on
    other makes and models, they are fairly rare, compared to bad lasers.
    Usually, if you have a motor problem, it will start to show on later tracks
    on a long disc. This is because CD players use constant angular velocity,
    which means that the disc rotates slower as the laser moves towards the
    outside of the disc. Any brushgear wear leading to poor motor performance,
    shows up worse at lower rotational speeds. You can get an idea if this is
    the problem, by playing a couple of tracks at the start of a long disc, to
    warm up the motor, then forward skipping straight away to a late track near
    the end. A dicky motor will usually show up at that point. If it doesn't
    immediately start giving trouble, you might also find that it has become
    very 'tap sensitive' at this point, as the data is getting close to being
    compromised by poor rotational stability.

    Poor motors also often show a marked increase in commutation noise, measured
    with a 'scope directly across the motor terminals. If you can find either a
    testpoint or an IC pin marked "RF", you can perform a more 'technical'
    diagnosis by observing the eye pattern on this point. Well defined and
    stable 'diamonds' in the pattern indicate stable rotational speed.
    Twittering of, or the diamonds looking out of focus, particularly on later
    tracks, can indicate a poor motor. The size of the RF waveform is a good
    indicator of laser condition. On most players, if there is a testpoint, the
    expected level on it is about 0.8 to 1.2v p-p. If the level drops off over
    playing time, this normally indicates a worn laser.

    Hope that clears up a few points, and helps with getting to the bottom of
    it.

    Arfa
     
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