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Subject: Re: Hard drive spins with variable speed ... phase damage????
X-Newsreader: Microsoft Outlook Express 5.50.4920.2300
Date: Tue, 03 Dec 2002 16:22:35 GMT
NNTP-Posting-Date: Tue, 03 Dec 2002 11:22:35 EST
Organization: Cox Communications
"nicolas" wrote in message
> I need to rescue the data of a SCSI drive (Quantum Viking II 9.1GB
> 7200 rpm). It seems the disk has a problem with the motor because I
> can hear it spinning at one speed and then it slows down to another
> speed, and then again it goes up, and then down again. From what I
> have read it could be that one of the motor phases have damage, and
> thats why the motor canīt reach itīs 7200 rpm.
> To open the drive I can use a laminar clean bench at my university. My
> doubt is the following: Can I speed the motor myself with another tool
> and make the disk reach the 7200 rpm and then make an image of the
> drive to another disk? Is that possible? Should the disk spin at 7200
> rpm exactly ?? or will it work at 7000rpm or 7500rpm for example??
> Thanks for your time, I appreciate any help.
> Sorry for my english but it is not my native language. (I am from
I wish everyone had your command of English, Nicolas.
The read channel contains a PLL that needs to lock to the data being read
from the drive. The pull-in range of the PLL used to be spec'd at 2%, but
it's often less than 1% these days. This isn't generally a problem in a
working drive, since the motor speed is accurate to better than 0.1%. Since
the data rate is proportional to the motor speed, you'll need to keep the
motor speed within roughly 1% or the PLL won't lock to the data, and you
won't be able to read.
A second issue is vibration. The track density on modern drives is pretty
high, and I wonder if attaching a mechanical drive shaft to the disk stack
will cause severe enough vibrations that the servo won't be able to track
the lateral disk movement. I don't know the answer to this, but in a modern
drive the track spacing from center to center is only a few microns (and I
think it's less than 1 micron in new drives), so any mechanical bump
delivered directly to the disk stack would potentially cause the servo to
-- Mike --
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