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| Author |
Message |
alan
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IBM PS@/70 hard drive needed.
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Oct 4 13:35 UTC 1995 |
IBM PS2/70 hard drive needed. Must not have been repaired or 'spun'
to restore speed. Please ms on grex or alan509@umcc.umich.edu, respond here
or 668-1535. Oh yes, I've already been to property disposition. Thanks!
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| 26 responses total. |
mdw
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response 1 of 26:
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Oct 22 00:57 UTC 1995 |
'Spun'? Say what?
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alan
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response 2 of 26:
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Oct 29 15:50 UTC 1995 |
Spun means that the drive has developed 'stiction', meaning that there
is a microscopic lube film on the platter that somehow - heat and age? -
grabs the heads and will not allow the platters to spin. The temporary cure is
to hold the drive and rotate it violently and then stop fast hoping that the
momentum of the initial movement will cause the platter to rip loose. Then it
might work for some unspecified amount of time. You could also reach under the
control board and physically spin the counterweight to get the thing going. I
actually found a 60 mb plug compatable new conner drive for $100 and my friend
who had this problem is happy.
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ajax
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response 3 of 26:
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Oct 29 16:21 UTC 1995 |
Yikes! I've heard of cars that needed a push, but disks!? {:-)
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n8nxf
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response 4 of 26:
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Oct 29 20:52 UTC 1995 |
I have a 40M Western Digital IDE with this problem. It's been running
on my bbs for about 3 years without problems now. I just have to keep
it running.
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scott
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response 5 of 26:
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Oct 29 23:41 UTC 1995 |
This is where "head parking" comes into play. :)
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gregc
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response 6 of 26:
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Oct 30 09:02 UTC 1995 |
I doubt that "stiction" is caused by "a microscopic lube film on the platter
that somehow grabs the heads". Are you familiar with the term "head crash"?
*Any* contaminant on the platter that exists in a large enough quantity to
grab the heads would result in an immediate head crash when the unit did
spin up. More likely, this is due to sticking in the *bearings*. In fact,
very likely, as that is a commonly observed symptom of dirty bearings.
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n8nxf
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response 7 of 26:
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Oct 30 12:58 UTC 1995 |
Nope. It's not the bearings. Most HD's allow their heads to rest on the
surface of the platters when the drive is not spinning. They drag along
the sufface on spin-up untill the platters are spinning fast enough so that
the heads "fly" on a cushion of air thats moving along with the spinning
platters. Some drives have a mechanical device that lifts the heads off
the platters whenever the drive isn't spinning at speed. These are common
in notebooks wich often have a power-saving feature that turns off the
drive if it hasn't been accessed in a given amnt. of time. This is done
to give the drive a reasonable life expectancy despite the cyclic
operation.
I don't know if the sticking problem is caused by a thin sheet of oil
that's leaked past the bearings or not. It sounds reasonable. Two
very clean and very flat surfaces will also skick to oneanother quite
well.
Head crashes are when the head picks up a bit of the platter (or whatever)
and proceeds to rub up more and more of the magnetic platter coating.
The problem is easy to spot when the HD is pulled apart. the plater will
have concentric rings of coating rubbed off. This is a common problem
whenever two materials moving at different speeds contact without
lubriacation.
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alan
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response 8 of 26:
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Oct 31 03:23 UTC 1995 |
Right, Klaus!
According to the book "Upgtading and repairing ps's' the glass to glass
reference is mentioned. There is also something about a 'goo' or
film which may refere to micron type magnetic material. We are talking
nuance here.
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gregc
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response 9 of 26:
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Nov 1 11:46 UTC 1995 |
Klaus, I have used, worked on, disassembled, and repaired more types of
disk drives that most people have relatives. I *know* how they work, and
I don't buy the "film on the platter" explanation. Very few drives these
days have head lift mechanisms.Almost all drives are "contact start/stop"
winchester technology thin-film heads. Yes, the heads "fly" above the
platter, but that flight separation is measured in *microns*. A head crash
is caused by *anything* that causes the heads to recontact the surface
at operational speeds. 2 very flat surfaces will also bond to each other
from vacuum pressure, but while the platter is *very* flat, the heads are
not. The have a very slight curve to prevent this problem and also to
create the airfoil effect that allows them to fly.
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alan
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response 10 of 26:
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Nov 1 17:22 UTC 1995 |
So, What really happens? I'll bet there are thousands of IBM pc computers
that have this problem and are on a shelf because of the high cost
of a proprietary replacement. Pity.
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n8nxf
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response 11 of 26:
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Nov 2 14:36 UTC 1995 |
I have the same question. I don't buy the sticky bearing explination
for most cases. My drive with this problem makes a definate "klink"
ringging noise when I have to pushstart it. Sounds very much like the
head/s have stuck to the platter. I'll find out when this drive becomes
a paper-weight.
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alan
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response 12 of 26:
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Nov 2 21:45 UTC 1995 |
You probably read the part about some drives having an outboard brake which can
be removed if it is sticking in the locked position.
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n8nxf
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response 13 of 26:
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Nov 2 22:09 UTC 1995 |
Not this one. It will spin up fine if it's still warm. Alow it to cool
for a few hours and it will stick 70% or the time.
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mdw
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response 14 of 26:
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Nov 7 12:10 UTC 1995 |
There was a generation of seagate problems that definitely had problems
with stiction. I know I read an explanation of at least once, so I
assume it's accurate. If I recall right, the stuff they put on the
platter isn't just magnetic oxide, it's actually a very complicated
witches brew of many layers of adhesives, oxide, and "stuff". One of
the last layers to go on is a lubricant, which is there to make contact
start/stop operation possible. In the case of stiction, at least for
the seagate drives, the problem is that they put on just a *tad* too
much - and, instead of staying all in one place, as the drives were
used, the film very slowly started to migrate out, and get just a hair
thicker in the landing area on the disk. It's a microscopic difference,
I gather, but it's all because the lubricant isn't, in fact, a solid,
but a liquid, so it flows, however slowly. I don't know what they use
for motors on these things, but I can well imagine they don't have much
starting torque. It might not take much extra "stiction" at all to
exceed the starting torque.
