Fooling with floppy drives - test-drb@ccmp.vtda.org

8 Apr 1999

There are also the "digital" alignment diskettes.  These have certain forms
of misalignment intentionally written to certain tracks in a certain way.
Together with appropriate software, you can ostensibly detect, quantify, and
correct (if you know how and feel you can do it) whatever defects it finds.
I've read about this but never got around to trying it.  I don't know anyone
who's tried it, so I can't even ask the relevant questions.  Dysan made a
whole series of such digital diagnostic diskettes, as they were called, for
various types of disk drives.  Unfortunately, they were priced such that it
was cheaper to buy a new drive than to buy one of these and the software and
fix it yourself.  IIRC the price would have crossed over at about 50 drives,
not counting the labor savings, since I provided that.

The analog alignment process is quite straightforward, but not something I
want to do again.  Moving the heads back and forth, then tightening the
screw holding the lead screw/motor in a fixed position only to have to
repeat the process because the changing stresses from tightening things down
has caused them to move . . . UGH! . . .

Dick
-----Original Message-----
From: Dwight Elvey &lt;elvey(a)hal.com&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Thursday, April 08, 1999 4:53 PM
Subject: RE[2]: Fooling with floppy drives

...
 Steve Robertson &lt;steverob(a)hotoffice.com&gt; wrote:
>
> I've never used the DYSAN alignment disks and would be really interested
to
...
   learn more
about them.

 How effective are they?
 What other tools do you need?
 How much do they cost? 
Hi
 I've used alignment disks. You need an oscilloscope
to use them. You also need to write a low level
driver to keep the system from freaking when doing
the actual alignment check. They record two signals
on the disk that are 1/2 track above and below the
normal track position ( I don't recall what track you
select but as I recall, it is about half way up
the disk ). The two signals are exactly 1 cycle
per revolution of the disk different in frequency.
You look on your oscilloscope at the analog signal
that comes out of the read amplifier and adjust
for what is call a cats-eye pattern. If the track
alignment is right on, you'll have equal height
signals from the first half of the revolution
as the second half ( sync of the index pulse ).
 They also include a constant amplitude track. This
is used to look for contact problems of the disk/head.
One another track they usually have several different
frequency tones recorded. These are used to check the
band pass of the drive.
 Other than the cats-eye pattern, there is usually little
that you can adjust on a finished drive. The cats-eye
pattern can be used to fine tune the stepper position.
There are usually some slotted screws someplace that allow
slight changes in the rotation of the stepper. One does
have to check the proper operation of the track zero
sensor after this adjustment because there is interaction.
 As for price??? I bought the one I have at a surplus
shop for $1.
Dwight