🚀 go-pugleaf

John R. Levine asks:

>I have a 3.5" 1.44MB floppy drive on my EISA 486 PC which is getting read
>errors on disks I have reason to believe are good, so I expect that the heads
>are out of alignment.

>What's involved in realigning them?  It is my vague recollection that I've
>occasionally seen do-it-yourself alignment kits advertised containing a
>reference disk and some kind of software.  Are they for real?

Yes, John, these "digital" alignment disks and software exist, and
they do work. Alignment of drives usually consists only of setting
the base (radial) head position - the head azimuth angle is not,
in my experience, adjustable. The alignment disk is created specially
with varying degrees of MISalignment built-in to the tracks and
sectors. Along with the disk is a usually a table specifying the
amount (+ or -) of radial misalignment in each of a number of tracks,
usually with the first few sectors written "correctly", and further
sectors written with progressively "worse" errors. 

The trick is to attempt to read the disk in raw track/sector addressed 
mode, and report exactly which sectors fail to read without error. 
If the head is properly aligned, the first two sectors to fail will have
the same absolute error, one + and the other - from nominal. If
the head (positioner, actually) is a bit off, one failure will be
at a greater or lesser error value than the other: +10 & -15, for
example. You then back out the screw(s) holding the positioner
motor down and rotate it SLIGHTLY to extend (in this example) or
retract the head a tiny bit - resulting in the failures being
at, say +12 & -12. This is then repeated for several tracks,
usually one near the edge, one near the innermost tracks, and one
in the middle. The error is kind of "spread around" to give
the best average alignment... Another track or set of tracks
allows you to check for head azimuth error in a similar fashion,
but as I said, you probably cannot adjust it.

All that having been said, have you tried a *really good*
cleaning? I had one 3.5" drive that seemed to have been contaminated
(Coke, I believe!) and it took 5 or 6 successive cleanings before
it started working right...

Dave
dbell@cup.portal.com