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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.