Macintosh Portable: Connecting External SCSI Devices


I've had numerous problems connecting external SCSI devices to Macintosh
Portables. I've tried three Portables with several external SCSI drives
and printers.

When I tried to start up the Macintosh Portable with an external SCSI
drive attached, I received the question mark icon. After I disconnected
the SCSI system cable from the Portable, the internal hard immediately
kicked in and started up the machine.

Once the machine started up, I connected the drive and tried to mount it
with a SCSI CDEV utility. I was able to do so once, but in every other
instance, the utility was unable to identify the SCSI address of the
external drive or mount it. In fact, SCSI address 0 disappeared when the
external drive was connected, and nothing requiring internal hard disk
access could be done until the external drive was disconnected. This
corresponded with the symptoms while starting up; apparently the entire
SCSI bus was disrupted. However, SCSI address 7 remained intact.

Can you explain what's going on? Any ideas?

We have, on different occasions, connected numerous types of external hard
drives to the Macintosh Portable. In all cases, the drives and the
Macintosh Portable functioned properly.

Make sure you're using:

- Proper termination and good terminators

- Good cables

- The SCSI number on the peripheral is something other than 7
(reserved for the CPU) and 0 (if you have an internal hard disk).

- The external drive is not damaged. (If it is damaged, it may
not be providing proper termination power.)

- The external drive is connected and powered on before you
start up the Macintosh Portable.

We suspect that your problem may be caused by the last variable.

The Macintosh Portable does not provide termination power, so any external
SCSI devices connected to the Macintosh Portable must be turned on and
ready. Termination power is required for the terminator to terminate the
SCSI bus. Until external SCSI devices are powered on and ready, the
Macintosh Portable will not start up. The external SCSI devices must
remain on while using the Macintosh Portable, or the system will hang. If
you erroneously turn off an external device and the Macintosh Portable
hangs, you can sometimes resume by turning the SCSI device back on.

The proper and safest way to add SCSI devices to the Macintosh Portable
is to first turn off the Macintosh Portable using the Shut Down function.
Also make sure the external SCSI devices are turned off. Your external
SCSI devices can then be plugged in without damaging the Macintosh
Portable.


Published Date: Feb 18, 2012