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MFM Miniscribe HDD does not spin, how to repair??

Discussion in 'PC Hardware' started by XYLOPHONE, Dec 2, 2011.



    I am trying to get my 20MB Miniscribe 3.5" hard drive running again.
    The problem is that it doesn't spin up anymore when I power it up. I
    disassembled the drive's PCB, and swapped it with the PCB from a
    working drive, and the other HD works with both PCBs, so proving the
    problem is with the spindle motor itself.
    Looking closer at it, I notice that when I power it up, the platter
    spins about 1/4 of a revolution, then stops forever, until I power off
    and on again. Rotating it manually doesn't fix it.

    What could be the problem? I feel that if I can get the HDD to
    correctly spin again, I should be able to access the data. This drive
    is vintage, so I'm doing all efforts to rescue it.

    Thanks for any information, any hint, or any similar situation

    XYLOPHONE, Dec 2, 2011
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  2. "Vintage"!? Wasn't it on one of those drives that Noah kept track of all
    the animals? :)

    Have you tried giving the drive a sharp twist about the axis of the spindle?

    Percival P. Cassidy, Dec 2, 2011
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    Krypsis Guest

    That should work! Sounds like the OP has what is termed a "stiction
    fault". This is caused by the heads being stuck to the platter. The
    sharp twist, often with power applied, is enough to break the "stiction"
    and allow the heads to float free. Note that, if power is applied when
    doing it, there is a risk of damage so treat the device with kids gloves
    if you need to do it this way.

    Haven't seen this fault in many a long year. No doubt this is due to off
    platter head parking mechanisms on all drives nowadays.
    Krypsis, Dec 2, 2011

    Arno Guest

    First, if the data has any real worth, STOP MESSING AROUND and
    get help from a professional data recovery service. Chances are you
    will just make matters worse.

    As you say the drive spins 1/4 revolution, so it cannot be stiction.

    Sounds like not all coils in the spindle motor get powered. As
    you tried the PCB swap, this would not be a problem with the motor
    driver amplifiers. One possibility is a contact problem.
    Another one is a possibly broken winding in the motor itself.
    Both can be debugged with a multi-tester by mesuring winding
    resistances. (If you have no clue what I am talking about, then
    you are not qualified to look into this, sorry.)

    The contact problem is typically easy to fix temporarily
    when located. The broken winding is usually unfixable.

    Arno, Dec 3, 2011


    Thanks Arno, I'll carefully try to see the contacts.

    However, I forgot to mention that, when I first removed the PCB,
    everything underneath was covered with tiny DARK BLACK dust, just like
    black laser printer toner, or maybe even smaller grain powder. I
    gently wiped all that black dust away. When I removed the PCB from the
    working HDD, there was a little bit of that black dust, but far less
    than on the non-spinning drive.

    Does this dust make a click to anyone?

    Thanks again...
    XYLOPHONE, Dec 3, 2011

    Jerry Peters Guest

    Disintegrated foam perhaps? I seem to remember dismantling a drive
    with a thin piece of foam between the pc board and the drive. Might
    have been to dampen vibration.

    Jerry Peters, Dec 3, 2011

    Franc Zabkar Guest

    Is there a sintered carbon brush that bleeds the static electricity
    off the motor shaft?

    - Franc Zabkar
    Franc Zabkar, Dec 3, 2011

    Rod Speed Guest

    Jerry Peters wrote
    I've never seen any foam deteriorate as comprehensively as that.
    Yes, some Seagates did have that at one time.
    Dont believe it was for that.
    Rod Speed, Dec 4, 2011

    GMAN Guest

    I remember those from my Atari ST years. You occasionally would get them
    making god awefull sounds when they would wear down and some would suggest
    anything from sewing machine oil(3 in 1 oil), to using a dab of facial grease
    (Shrugs head???) to stop the squealing.
    GMAN, Dec 4, 2011
  10. Does the RedHill.net.au have any info? HDDguru.com forums are
    dominated by people who do HD repair and data recovery.

    I would try unplugging the cables from that motor and the motor of a
    working drive and compare the resistance readings of their coils.
    However resistance measurements don't always tell everything about
    coils, and for that you need to ring the coil:



    Is it possible to replace the motor without opening the drive? I have
    a feeling dust would be a problem if even if the motor can be removed
    that way.
    larry moe 'n curly, Dec 5, 2011

    Arno Guest

    I think in this particular case, resistancw will be enough, as
    a HDD motor has at least 3 identical coils. However if the
    resistance is very low, measuring it could be tricky.

    For reference: On a 12 year old Fujitsu 3.5" drive I still
    have, the windings come in at 3 Ohm. That is within the usable
    range of a nomal multitester, if some inaccuracy is
    not an issue.

    Arno, Dec 5, 2011

    Rod Speed Guest

    larry moe 'n curly wrote
    Its academic because it cant be.
    Rod Speed, Dec 6, 2011

    Franc Zabkar Guest

    I still don't see any resistance measurements. Do you know how to use
    a multimeter?

    Does your drive have a tach sensor? Often there will be a Hall effect
    sensor that provides RPM feedback to the controller. Modern drives
    sense the back EMF in the non-driven winding, but earlier drives used
    discrete sensors.

    If you don't understand what to look for, then upload some photos to a
    file sharing site so that someone can assist you.

    - Franc Zabkar
    Franc Zabkar, Dec 8, 2011
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