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    AST RESEARCH, INC.         TECHNICAL BULLETIN # 1253                7-18-95

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    EISA CMOS ERRORS WHEN EISA ADAPTERS ARE ADDED AND THE SYSTEM IS POWERED ON

    PROBLEM

    When the Premmia GX is powered on after adding an EISA adapter to the system,
    the EISA CMOS becomes corrupted causing the following two POST text messages
    to be displayed:

    16.01 EISA CMOS checksum error - run EISA Configuration Utility.

    16.10 The computer has a memory problem.  Run the EISA Configuration Utility
    to check the memory corruption.

    CAUSE

    Fault analysis reveals that the failure is caused by an anomalous write into the
    8kx8 ECOMS SRAM (at location U51).  The write occurs shortly after power on
    (about 200ms before POWERGOOD is asserted).  TTL and CMOS gates on the
    motherboard drive the SRAM's WE* and CE1* inputs.
    As Vcc is ramping to 5v, these gates (at Vcc~=2.5v) generate transients
    which cause the simultaneous assertion of WE* and CE1* at the SRAM;
    hence a write of whatever value happens to be on the data bus (usually 00h)
    to whatever address is being presented to the SRAM.

    SYSTEMS AFFECTED
    AST PART NUMBER AND DESCRIPTION

    501457-XXX      PREMMIA GX P/90
    501522-XXX      PREMMIA GX P/100

    SOLUTION

    The following motherboard rework will remove this spurious write from the
    system.

    1) Disconnect BPRWGOOD from the gate of Q3 by cutting the etch to the
    gate pad (cut it at the pad on the component side of the motherboard).

    2) Connect PWRGOOD to the gate by adding a wire (on the component side)
    from location U69-1 to the gate of Q3.

    The resolution for the field is to replace the motherboard (P/N 202604-XXX)
    with the above fix implemented as detailed in ECN AE55.

    CAUTION

    This modification should be performed ONLY by a qualified service technician.
    It is strongly recommended that this change be completed by an AST Authorized
    Service Center.  In no case will AST Research, Inc. be liable for damage to
    the system and its components, or loss of data caused by improper
    modification.

    PREREQUISITES

    A full backup of all data on the hard drive in the computer is strongly
    suggested.

    TIME REQUIRED

    30 minutes.

    STATUS VERIFICATION

    The revision level of the AST riser card can be identified by observing the
    revision letter at the end of the nine-digit part number located on the solder
    side of the card.

    TOOLS REQUIRED

    Standard computer tools.

    INSTALLATION PROCEDURE

    Refer to the system Hardware Maintenance Manual.

    Removal and replacement of system "Field Replaceable Units" (FRUs)
    should only be performed according to the installation procedures approved
    and prescribed by AST Research, Inc.

    Remove the riser card according to procedures approved and prescribed by
    AST Research, Inc.

    CHECK-OUT PROCEDURE

    To verify proper operation of the system upon completion of this change,
    follow the setup and test procedures described in the AST User's Manual.

    NOTE

    Warranty reimbursement for this change requires prior AST Research, Inc.
    approval.

    The warranty on this system will become VOID if this change is completed
    by ANYONE other than an AST Authorized Service Center.