GEMini Atari/GEMini_Atari_CD-ROM_Walnut_Creek_December_1993.iso/zip/diskutil/diskdriv.lzh/DISKDRIV/SGL2DBL.TXT

Text File | 1988-10-26 | 10KB | 155 lines

               Single-sided to Double-sided ST Disk Upgrade
                            by Rod Smith (WAUG)

      Are you an ST owner with one single-sided and one double-sided disk
drive?  Annoying, isn't it, not being able to directly copy a file from one
double-sided disk to another.  Or do you perhaps have only single-sided
drives?  Wouldn't it be nice to halve the number of disks you've got by
making them double-sided?  Well you can!  The ST's disk drives are pretty
much industry-standard, although the connections to the ST are not.  This
means that, if you've got an SF354 single-sided drive, or an internal
single-sided drive, it's possible to replace it with a double-sided
mechanism for about half the cost of a new double-sided drive from Atari.
For 520ST-FM owners, in fact, this is the _only_ way to upgrade to a double-
sided drive, short of trading in your computer for a 1040ST.

_Some Caveats_
      This project, while not terribly complicated, is not for the faint of
heart.  It involves opening up your ST's drive (or your ST, in the case of
internal drives) and swapping components.  As such, it will void your
warranty, assuming it's not run out already.  I can make no guarantee that
it will work for you, especially if your system is different than mine or
you use a different drive than I did.  You may have trouble getting the new
mechanism to fit neatly in the old drive housing.  You will also likely be
out the cost of the replacement mechanism if something goes wrong.

_How I Did It_
      Bearing these caveats in mind, then, how is it done?  The procedure
I'm about to describe is how _I_ replaced _my_ SF354; the details will
likely be different for you, since my SF354 was very old (with an eject
button in the lower right-hand corner) and since you'll likely get a new
double-sided mechanism from a different source.
      My adventure began when I saw an ad for an external 3.5" drive from
Radio Shack on sale for $99.95 (catalog #25-1061).  This was a lower price
than I'd ever previously seen on such mechanisms, so I decided to go take a
look, and ended up buying one.  Other sources for 3.5" mechanisms can be
found in ads in electronics magazines and _Byte_.  One such source is Jade
Computer, in California.  Their phone number is [phone].  You could
also check with local computer stores; ask for a 3.5", double-sided drive
mechanism for an IBM PC.  A typical price seems to be about $120 for what's
generally a kit for mounting the drive in an IBM PC.  If you're replacing an
existing mechanism, you won't need a power supply, drive controller, or
extra mounting hardware, so don't pay extra for these things.  If possible,
buy a drive with an eject button and "disk busy" light which are in the same
location as they are in your existing drive.  This is especially important
if the drive does not include a case or if you're buying it to replace an
internal drive.  I'd avoid drives marketed for the Macintosh, since Mac
drives have been modified in strange and mysterious ways, and they're thus
more likely to give you troubles than more traditional drives.
      When I got my new drive home, I opened up both it and my SF354 (after
unplugging the drive from the wall, of course).  The SF354 has seven screws
on the bottom.  Remove the four outermost ones first; this will allow you to
remove the top cover of the drive.  The remaining three screws hold the
drive mechanism in place, and these should be removed as well.

_The Heart of the Beast_
      You now see the workings of your disk drive, as illustrated in the
figure.  There should be a small circuit board, with a pair of cables
leading to two connectors on the drive mechanism itself.  The larger cable
carries data signals to and from the drive, while the smaller feeds power to
the drive.  Your new mechanism should have similar connectors, and possibly
a circuit board of its own.  Disconnect both cables from your single-sided
mechanism and plug the cables into the new mechanism.  The cables may be
difficult to unplug.  I used a small flathead screwdriver to pry them apart.
_Be careful_ when doing this, though; snapping off one of the prongs could
cause serious problems.  When I did this, I actually moved the circuit board
from the SF354 to the Tandy drive, rather than swap the mechanisms, since
this was quick and I wanted to test the setup.  _This is something you
should do_.  When you've plugged the new mechanism into the SF354's circuit
board, you can test the drive.  Plug it in just as you would the SF354, and
turn on your system.  When I did this, I found that my new drive didn't
work!  After a few minutes of near-panic, I discovered the trouble.  The
Teac drive mechanism which Tandy used had a number of pairs of pins on the
top of the drive mechanism, some of which were covered by metal-and-plastic
caps, so as to make an electrical connection between the pins while
insulating them from other pairs of pins.  Some of these pins were labelled
"D0," "D1," "D2," and "D3," and a cap was placed on the pair labelled "D1."
Since I knew that every ST drive "thinks" it's the first drive, and since
these labels looked suspiciously like drive numbers, I used tweezers to move
the cap from "D1" to "D0."  I then re-connected the system, and everything
worked!  Other mechanisms may have a different means of selecting drive
number, so you may have to examine your drive carefully in search of such an
option, should it not work when you first connect it to your ST.

