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    AST RESEARCH, INC.        TECHNICAL BULLETIN # 1135                4-10-95

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    			   BRAVO LC 4/50S HANGS WITH ADAPTEC 1522 SCSI

    PROBLEM

    When using an Adaptec 1522 SCSI controller in the Bravo LC 4/50S system,
    accessing an attached SCSI CD-ROM may cause the system to hang.

    CAUSE

    The Bravo LC 4/50s system may hang because the Adaptec 1522 SCSI controller
    has excessive noise on its interrupt lines.  The noise is occasionally
    interpreted as an actual interrupt by the Bravo system, leading to a system
    hang.  The failure is only observed when the Adaptec 1522 SCSI controller is
    set for IRQ 10 or 11.  This problem does not occur on IRQ 12 because the
    routing of that line to the mouse port adds sufficient impedance to dampen
    the glitch, preventing it from being interpreted as a valid interrupt.

    SYSTEMS AFFECTED
    AST PART NUMBER AND DESCRIPTION

    501433-010     BRAVO LC 4-50S/273W 8MB

    SOLUTION

    Adaptec has modified their 151x/152x series adapters to filter out the noise
    on the interrupt line. These boards can be identified by the following part
    numbers and revisions:

    Product Name             Part Number    Old Revision        New Revision

    AHA-1510A Host Adapter   555700         A                   B
    AHA-1520A Host Adapter   555000         B                   C
    AHA-1522A Host Adapter   555300         B                   C
    AHA-1522A Kit            569900         AA                  A1

    The part number and revision level can be observed on a paper label which is
    located on the component side of the board.  Customers with this problem
    should be referred to Adaptec Inc. at (800) 959-7274 and ask about Adaptec
    Service Advisory #6786A.