Interesting irrelevant fact - ordinary glass isn't a solid, but a
supercooled liquid. Because it's, in fact, still a liquid, it flows,
very slowly. In very old window glass, you can see the sag lines in the
glass.
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gregc
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response 15 of 26:
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Nov 7 12:23 UTC 1995 |
Ok, Marcus, thanks. That makes more sense. If the lubricant was orriginally
designed to be there, then it's not a foreign substance. My impression,
from the earlier posts, was that this lubricant was a foreign substance that
had crept out of the bearings.
Urban legend update on irrelevant fact:
Yes, glass is a supercooled liquid that is still considered to be in the
liquid state, just with a *very* high viscosity. However, it turns out the
creep rate is far less than originally thought, Alot of big old glass store
front windows, like the ones in Macy's in New York, were measured and found
to be thicker at the bottom and it was assumed this was due to flow. However,
I was watching something on PBS a few months ago about glass production and
the history of glass. One of the "experts" stated that large window pain
glass was *always* made with the bottom edge thicker for strength. It was
*manufactured* that way! In fact, they found several cases of old store
front windows that varied in thickness from side to side, and even some that
were thicker at the *top* because they had been incorrectly installed.
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n8nxf
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response 16 of 26:
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Nov 7 15:19 UTC 1995 |
That does make a lot of sense Marcus. I was wondering if there was a some
sort of lubricant put on the platters.
I've heard the same thing r.e. glass. Matter of fact, we have some pains
in our house where the ripples in the glass are vertical. If glass were
moving around like a liquid I would have expected more problems in precise
optical devices with time.
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gregc
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response 17 of 26:
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Nov 9 21:50 UTC 1995 |
Good point, 2 of the biggest refracting telescopes in the world, the Keeler
in Pittsburgh, and the Yerkes, both have 40" objective lenses and are both
about 100 years old. While dated, they are both still considered fine
instruments, and I know that as of at least 1979 the Keeler was still being
used to do real science. Optical lenses have to be accurate to at *least*
1/4 wavelength of light, about 150nm, if the glass does creep, you'd think
it would have moved at least that much in 100 years.
Now, I know optical glass is made from something alot different from ordinary
window glass *today*, but I don't know what they were using 100 years ago.
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mdw
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response 18 of 26:
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Nov 26 02:14 UTC 1995 |
Not necessarily stuff too different from what they use today. Ordinary
glass melts at a much lower temperature, and also has a much greater
thermal expansion factor. Thermal expansion would be a bad thing in a
telescope, because in order to point them at the sky and do real
science, you have to essentially open a large barn door and point the
telescope outside, and you're generally up a mountain and the sky is
clear, so there's a vicious thermal cycle there. So, instead of glass,
you'd be wainting to use something more like nearly pure silicon
dioxide, ie, quartz. Pure quartz is murder to work with (because it
melts at a much higher temperature), but for ordinary heat properties,
it's marvelous stuff, and puts pyrex to shame. There's another reason
to use something like quartz in a refractor - it turns out that ordinary
window glass is opaque to uv, whereas quartz transmits it. Since the
quartz would be a lot more super-cooled, it would probably creep a lot
less than window glass would as well.
I believe that I've heard that for solar telescopes, as well as high
power laser work, one of the things they like using for lenses is
ordinary table salt. Apparently, table salt is a lot more transparent
than silicon dioxide (and, of course, it melts at a much higher
temperature). That means you can do a much better job of spectroscopy,
and that in the case of the laser, the lens doesn't melt or waste as
much power.
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gregc
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response 19 of 26:
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Nov 26 12:22 UTC 1995 |
I seem to remember that the 200" Palomar mirror is made of a form of Pyrex.
Yes, I know that alot of modern optics is made from Quartz, but I'm
skeptical that they had the technology to make a 40" refracting objective
lens out of quartz in the 1800's.
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mdw
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response 20 of 26:
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Nov 29 06:27 UTC 1995 |
I'm sure they had the technology. Quartz occurs naturally in nearly
pure form, is well-known from ancient times, & only requires great heat
to work. Now, whether they bothered to use it, or had a lower-cost
alternative, I don't know. Certainly, however, optical engineering was
already well developed by the 19th century.
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n8nxf
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response 21 of 26:
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Nov 29 15:00 UTC 1995 |
(I once helped build a torch for cutting quartz tubing. I was C shaped
with a dozen stainless tubing fingers pointing towards the inside. It
was a pre-mix design (fuel and oxidizer mixed in the torch instead of at
the burn point.) and burned hydrogen and oxygen! I was one hot mother
and we had to play with the stainless tubing size till we found a size
that was just large enough so the cooling effect of the gas going through
tubing would keep the tubing from burning back. One also had to be carefull
that you ran it on the fuel-rich side!! It was very pretty to see in
operation too.)
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gregc
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response 22 of 26:
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Nov 29 16:35 UTC 1995 |
I'll bet you guys burned up alot of stainless tubing before you got it
right?
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n8nxf
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response 23 of 26:
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Nov 29 16:42 UTC 1995 |
A few. I made three trips to the Pharmacy on the corner for syringe
needles before we got it right. I wonder to this day what they were
thinking about me...
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alan
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response 24 of 26:
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Nov 30 05:32 UTC 1995 |
what the heck is this:
Respond or pass?
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