TITLE
    SCSI Hard Disk Problem/Cure
Article ID:
Created:
Modified: 		3245
9/13/88
9/13/88
TOPIC

DISCUSSION



    PROBLEM:
    When an external SCSI hard disk is connected to either a Macintosh SE or
    Macintosh II with an internal SCSI hard disk, neither hard disk is recognized
    by the system. When the external drive is disconnected, the internal hard disk
    works correctly.

    Terms used in this article:
    UUT = unit under test

    CURE:
    1) Does the system with the internal drive come up ok by itself and
    do diagnostics pass ok?

    Yes -- Go on to Step 2
    No -- Repair machine with normal diagnostic techniques and then retest
    configuration

    2) Does the external SCSI device operate correctly on a Macintosh
    Plus, Macintosh SE with two 800Kb drives, or on the UUT when the
    internal SCSI cable is disconnected from the motherboard?

    Yes -- Go on to step 3
    No -- Repair external device using normal diagnostic techniques
    then re-test the configuration.

    3) a) Fix or replace the SCSI address select switch on the external SCSI
    device
    b) Fix or replace the SCSI Device select cable on the external SCSI
    device
    c) Check or replace the external device's SCSI terminator.

    Explanation: If the drives (internal and external) work independently of each
    other, chances are they conflict in one of two possible areas: Either there is
    a SCSI address conflict or the SCSI buss is not terminated properly.



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