_All The King's Horses...._
      Now it's time to put everything back together.  Since the Tandy drive
I purchased had an eject button immediately below the center of the drive
slot, in a very different location than the placement of the button on my
SF354, and since the Tandy came with its own enclosure, I decided to leave
it that way.  I replaced the metal RF (radio-frequency) shielding and
discovered that the cables to the connectors (which necessarily sat rather
far within the housing, since the Tandy drive is deeper than an SF354) would
not fit through the only hole in the housing.  Fortunately, the top and
sides of the housing are plastic, so I merely cut out a corner in the back
large enough to admit my power cables.  It was then simply a matter of
putting the cover back on.  This setup has the disadvantage of an
inaccessible power switch and cable connectors.  Since I have a surge
protector/power strip, this isn't a real concern for me, but it might be for
somebody else.
      Those wishing to place a drive in an Atari housing will likely have to
remove the front pieces of the drive mechanisms and swap them.  This might
be difficult, since there's no guarantee that mounting screws will be
located in the same place (they aren't on my drives).  As mentioned before,
eject buttons and activity LEDs may be placed differently, as well.  It may
even be necessary to cut holes in the front of your Atari drive (or 520ST-FM
case!) to get everything to work.  Once you've worked through this problem,
you might have trouble mounting your drive in the SF354 case, since (as with
the faceplate) mounting screws are not guaranteed to match.  Once you've
worked around any of these problems which may arise, put the case back
together.
      One possible way to avoid these problems altogether might be to open
up your drive before even purchasing a replacement mechanism.  Find the
manufacturer's name and any other identifying marks, such as model or serial
numbers.  Then look specifically for the equivalent double-sided drive.
Since Atari has used several different makes of disk drive, there's no
guarantee that your neighbor's drive will be the same as yours, or even that
your two drives will be the same inside.  In other words, examine whatever
drive it is you're going to upgrade.
      If these problems prove nearly insurmountable, don't panic!  You could
nail together your own wood enclosure, or perhaps use something else, such
as a lunch pail or even (gasp) a "generic" external drive housing.  These
options are less viable for 520ST-FM owners, but they might still be
workable if you construct extension cables for your data and power lines.

_Some Speculation_
      If you want to buy a non-Atari drive as an _addition_ to your system,
rather than as a replacement for an existing drive, it may be possible, but
would require additional equipment.  Depending on the drive you get, you may
need an enclosure.  You'll also need a power supply and appropriate cabling
to reach the new drive.  Your situation in this case is basically the same
as connecting a standard 5.25" IBM drive to your ST.  I refer you to David
Small's article, "ST Uses IBM Disk Files," in the November, 1985 issue of
_Antic_ magazine for more details.  I'll add, though, that the additional
hardware purchases necessary for such a project will likely bring the total
cost to near what you'd pay for a new SF314, so it's probably not worth the
effort unless you already have some of the necessary components gathering
dust in a closet.

_All Done_
      With any luck, you've now got a functional double-sided drive where
you used to have a single-sided one.  So far, my new drive has read every
double-sided disk I've put into it, and my old double-sided drive has had no
trouble with disks formatted by the new one.  The new drive will format (and
read) to 83 tracks of 10 sectors each, so I have no difficulty using
extended formats.  I have encountered one problem, however: the new drive
seems to be less-than-diligent about reporting disk swaps to the ST;
sometimes it will report them, other times not.  This is not a major
problem, however, since certain actions, such as placing a write-protected
disk in the drive, will force correct behavior.  Other drives may or may not
have this problem.
      I certainly hope that anybody attempting this modification has as much
luck as I've had.  I've heard of it being done before, so I know that my
case isn't simply a lucky fluke.  I welcome any questions or comments.  Send
them to _MAM_ or post them on the Treasure CheST (973-9137), OutpoST (449-
8544), or Molin's Den (420-0407) BBS (all in the 313 area code).  Offers to
purchase a used single-sided mechanism are welcome.