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A Second Hard Drive for the Tandy 1000HD
Back in December of '85 I bought a 1000A HD (cat. #25-1001A), to which I
subsequently added RAM to bring its total to 640K, the RS-232 piggyback card
to the existing Memory Plus board and, more recently, the 286 Express Card,
made by PC Technologies and sold by Tandy. The computer has been utterly
reliable during more than two years of constant usage and my chief concern of
late has been the lack of adequate space remaining on that 10mb hard drive.
Initially, 10mb seemed like an awesome amount of storage but with the 1000
being used for so many different tasks I frequently have been forced to
download less active files to floppies in order to maintain enough working
space for things like program development and word processing files. This
prompted a search for a way to add an extra hard drive to the machine at a
reasonable cost. One way would be to get an external hard drive like the one
that Tandy sells for around $700 with an extra charge for the necessary cables
and modification to the HD controller. A more attractive option seemed to be
a "hard card" with the idea that it would replace the installed HD controller
card and the hard card's controller would run both its own drive and the
1000HD's existing 10 megger. So, I started looking through the ads in several
of the computer magazines.
The full page ad of Discount Computer Supplies (DCS) of Athens, OH in
recent issues of 80 MIcro caught my eye right away. DCS was offering a $395
30mb hard card specifically for the Tandy 1000's. The photo in the ad showed
a Western Digital controller with the necessary connectors for controlling two
drives. Great! My first concern was whether the computer's power supply
could handle a second HD, given that the 286 Express card was already using
7.5 watts in addition to the full memory load and the existing HD. I called
DCS and learned that their hard card needed only 10 watts. A call to Customer
Service in Fort Worth revealed that the 1000HD's power supply was capable of
running TWO 17 watt hard drives in addition to everything else. Delightful!
I'd end up with 40 megabytes of total HD capacity at a very reasonable cost.
Well, not quite....
I called DCS to place my order, explained to one of their techs that this
would be a second hard drive for the machine, described my current
configuration, and asked for the cabling that would allow the hard card's
controller to run both drives. It was fortunate that I talked to a tech
because I found out right away that the DCS 30mb's controller wasn't
compatible with the 1000's 10 megger. It turns out that the 30 megger is RLL
encoded (a high density format) and the 1000's HD is MFM encoded (about 2/3 as
dense as RLL). The best that DCS could offer was a 20mb hard card, which uses
exactly the same drive mechanism but is encoded in the less dense MFM format
and its Western Digital 1002A-WX1 controller IS compatible with both drives.
I asked if the 1000's 10 megger, a Tandon TM-252, could be reformatted with
RLL encoding. The tech said it was doubtful and there was a danger that it
might destroy the drive as it wasn't designed for that kind of operation.
Rather than take a chance on wrecking what has been an extremely reliable
drive I decided to order the 20 megger along with the necessary cables. After
all 20 + 10 for a total of 30mb isn't too shabby either and the 20 megger was
slightly cheaper at $375. A few days later the UPS delivered the eagerly
awaited package and then the fun began...
The DCS hard card consists of a FUJI FK309-39R drive module and a Western
Digital 1002A-WX1 controller card mounted on a metal backing plate such that
the whole unit can be plugged into the right hand slot of a 1000A with the
drive mechanism overhanging into the empty space between the card area and the
support structure for the floppy drive and 10mb hard drive. It seems to be a
very solid well-constructed unit. The controller card's IC's and components
with the exception of the drive parameter ROM, are all of the tiny surface
mount type, making the card quite short. The controller was attached to the
metal plate with 1/4" spacers and the drive was mounted on 5/8" spacers. Also
included in the kit were two 20 conductor ribbon cables, one to go to each
drive from the appropriate connectors on the controller, a power cable with a
"Y" junction and one 34 conductor "daisy chain" ribbon cable to go from the
controller to each of the drives. A group of five conductors between the
center drive connector and the end drive connector had been twisted 180
degrees to take care of drive selection (more about that later). There was
also a few pages of rather minimal installation instructions and a floppy
diskette containing only a format program for RLL drives (obviously not
needed). The controller came set for the IRQ2 interrupts needed by the 1000
and instructions for switching it to IRQ5 for IBM type machines were provided.
