From: tonyrich@titanic.cs.wisc.edu (Anthony Rich)
Newsgroups: comp.sys.mac.misc,comp.sys.mac.hardware
Subject: Re: Internal and External Hard Disks question
Summary: Here's how to do it, either way... (LONG)
Date: 30 Aug 92 02:52:38 GMT
Organization: University of Wisconsin, Eau Claire -- Computer Science Dept.

Jean-Michel Male writes:

> Is there a kind soul out there who could explain [...]  what is
> necessary to convert an internal hard disk to an external one ?

Below are instructions for converting an internal hard disk to an external
and vice versa, based on our experiences in doing so recently.  We removed
an external Fujitsu 520MB drive from its case and put it in a Quadra 700,
and we put the Quadra's internal 80MB drive in the external case.

DISCLAIMER:  I'm NOT responsible if you follow these instructions and
wreck your hard disk and/or computer.  The procedures below worked for me,
but I cannot guarantee that they will work for you.  Caveat swappor!

GENERAL WARNINGS:
You DO have to be careful.  If you are not technically inclined, have an
Apple-qualified technician do this for you so you don't ruin an expensive
hard drive and/or your Mac and/or void your warranties.

It's important to wear a grounding wrist strap so that you don't transmit
a static shock to any chips in the Mac or the HD as you work.  On modular
Macs, you should leave the Mac plugged into the wall (and turned OFF!), and
touch the metal power supply frequently to ground yourself to it.

That said, here's how we exchanged an internal 3.5" Quantum 80MB drive in a
Quadra 700 with an external 3.5" Fujitsu 520MB drive from MacDirect.
We thought it was going to be a 15-minute job, but it ended up taking quite
a bit longer because there we had to fiddle with termination, the
drive-activity LED's, and the SCSI ID switch.

In any external's case, you will (usually) find:

1.  The hard disk (HD).
2.  The power supply and fan, which you can ignore.
3.  A SCSI cable from the HD to the rear of the case.
4.  A power cable from the HD to the rear of the case.
5.  A 6-wire ribbon cable from the pins that select the SCSI ID number on the
    HD's circuit board to the SCSI ID switch at rear of the case.
    (Some external drives don't have a switch at the back for
    changing the SCSI ID number; ours did).
6.  A 2-wire cable from the HD to the "disk activity" LED at
    the front of the case.

In addition, our external HD had a 20-pin resistor chip for SCSI termination
taped onto the front of the hard drive inside the case, just in case anyone
ever wanted to add internal termination to the drive.  We appreciated that,
because we needed it!  (Thanks, MacDirect!)

NOTE: If you make an external drive an internal, it MUST be internally
terminated (if it wasn't already) -- otherwise, your Mac won't boot from it.


REMOVING THE INTERNAL HD FROM A MAC:

1.  Unplug the internal power cable from the HD.
2.  Unplug the internal SCSI data cable from the HD.
3.  Unplug the HD-activity LED (if there is one) from the HD.
4.  Unbolt the HD from its bracket (4 screws, usually).
5.  Gently lift the HD out of the Mac and set it aside.


REMOVING AN EXTERNAL HD FROM AN EXTERNAL CASE:

1.  Unplug the internal power cable from the HD.
2.  Unplug the internal SCSI data cable from the HD.
3.  Unplug the LED from the external case (not from the HD).

You can probably leave it attached to the HD if you intend to use the HD
as an internal drive.  (On a Quadra, the LED just gets placed into a
little plastic holder that transmits the light to the outside of the case.)
If there is already an LED for the internal drive in your Mac, check whether
its cable connector is compatible with the LED cable connector on the HD.
If so, you can just use the drive-activity LED that is already in your Mac.

4.  Unbolt the HD from its case (4 screws, usually).  You may also have to
remove a decorative plastic front panel from the front of the drive if it
has one -- on some drives, that panel acts as part of the front of the
external case, and you won't need it when the drive is used internally.

Our HD was mounted to the case with some spacers at each bolt position
that held the HD about 0.25 inch away from the HD case for ventilation.
We had to remove the spacers so the HD would fit into the Quadra properly.

5.  Unplug the cable to the SCSI ID switch from the HD.  It isn't needed on
the internal drive; if no cable is attached to the SCSI ID pins, the drive
will be SCSI 0, which is what the internal drive needs to be in order for
the Mac to boot from it.

