Date   : Thu, 19 Jul 1990 17:00:42 GMT
From   : entropy!dataio!shiloh!fnx!del@beaver.cs.washington.edu (Dag Erik Lindberg)
Subject: How do I align a disk drive?

I already posted this once, but I think it crashed because of a
non-existant group comp.peripherals...

In article <XX000118c2@pallio.UUCP> dg@pallio.UUCP (David Goodenough) writes:
>I recently got an old computer with a pair of full height 5.25" drives in
>it. One of them is out of alignment because disks formatted in this drive
>can't be read by the other (or any other 5.25" drive in the house), and

Several people have recommended checking the drive rotational speed.
Certainly try that first (I recommend using a flourescent light if there
is a timing disk on the hub pulley underneath the drive).  There will be
a 10 turn potentiometer on the motor control board to adjust the speed of
the motor.  Don't adjust the wrong one if there is no separate motor
control board.

If you really need to align the drive, you will need an alignment 
diskette.  This is a specially recorded analog diskette which cannot
be duplicated by regular (digital) drives.  You will also need an
oscilloscope which can invert one channel and add the two channels
together to produce a single trace on the screen.  This is not 'x-y'
mode, but a regular sweep mode with the two channels summed together.
Connect the two probes to the differential inputs from the drive side
1 preamplifier and sync the sweep on the index pulse.  Insert the
alignment diskette, start the drive and step to track 16. Adjust 
your scope and you will see a pattern on the screen resembling a 
pair of cats eyes, or a butterfly if you prefer.  The idea is to 
loosen the retaining screw on the stepper, and move the head until 
the two 'lobes' of the pattern are as close to the same height as 
possible.  Tighten down the screw and make sure the pattern hasn't
changed (this will probably take a few tries till you get the hang
of it).  Now unload the drive head so you can move the scope probes
to the side 2 preamplifier and check the alignment of the other
head.  It is extremely rare that head 2 will be out of alignment
with head 1, but if it is, you're in trouble.  There is no good
way to adjust head 2, as it is (usually) simply screwed to head
1 and you will have to remove the aligment diskette, make a blind
adjustment, and take a reading to see if you hit the mark.

If you feel like you want to go through with this, I can get you the
part number for the alignment diskette. Heck, I might just send you
mine, since I no longer feel it is cost effetive to align 5.25"
drives.  The whole procedure is likely to take you a couple of
hours if it is your first time, and replacement drives can be had
for $50.  Incidently, if you buy an alignment diskette, it will
cost you $35.

-- 
del AKA Erik Lindberg                             uunet!pilchuck!fnx!del
                          Who is John Galt?