Fooling with floppy drives

From: Dwight Elvey <elvey_at_hal.com>
Date: Thu Apr 8 17:45:38 1999

Steve Robertson <steverob_at_hotoffice.com> 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
Received on Thu Apr 08 1999 - 17:45:38 BST