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

[Dave McGuire]

On 4/22/19 7:39 AM, David Gesswein via vcf-midatlantic wrote:
>> 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.
>>
> Found picture of the drives online. Looks like they used an optical position
> sensor similar to how my RK05's work. This was probably the last gasp of
> that method before the track density got too high for it to work.
> 
> Are you saying the Widget only uses it to format? How does it determine
> head position during normal operation? For my RK05 its always uses the
> optical sensor for positioning the heads.

  It's only for relative position; the quadrature approach cannot
"unwrap" the phase.  The drive logic must have a general idea of where
the heads are, by counting the sine/cosine phase wraps as they cross 0
degrees as the head carriage moves.

           -Dave

-- 
Dave McGuire, AK4HZ
New Kensington, PA