[vcf-midatlantic] Drive repairs, was Hard drive art

Jason Perkins perkins.jason at gmail.com
Sun Apr 21 17:04:25 EDT 2019

Some drives (Apple Widget, Plus Hardcard / Quantum) had a fine position
sensor on the head arm. The Lisa disk uses this during a low level format.


On Thu, Apr 18, 2019 at 10:35 PM David Gesswein via vcf-midatlantic <
vcf-midatlantic at lists.vcfed.org> wrote:

> On Thu, Apr 18, 2019 at 10:24:47PM -0400, Dave McGuire via vcf-midatlantic
> wrote:
> >   But if we're rewriting the servo tracks anyway, it won't matter,
> > unless we're trying to recreate them to align to existing data.
> > Otherwise they can be anywhere, and the other tracks will follow suit
> > when the drive is low-level formatted.
> >
> If its a voice coil servo drive I'm not sure how you would get the track
> at
> uniform spacing without some sort of measurement and feedback.
> >   I guess the question is whether we'd do this to recover the
> > functionality of a drive or recover the data from a drive.
> >
> I've heard of the degaussing to erase packs problem. I haven't seen
> bad servo tracks as the reading problem. Is normally some mechanical shift
> so when the servo has the servo head centered some of the heads aren't
> on track. Pulling the servo loop method I linked to in the first posting
> is
> the easier way to recover the data. I also had tracking problem when I did
> a
> board swap to recover a drive. The replacement board servo null was
> physically off from the original.

Jason Perkins
313 355 0085

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