Truly incredible. The official explanation sounds like something
from a book on Chernobyl. What the heck did the thing use for a
motor? Diesel or Gasoline?
>
>At 04:53 PM 5/2/98 -0400, you wrote:
>>
>>Anyone ever seen a worse failure?
>
>Well, seen after the fact when I was called in to 'repair' it... And
>actually, quite a good thing that no one was there to witness it! (you
>will see why in a moment)
>
>Probably over 15 years ago, NorthStar offered a 14 inch hard drive in
an
>external cabinet for use with the 'Horizon' microcomputers. It was
amusing
>to watch with the top of the enclosure off as the entire unit was
enclosed
>in a slightly smoked brown Plexiglass 'bubble'.
>
>The down side was that the sector wheel/transducer/tachometer assembly
was
>external to the sealed housing and frequently caused "sector not found"
>errors as dust collected on it. This required regular (monthly or so)
>cleaning which required removal of the HDA from the external enclosure
in
>order to access the bottom of the assembly. (quickly rectified by our
>staff after a couple of calls by using a 'nibbler' tool to add a 2"x3"
>opening on the bottom of the external enclosure that we could access
the
>assembly through)
>
>It was also noted in one of the service bulletins that since this
assembly
>also served as the tachometer for the spindle drive, that you could
tell if
>the wheel was becoming dirty by a "surging" sound coming from the unit
even
>if you did not experience sector errors. Little did we know...
>
>We had one customer who tended to keep his system up 24x7 since he had
an
>external sales staff that used the system to file orders and he liked
to
>work from home. (dial-in lines) He also liked to run the HD with the
upper
>part of the external enclosure removed so that he could show off to
>customers and clients just how advanced their operation was. (ignoring
our
>warnings that this would allow the unit to attract dust and dirt more
rapidly)
>
>Well... One Monday morning I get to the shop and we have a number of
>messages on the answering machine (in increasing levels of agitation).
He
>starts off by explaining that Friday evening he started getting
frequend
>'sector' errors reported from the system. Over the course of the day
>Saturday the errors increased and the system response degraded. Sunday
>morning the system would not answer a call at all. Sunday evening he
got a
>call from the Alarm Monitoring company that something had tripped the
>offive alarms. When he went in to check the building, he noted that
there
>"appeared to be a problem with the hard drive" and wanted us out there
>first thing to make sure he did not lose any data.
>
>So... a couple of us went out expecting to have to clean out the wheel
>assembly (yet again) and perhaps correct a couple of glitched
sectors...
>WRONG!
>
>When we entered the computer room, it was quite obvious that there was
a
>bit more than a "problem with the hard drive"!
>
>The room looked like someone had stood in the center of the room with
an
>M-16, and used it to try to cut the room in half. Clear around the
room at
>about table top level were pieces of plastic and metal stuck into the
wall
>boards. The plexiglas 'bubble' from the HDA was gone (obviously
shattered)
>and the platters had large chunks missing from them. No need to even
look
>for the head/arm assemblies.
>
>After an extended discussion with the customer, of which most of the
time
>was spent explaining that we would NOT be able to recover any data from
the
>drive, we set about collecting the wreckage and installing a new drive
and
>software.
>
>Once back at the shop, a call to NorthStar brought a visit a few days
later
>from one of their technical support staff as well as an engineer from
the
>manufacturer of the HDA (Micropolis if I recall correctly).
>
>The "official" explaination went something like this:
>
>Due to the design of the (rather basic) tachometer circuit in this
unit, a
>missing sector pulse was intrepreted by the tach as a loss of spindle
>speed. (start-up mode mentality, if you are starting the drive and
don't
>see a pulse, speed up (or start-up) the motor until the required pulse
rate
>is achieved) This was the cause of the "surging" sound noted in
previous
>service bulletins.
>
>In "theory" (now apparently proven) if the sector/tach wheel became
>sufficiently dirty the tachometer circuit could attempt to keep
increasing
>spindle speed up to such a point where a failure of the unit might be
>induced either by overload failure of the spindle motor or by excess
>vibration caused by excess rotational speed.
>
>Apparently, no one ever considered a 'fail-safe' for the tachometer
circuit...
>
>While they never did detail just exactly what failed first, whatever it
was
>apparently caused a head crash severe enough to fracture one or more of
the
>platters, and from that point it was all downhill...
>
>Without the cover of the external enclosure to contain it, (a metal
>enclosure by the way) when things started to come apart there was
nothing
>to stop it! And the results were indeed quite spectacular.
>
>Made everyone a good deal more serious about keeping those sensor
wheels
>clean... (and the covers on!)
>
>BTW: NorthStar did replace the drive for us...
>
>-jim
>
>---
>jimw_at_agora.rdrop.com
>The Computer Garage - http://www.rdrop.com/~jimw
>Computer Garage Fax - (503) 646-0174
>
>
>
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Received on Sun May 03 1998 - 15:06:53 BST