Disk not spinning up

Valeri Galtsev galtsev at kicp.uchicago.edu
Sun Sep 17 23:09:33 UTC 2017

On Sun, September 17, 2017 4:02 pm, Ralf Mardorf via freebsd-questions wrote:
> On Sun, 17 Sep 2017 22:50:42 +0200, Polytropon wrote:
>>> The best approach is to per-warn up the drive hardware before trying
>>> to power it on. Put a bear light bulb or shine a flood light from a
>>> close distance on to the metal covered side, IE; not the circuit
>>> board side, until it gets almost to hot to touch. Then power it on
>>> and and away you go almost every time this happens.
>>I will definitely add this as even more help.
> Usually it's worn out hardware from too many spin downs and spin ups. I
> doubt that aged lubricants are the cause.

I agree. Ages back harddrive manufacturers started using "lubricant free"
bearings. Often lubricant is a composite part of exterior of the bearing.
In  precision equipment even if liquid lubricant is used it is such that
does not change viscosity. If is is capable of gradually evaporating, it
is evaporating as a whole, without leaving residue, and without changing
its properties when partially evaporated. E.g. old mechanical watch makers
used "bone oil". When drive spins, as the center of mass is slightly off
the axis, shaft presses in all directions. Uneven wear even with very
uniform bushing material, is promoted if hard drive is positioned
vertically (i.e. axis is horizontal). That is why I did my best to avoid
hardware with hard drives positioned vertically. Wort mode of wear is when
bushing becomes elliptical. You can hear rattling noise (excessive
vibration) sometimes when that drive spins. As minimum energy of spinning
body is when its center of mass is on axis of rotation, there is chance
that platters will maintain nice rotation once they are brought into that
state. That is why knocking on one side (in direction ortogonal, or
slightly diagonal sometimes helps to spin it up).

Another likely thing is small particle caught where there is narrow gap
between stator electric magnets and magnetic surface of rotor. Often these
dirt particles are ferromagnetic, so the will never leave that area on
their own. As you, Mr. Polytropon, have disassembled the drive already,
hence have nothing to loose, try to clean that if you manage to access
that area.

Good luck!


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Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247

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