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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.