How to hook up another logical drive to your SH204 without another con -
troller
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by John White
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Warning: While opening up your SH204 doesn't void your warrenty, this does
DON'T do it unless you know what you're doing.
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Now, on to the good stuff!
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Required Tools: Phillips screwdriver
                Soldering Iron 
                Ribbon Cable Connector Crimper
                Needle nose pliers  
                Wire cutterstripper 
  
 Materials:     Hard Disk drive (media only) 
                10-20" 34 conductor ribbon cable   
                10-20" 20 conductor ribbon cable   
                34 position card edge connector    
                20 position card edge connector    
                20 position dual header connector  
                4 pin power connector and cable    
                Electronic solder   
                Supra's hard disk software  
  
I used another Seagate ST-225 (20Mb), but I think this can be done with o-
ther similar drives, like the 30Mb ST-238, maybe even with a miniscribe
drive, but don't count on it.

Nobody else's lets you set the logical drive number.  
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 At this point, it's probably a good idea to backup your entire hard disk
drive. Hooking up another drive shouldn't distroy what's on your first one
but...
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Park your heads too, just in case...
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Disconnect the drive from the ST and the power cord. Remove all 8 screws
from the sides of the  SH204, and pull the case straight up, but not too
far, the LED is attached to the front of it. There is a 50-pin cable con -
necting the DMA interface to the controller which you must unplug. Pull it
STRAIGHT UP or you will bend the pins. Now remove the four nuts, the card-
board insulator and the four plastic washers that are attached to the con-
troller. Carefully lift the controller free of it's four mounting bolts
and disconnect the power cable and the two drive cables. Now you can get
that nasty cover out of your way.

Now, unplug the power cord and the 34 pin cable (the bigger one) from the
drive.
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Making the cables... 
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Take apart the 34 pin cable by prying the sides out of the connectors
(both of them) and pulling off the back. Be careful, if you break them,
then you'll have to buy new ones.

First, make a longer version of this cable, ie. looks the same, only lon -
ger. Now, about 2.5-3" from one end, connect your new 34 pin connector to
the cable facing the same way as the others, and that's one cable. The o -
ther one is easier, if you bought new parts. Connect the 20-pin card edge
connector to one end of the 20 conductor cable, and the 20 pin header con-
nector to the other end. That's two. Number three is a power cable, and
you're gonna have to get out the soldering iron. You need to connect the
new power cables the same way the existing ones are connected.

I found it easiest to pull the pins out of one of the existing ones and
solder the new one's wires to it. This avoids soldering directly to the
power board or cutting the wires. Just make sure you get the polarity
right...hook it up so it plugs in with the same wires in the same orienta-
tion. If you do this wrong you can kiss your SH204 and your new hard disk
goodbye.   
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Hooking it up...
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On the controller board you will see two 20-pin headers side by side. The
one on the outside is for drive 0, the one on the inside is for drive 1.
Plug the new 20 pin cable into the inside one (drive 1). There is another
20-pin connector in the middle of the controller board - ignore it. Plug
the end of the 34 pin cable that has another connector close to it into
the existing drive and the controller board, and the short 20-pin cable
into the drive and the outside 20-pin header on the board. Make sure there
are no twists in either cable. Connect the power cables to the drive and
the board (they only fit one way). Re-mount the controller board, and plug
the 50-pin cable back into the DMA interface.

On the back of your new drive (at least if it's a Seagate) there is a 20-
-pin header like the ones on the controller board. There should be a jum -
per across the two pins on the left hand side (from the back). Use the
needle-nose pliers to move this jumper one position to the right. This is
the drive select jumper. Now, hook up the 34-pin, 20-pin and power cables
so that when you place the new drive on top of the controller, and facing
forward, there are no twists in the cable. Hook the SH204 up to the compu-
ter and plug it in.  
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Booting it...   
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Turn on the SH204. The lights on both drives should come on and you should
hear them comimg up to speed. If you do not see this, turn the drive off,
you have hooked up something wrong, and you had better hope it wasn't the
power cable. Both drives should boot, but one may take longer than the o -
ther. Wait until both drives are up to speed and all lights are off before
you turn the computer on. When you boot your system, do it with the Supra
software and watch the drives while it is booting. Both drive lights
should flash. If they don't, check for a twisted cable and check the drive
select jumper on your new drive.
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Up and running...
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Run SUPFMT.PRG. Click on DRIVE NUMBER and set the LOGICAL UNIT NUMBER (not
the SCSI number) to 1. Click on OK and the program should say hello to the
new drive. If it already has an Atari ST format you won't need to re-for -
mat it, it's partitions should be good. Otherwise, set the drive type to
whatever type your drive is and format the drive. If you have problems at
this point, like the drive won't format, you may have to hook the new dri-
ve up as logical unit 0 (in place of the old drive) and format it.  I had
to do this because the old format on my new drive was not Atari ST format,
and for whatever reason, the Supra software couldn't format it. I even -
tually had to use HDX, then hook up the drive as unit 1, after which it
worked fine. Maybe this was because I mucked up the drives format before I
had it hooked up right.
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One more problem...
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For some reason, SUPBOOT makes all drives from C-P available, whether they
are valid partitions or not. This makes it extremely difficult to use a
Ramdisk. I had to modify my custom configuration program to shut off the
invalid drives by changing the system variable DRVBITS (at $4C2-4C5). Af -
ter this it worked fine, and I now have 40Mb.
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 Some advice...
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Build a new box for your drives, one with a fan in it so that your drives
don't overheat. They are very prone to this, since they need adequit ven -
tilation. And don't make the cables too long, the drive's peak data trans-
fer rate is 5 megabits per second.
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If you have any trouble you can call me in Ottawa after 6 at (613)
825-1499, or leave me a message on the Atari Access BBS in Toronto.
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John White
July 28, 1987
Oop Ack!
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P.S.  Please excuse my spelling and my grammar.
      I used to use a Mac and am now a little warped.
