hard disk for unixpc (7300)

[Thad P Floryan]

Re: Stacy's question about use of ST-251 drives in the 3B1/7300 ...

I've installed several ST251-1 (28mS) drives for friends in their systems
and the drive works "fine"; the "fine" is the caveat re: the stiction
problem with not spinning on powerup, but, so far, no ST251-1 drive I've seen
has had the problem.  See below for more details.

For reference, the power supplies in the 3B1 and the 7300 *ARE* different.
Specifically:

The 3B1 power supply is mfd by Power Systems, Inc. and is their model PS 1610-1
(Convergent part number D-65-00056-1, Rev. B).  Its specs:

        90-130 VAC, 245 Watts, 58-63 Hz
        +5 VDC at 20 Amps
        +12 VDC at 5 Amps
        -12 VDC at 300 mA

The 7300 power is also mfd by Power Systems, Inc and is model PS 1569
(Convergent part number D-65-00042-00, Rev. E).  Its specs:

        90-130 VAC, 58-63 Hz
        +5 VDC at 20 Amps
        +12 VDC at 3.5 Amps
        -12 VDC at 100 mA

The ST251 (40 MB) drives use LESS power than the ol' 10 and 20 MB clunkers
that were originally shipped with the 7300, so there's NO cause for alarm
using the ST251 in the UNIXpc.

The San Francisco Bay Area AT&T Users' Group (officially chartered and
sponsored by AT&T, meeting at AT&T facilities) has a number of members who
own UNIXpc systems (I own 4 myself :-)  Beginning in March, the UNIXpc SIG
has its own meeting room (in Sunnyvale) and I'll be showing people how to
open their systems and do various fixes, etc.  Our library includes *ALL*
the docs from AT&T about the UNIXpc, and we're working on getting the source
code to the OS and utilities.  As an elected officer of the group, I'll be
posting more details in the very near future (esp. now that I have more time
since I'm not working 25 hrs/day anymore (as I've been during the past 2
months :-) )

At the February meeting, we had speakers from California Disk Drive Repair
(Santa Clara, CA) who answered ALL questions about HDs, their usage, their
construction, their problems, etc. and I finally got *THE* answer to the
problems with Seagate's drives.  During assembly, disk drive platters are
"wiped" with a chemical that was not being applied evenly, so to reduce the
reject rate the workers were applying MORE material causing a buildup of the
chemical; at "park" position, the "sled" assembly containing the head(s)
"sticks" to the platter preventing main spindle rotation (due to excessive
meniscus).  A quick "whack" to the side of the drive (or manual rotation of
the stepper motor shaft) would "break" the stiction permitting the spindle
to spin up.  There is NO fix to this problem other than another drive.

The "stiction" problem occurs only with certain "batches" of drives, and only
seems to surface after 6 or more months of use (yeah, AFTER the drive's
warranty has expired).  The problem has been noted for both 5-1/4 and 3-1/2
drives.  In all fairness, Seagate is NOT the only manufacturer with this
problem; Seagate's large market share simply causes the problem to be observed
more often with their drives than with other manufacturers' drives.  Sigh.

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