It quickly became apparent that the hard card as it came out of the box
wasn't going to fit in my particular machine. The Memory Plus card in the
left slot and the 286 Express card in the middle slot are both thick cards,
due to the piggybacked RS-232 card on the Memory Plus card and the
daughterboard in the same relative position on the 286 Express card. This
leaves virtually no clearance to the left of the right hand slot socket. If
the hard card's controller was inserted into the right hand socket its metal
backing plate would extend more than 1/4" to the left, encroaching into the
space needed by the 286 Express card's daughterboard. Furthermore, the drive
unit itself, on its 1" standoffs was going to be right against the card edge
connectors of the horizontally mounted 10 meg hard drive. As I saw it there
were three options: (a) return the drive to DCS and forget the whole thing;
(b) remove the controller and drive unit from the backing plate and mount them
separately (there's enough room to do that); or (c) rearrange the hard card's
mounting to pick up the needed clearances. Before making a decision I decided
to find out if the hard card was actually going to work in my setup.
First, the hard card's controller was removed from the backing plate and
installed in the right slot as a replacement for the original Tandy HD
controller. The rest of the hard card, consisting of the backing plate and
drive unit was laid on top of the power supply cover. The 10 megger's power
cable was unplugged and inserted into the socket on the "Y" cable which was
then plugged into the sockets on both hard drives. Because of the drive
select "twist" in the end connector of the 34 conductor cable it was clear
that DCS had set up the hard card to be drive C: and the old 10 megger to be
drive D:. That was my fault for not telling them I wanted it the other way
around. This was no problem as the hard card comes formatted as a bootable
drive with DOS 3.2 and COMMAND.COM installed. The 34 conductor cable was
plugged into the controller, its center connector to the 20 megger and the end
connector to the 10 megger. The two 20 conductor cables were run from their
separate connectors on the controller card to the corresponding card edge
connectors on the two drives. The computer was turned on and.....
Boot Disk Failure!
Hmm...the computer would boot from the floppy but wouldn't recognize
either one of the hard drives. Tried reversing the two 20 conductor cables
with the same result. After trying several other combinations of cable
connections with no success, I focused my attention on that drive select
"twist" in the wide cable. This method of drive selection had been used by
IBM so that all of its drives could use the same select jumper setting and the
actual drive number would be determined by its position on the daisy chain
cable. Having no better idea, I opened up that end connector and removed the
"twist" making it a straight-through cable. After plugging it back into the
10 meg drive, I applied power and was rewarded with a normal hard disk bootup,
with the 20 megger as C: and the 10 megger as D:. It wasn't the way I wanted
it but at least it worked. It turns out that the proper way to daisy chain
drives is to use a straight-through wide cable and use the drive select
switches or jumpers on each drive to determine the drive number. DCS had set
the jumper on the 20 megger for Drive 1 but why was the old 10 megger which
had been drive C: for all this time working so well now as D:? I found the
drive select block on the 10 megger right between the two card edge connectors
and discovered that it was jumpered as Drive 2! I can only guess that some
peculiarity of the Tandy HD controller connections had made this necessary.
Well, now it was easy to get things arranged the way I wanted them. I
jumpered the 10 megger as Drive 1, the 20 megger as Drive 2, reversed the two
20 conductor ribbon cables, turned on the computer and got a normal bootup
with the original 10 megger as C: and the new 20 megger as D:. Now, all I had
to do was find some way of squeezing the 20 megger into the computer....
I could have discarded that metal backing plate and mounted the drive unit
separately on a bracket I would have had to make. Instead, I elected to make
the whole hard card unit thinner. First, I mounted the controller card on the
plate using 1/8" spacers instead of the original 1/4" ones. Then, I remounted
the drive module on 1/4" spacers to replace the original 5/8" ones. That did
the trick. The hard card would now fit into the machine but just barely.
In fairness to DCS I should note that their hard card should fit easily
into a floppy-based 1000 with a normal thin card in the center slot. My
particular configuration was not one they had encountered before and they did
their best to provide what I needed. Had it not been for the helpfulness of
their technician, I could have ended up with a 30mb RLL drive with no way to
control my old 10mb MFM drive.
The new drive should be quite reliable, since it was designed to handle
RLL encoding and I understand that MFM encoding is a lot easier on a drive.
It certainly is extremely quiet. Once in a while I can hear the muted ticking
of its positioner if the room is very quiet, but that's about all.
Tom Price