Demagnetising Drive Heads

[kilroy@gboro.rowan.edu (Dr Nancy's Sweetie)]

I recently acquired a 2e for $50, with an disk][ and a half-height drive
made by Mitac.  The latter drive didn't seem to do anything, but I had a
disk][ from my deceased ][+ that I plugged in its place.

I took the Mitac drive apart to look inside it, and discovered a dead bug
shorting out a bunch of contacts.  Removing the bug didn't fix anything.
Figuring that it must have fried some internal component, I just set the
drive in my pile labled "Computer Literacy Show & Tell".  (That class goes
better when you can show the students real examples of what you're talking
about.)


I got LifeSaver from Follett software.  (I'll take a moment to say that
whoever wrote it knew a lot about disks, but should have though more about
the user interface.  It's worth a try if you have a damaged disk.)  The
program has recovered most of my disks pretty well, but I noticed a pattern
on some of them.

Basically, all the disks that I tried to catalogue in the Mitac drive have
erased catalogues and neat spirals of bad sectors.  The LifeSaver screen
draws a grid of sectors, arranged in column by track.  The bad sectors on
these disks make nearly-perfect diagonal lines.  That is, the bad sectors
are in a pattern that one would expect if the head was writing garbage and
moved across the turning disk.

The disks I tried to boot in the Mitac drive have track 0 completely blank,
along with a similar diagonal pattern.

Is it plausible that the deceased bug caused a short which magnetised the
drive head but did no permanent damage?  If so, then it seems that if I
could de-magnetise the head (and test the drive on a disk I don't care
much about), then it could re-enter service.  It's not a high priority,
but I just hate to let a piece of hardware go when it might be easy to fix.

Presuming this is worth trying, does anybody have suggestions on how to
proceed?


Darren F Provine / kilroy@gboro.rowan.edu
"Unfortunately, most programmers like to play with new toys.  I have many
 friends who, immediately upon buying a snakebite kit, would be tempted to
 throw the first person they see to the ground, tie the tourniquet on him,
 slash him with the knife, and apply suction to the wound."
                               -- Jon Bentley, _Writing Efficient Programs_