mrhagger@athena.mit.edu (Michael R Haggerty) (11/01/90)
Summary:
I was able to add an 84MB 3.5" SCSI hard disk drive to my IBM PS/2 Model 50
in floppy bay B, leaving my original 20MB drive in place. The fit is not
wonderful, but I am satisfied with the results. Prerequisites: PS/2 Model 50
with empty floppy bay B and blank faceplate for that bay, Microchannel SCSI
controller that includes a power connection, 3.5" SCSI hard drive, "skid"
(to be modified--see below) for mounting hard drive, 50-pin ribbon cable,
4-pin power cable.
Suppliers: (usual disclaimers apply)
$389.00 Seagate ST-1096N 84MB 20ms SCSI hard disk, 5.25" disk with
Disk Manager
and $249.00 Future Domain MCS350 Microchannel SCSI controller, 50-pin
ribbon cable, 4-pin power cable, 3.25" disk with hardware
driver software
both from: Dirt Cheap Drives ("DC Drives")
1110 Nasa One, Suite 304
Nassau Bay, TX 77058
1-800-872-6007
(See, for example, ad in _PC_Sources_, Oct. 1990, p. 457)
(about $10) Plastic "skid" for mounting hard drive
from: PS Solutions, Inc.
13745 Omega
Dallas, TX 75244
1-214-980-2632
I don't know about the possibility of getting a blank faceplate if you don't
already have one. I was "fortunate" to have bought a computer with only
one floppy drive, so I already had the blank. I also don't know how applicable
this procedure is to other Microchannel Models; I understand even the 50Z has
a different built in hard disk controller (not that that will matter either;
I just don't know).
Gory Details:
Although the salesman from DC Drives wasn't the most knowledgable in
the world (which salesperson is?), I didn't have any trouble ordering from
them. They also seemed to have a large selection and good prices.
I paid $18 for second day air, and the package indeed arrived intact
two days later. At first the salesman recommended buying a "kit" including
the aforementioned items plus, apparently, additional software. Eventually
I realized that I didn't need to fork out the additional $100 which would
have (apparently) only given me added support for unix, xenix, etc. which
I don't yet use anyway. The kit didn't claim to contain mounting hardware;
their assumption was that I was replacing my 20MB drive and would reuse the
rails from it. In fact, few people I spoke to at any of dozens of companies
suggested ADDing a hard drive; most recommended replacing the old one.
The woman I spoke to at PS Solutions (Jacqueline Green), on the other hand,
was very helpful and knowledgable. She works for what seems to be a tiny
company which manufactures these skids for other manufacturers. She claims
that (now that I've made a suggestion for change) that they will modify
the skids themselves and send them out "probably for $10."
Even ignoring problems with the skid, the drive is a tight fit in floppy drive
bay B. A connector (which would be used for floppy drive B) on the back of
the bay protrudes into the bay and touches the top rear of the drive. The
hard disk's own connector is on the bottom of the drive, so luckily it doesn't
conflict with the computer's floppy disk connector; if it did, the job would
have been impossible.
As it was, the drive, when snug against the connector, had just enough
clearance for the cover to be installed. It is a tight fit, especially
considering that the ribbon cable must also fit between the rear of the
drive case and the floppy connector.
I considered desoldering and removing the floppy drive connector to make more
room. I may have attempted it, as the connector sits on a very simple circuit
board (no components at all) with the connector for drive A, and removing it
would have provided about 1/4" more clearance. If I had done that, the ribbon
cable connector plugged onto the hard drive would have been the new
constraint, as it would have hit the naked circuit board. But in fact even
with this configuration, it would not have been possible to engage the skid
in the locking groove with the hard drive screwed to it (except possibly by
getting a thinner 50-pin connector). It was not possible to completely remove
(i.e. saw off) the unused right half of this circuit board, because the traces
which lead to the drive A connector pass through the drive B side. As I was
nervous about wielding a soldering iron to my poor computer if not necessary,
I sought other possibilities.
Finally I latched the new skid into place on the rails, and placed the hard
drive loosely on top of it as far back as possible. I marked the location
where the drive holes would have to be, and added my own holes to the skid.
In the end, the holes I needed to add (marked as "x" on the sketch) are
located 1/2" closer to the front of the skid than the original holes (marked
"*"). The holes marked "o" are not used and do not enter into the discussion.
+-----------------------------------------+
| o o |
| * x * x| You must make holes marked x
\ +-----+ +-----+ | yourself. Position them 1/2"
-----+ +----+ +-+ +---------+ forward of the holes marked *.
<--> | | <--> <-----------------
1/2" | | 1/2"
bottom view of skid | +---------+
(out of proportion) | || |
| latching || |
| || |
| ridge-->|| |
| || |
<---rear front--> | +---------+
of computer | |
| |
-----+ +----+ +-+ +---------+
/ +-----+ +-----+ |
| * x * x|
| o o |
+-----------------------------------------+
<--> <-->
1/2" 1/2"
With the given modifications, the drive can be mounted on the skid and the
skid can by clicked into the computer.
Finally, I reinstalled the blank faceplate from floppy drive B and put the
cover back on. The cover pushes lightly against the new hard drive, which
pushes lightly against the floppy drive connector at the back of the bay, but
I think it is an acceptible situation (i.e. there is not significant strain
against the components, and the possible loss of shock absorption is probably
not too bad). Everything seems to work just fine.
As I mentioned before, I am suggesting to PS Solutions that they add the four
requisite holes to their design. Perhaps (if indeed many of you
are interested) a spate of interested phone calls will persuade them to
indeed do this mod. In any case, it's not a big deal to add the holes
yourself.
Discussion:
I am satisfied with this solution. I do not consider it a particularly clean
installation, in view of the tightness of the fit. Nevertheless, my solution
is by far the most economical way to boost the hard drive capacity of a
Model 50, and has the advantages of being internal, leaving the current drive
installed, not requiring any modifications to the computer unit, and leaving
open the possibility of further expansion on the new SCSI controller. This
solution, leaving me with a fast 84MB plus the original slow 20MB, is cheaper
than any other options I found, even those leaving me with a net of only 60MB
of slow storage. For even less money, one could add on a lower (21MB, 32MB,
or 60MB) capacity drive, and there is a more expensive 3.5" 105MB drive
listed as well.
If anybody uses this information to advantage, my philanthropic side would
be stroked if you drop me a note letting me know I was of assistance.
Michael Haggerty
mrhagger@athena.mit.edu