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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Hard drive spins with variable speed ... phase damage????
Date: Tue, 03 Dec 2002 16:41:36 GMT
NNTP-Posting-Date: Tue, 03 Dec 2002 08:41:36 PST
> "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 can=B4t reach it=B4s 7200 rpm.
> > To open the drive I can use a laminar clean bench at my university. M=
> > doubt is the following: Can I speed the motor myself with another too=
> > 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
> > Chile).
> I wish everyone had your command of English, Nicolas.
> The read channel contains a PLL that needs to lock to the data being re=
> from the drive. The pull-in range of the PLL used to be spec'd at 2%, b=
> 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%. S=
> the data rate is proportional to the motor speed, you'll need to keep t=
> motor speed within roughly 1% or the PLL won't lock to the data, and yo=
> won't be able to read.
Pull-in range is a minor problem since all of the read channels I have
seen in recent years use zero phase restart. This was mainly due to the
wider tracking range required by zoned bit recording. That is, data rate
depends on disk speed and radial head position. The disk is divided into
radial zones each having a different data rate (near constant linear
> A second issue is vibration. The track density on modern drives is pret=
> high, and I wonder if attaching a mechanical drive shaft to the disk st=
> will cause severe enough vibrations that the servo won't be able to tra=
> the lateral disk movement. I don't know the answer to this, but in a mo=
> drive the track spacing from center to center is only a few microns (an=
> 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 =
> lose lock.
The drive will attempt to read with worse tracking than it will allow
for write but the spindles are usually supported by both the top and the
bottom cover. The drive is likely not to function if the top cover is
removed because of servo problems. The last cantilever drives I saw were
early 1990's and they were flakes.
If the data must be recovered, there are companies that do this
sometimes by putting the disk stack to be recovered into another drive.
This is a clean room operation. Laminar flow benches are OK but not good
... The times have been, =
That, when the brains were out, =
the man would die. ... Macbeth =
Chuck Simmons firstname.lastname@example.org
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