NOTE:  If you want an internal drive to be something other than SCSI 0
because you already have ANOTHER internal boot drive that is already SCSI 0,
you will have to put some jumpers on the pins that the ID cable was attached
to.  The resulting SCSI ID will depend on which pins you connect together.
You'll need to consult the HD's manual to determine which pins to connect
to arrive at a specific ID number.


PUTTING THE OLD INTERNAL HD INTO THE EXTERNAL CASE:

About SCSI termination:

All Mac internal hard disks are terminated.  That usually means they have a
resistor pack installed somewhere on the HD circuit board that helps absorb
unwanted reflections at the Mac end of the SCSI bus.  But external SCSI devices
are not supposed to be terminated unless they are the *last* device on the
SCSI chain.  

So if you convert your internal drive an external drive, you probably
want to remove the termination resistor pack from it so that it is no
longer internally terminated.  You can buy a SCSI terminator that plugs into
the external port of the last SCSI device to terminate it if you need to.

The position of the SCSI terminator resistor pack on an internal drive
depends on the drive, so you'll need to contact the drive manufacturer
or find a manual for that drive to identify where it is, then extract it.
Be careful -- you certainly don't want to remove some other chip!  Once you
remove the terminator resistor chip, you might want to tape it somewhere
inside the external case (with its pins up) so that you can put it back in
the drive again someday if you want to.

On the other hand, if you plan to always plug the external drive at the end
of your Mac's SCSI chain anyway (for example, if it's your *only* external
SCSI device), you could just leave the termination resistor in it.

Assuming you've removed the terminator from the internal drive (or decided
to leave it in), putting the old internal drive into an external case goes
like this:

1.  Plug the case's HD-activity LED into the HD's connector for it, making
    sure the red and black wires are connected to the correct sides.
    If you get it backwards, nothing is harmed, but the LED won't light
    up when there's disk activity -- you'll have to open the case up
    again and flip the connector over.
2.  If the case has a SCSI ID selector switch, connect it to the SCSI ID
    selector pins (6 of them, in 2 rows of 3, usually) on the HD.
3.  Plug the SCSI data cable into the SCSI data connector inside the Mac.
4.  Plug the power cable into the power connector inside the Mac.
5.  Bolt the drive into the external case (4 screws).
6.  Bolt the cover onto the external case.


INSTALLING THE EXTERNAL HD AS AN INTERNAL DRIVE:

If you're installing a larger-than-normal drive into a Mac, you may need a
special bracket.  You can put 5.25" drives into Mac II, IIx, and IIfx models,
for example, but you need a special HD mounting bracket.  You can't put
5.25" drives into the other Mac models except the Quadra 900 and 950.

Assuming you already have a bracket or place to bolt the drive into your
Mac, the process goes like this:

1.  Plug the terminator resistor-pack chip into its socket on the HD's
    circuit board so that your new internal drive will be terminated.
2.  Plug the SCSI data cable into the SCSI data connector inside the Mac.
3.  Plug the power cable into the power connector inside the Mac.
4.  Plug the Mac's HD-activity LED into the HD's connector for it, making
    sure the red and black wires are connected to the correct sides.
    (If you get it backwards, you'll have to open the Mac up again
    and flip the connector over...!)
5.  Bolt the drive into the internal bracket on the Mac (4 screws).
    On our Quadra 700, we had to then snap the bracket with the HD mounted
    on it into the Quadra.

SURPRISES and SCREWUPS:

One surprise we had was that the LED indicator lights on the two drives
we were exchanging were different - one was a normal round LED bulb, but
the other was flat-shaped, and the connectors on their wires were slightly
different.  We had to cut the 2-wire cables between each LED and its connector
and then re-connect each LED to the other one's connector.

Also, I had forgotten that the external drive had a SCSI ID switch.  The
internal drive doesn't need a SCSI ID switch, since without one it acts
as SCSI 0.  But we had to locate which pins were the SCSI ID pins on the
old internal drive (and their order) so we could connect it to the switch
on the external's case.  Finding the pins wasn't hard, since we knew it
would be two rows of three unused pins.  But when we tested the drive,
we found out we put the connectors on wrong -- with the switch set to SCSI 2,
the drive was shown as SCSI 5 when we did Get Info on the drive icon.  So
we had to open the case again and put the two three-pin connectors back on
differently.  A diagram in the Fujitsu's drive manual showed the correct way.

Hope this helps.  Good luck to all!

  -- Tony
Newsgroups: comp.sys.mac,comp.sys.mac.misc,comp.sys.mac.apps