Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!portal!cup.portal.com!thad
From: thad@cup.portal.com (Thad P Floryan)
Newsgroups: comp.sys.amiga
Subject: Re: Seagate \
Message-ID: <20538@cup.portal.com>
Date: 17 Jul 89 11:35:53 GMT
References: <4638@crash.cts.com>
Organization: The Portal System (TM)
Lines: 82

More from our "anonymous" poster forwarding other people's responses (indented):

	Let me jump in here: I worked at a plant where we plated magnetic
	coatings onto platters and drums for computer drives. The company I
	worked for also built the heads that were used. I cannot believe
	Seagate would have people manually applying a "lubricant" onto the
	disks with "rags".
	            ^^^^
How about "linen cloth"?  THAT's what they use; my term "rags" was not meant to
conjure up visions of a back room full of grease-monkeys in dirty overalls! :-)

	We used to plated coatings as thin as .000005" (that's 5 millionths of
	an inch!), this was less than the surface finish RMS (roughness
	measurements) and ANY other substance visable on the surface was
	grounds for rejection (the disk). Most of the plated media didn't
	require "lubrication" (one exception was the drums used in the
	Minuteman Missle system....it had a Rhodium top plate) but when they
	do it's generally hard Chrome plated about 25 microinches...anyways,
	what I have to say is just a tiny bit of dust in ANY type of wiping
	material will scratch a platter something fierce...I know, I've
	scraped a few in my time..... 

I doubt the "plated media" in MODERN drives possessing Whitney-arm, thin-film
heads is Chrome; the magnetic properties are inadequate.  "CrO2" media on audio
tapes is not "Chrome", it's chromium dioxide and colored black; "normal" audio
media is ferric oxide and "rust-colored"; the Seagate drive I opened (see below)
has a bronze-colored media with a chemical coating (lubrication).

Whatever the disk drive "plated media" material IS, it's unbelievably hard.  I
opened one of my defective ("stiction") Seagate ST251 drives and performed some
experiments on it:

1) lightly touching the platter surface with a screwdriver blade while the disk
   was spinning left NO evidence of the contact.

2) blowing cigarette smoke onto the platters while running DiskPerf caused no
   noticeable effect.

3) spitting onto the rotating platter during DiskPerf (yeah, I'm really getting
   mean here! :-) brought up a R/W error requestor; manually spinning the shaft
   and moving the head assembly while wiping the platter with a Kleenex (tm)
   soaked with Ronsonol (tm) lighter fuel cleared up the R/W error as verified
   by another DiskPerf run.

4) depositing a fingerprint on the platter, manually spinning the main spindle
   shaft, and positioning the heads so they'd ride over the fingerprint, a VERY
   noticeable drag was encountered at the point of contact with the fingerprint.
   Continuing to spin the main shaft, the heads eventually erased all evidence
   of the fingerprint; the drive didn't pass a DiskPerf until I again cleaned
   the platter (and, by implication, the head) with Ronsonol.

5) my home microscope only goes to 100x, so I couldn't see the "white worms"
   as I did at the HD repair place.  But careful examination of the drive
   clearly shows the "heads" ARE in contact (buffered by the lubrication) with
   the platter surface during normal operation (determined by sighting across
   the disk surface looking into a high-intensity lamp).  The head sled is a
   rectangular block about 1/8"x1/4" and about .050" thick, whose R/W surface
   is as super-polished as the surface of the platters.

6) Final experiment: moved the heads to PARK position and waited awhile; there
   was VERY DEFINITE RESISTANCE ("stiction") when attempting to move them later.
   Moved the heads to the middle of the platter and waited awhile; there was NO
   noticeable resistance when attempting to move them later.

The anecdotes posted by our "anonymous" poster tend to suggest "old" disk
technology, pre-Whitney and possibly pre-Winchester; not relevant TODAY. 

The "stiction" problem with the drives is one characterized by physics and NOT
by chemistry; more specifically: fluidics.  If you haven't done so already, do
the simple experiment I described in the previous posting on this subject (with
the two glass plates (or microscope specimen slides) and a drop of water).

And, for everyone's entertainment, amusement and enjoyment, I'll bring the drive
to this week's BADGE meeting where we'll attempt to induce a head crash after
everyone's had a chance to SEE the insides of the drive for themselves.  Try to
dream of a way to make it fail; I've already dropped it and wacked it on the
side with a wooden mallet while it was operating ... it continues to function
after clearing the momentary R/W error.  As I've said before, the basic design
of the drive IS good, it's only the manufacturing flaw regarding lubrication
that is causing all the problems.

Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]