HP 7957A Hardware Manual page 93

4-65.
Service Information
7957 A/7958A
This utility will read the firmware ROM revision numbers and return them in an
execution message. The first byte specifies the number of revision number bytes
that will follow.
byte #
o
number of bytes to follow
(equals 1 since there is only one ROM)
revision # for ROM
The format for the revision byte is for the most significant nibble to
contain the main revision number, and for the least significant nibble to
contain a secondary revision number.
Troubleshooting
When troubleshooting the disc drive, the first thing to do is to determine if the
fault is repeatable or intermittent. A repeatable fault usually causes the same
self-test fail result to be presented each time self test is performed. An
intermittent fault, on the other hand, occurs at random intervals, and may not
always cause a self-test failure.
In the case of a repeatable fault, self test will identify the failing FRA with a 95
percent certainty. In the event that more than one FRA is lsi ted as the possible
cause of the failure, replace the FRA's one at a time, in the order given in the
self-test display.
NOTE
Cable faults (an open cable conductor, loose cable connector, etc.)
may present a multiple FRA failure message. The FRA's listed will
be the FRA's at either end of the defective cable. All cabling should
therefore be checked before replacing any FRA's.
Cables W I and W3 are sufficiently long to allow PCA-AI (disc
drive assembly AI) to be connected into the circuit adjacent to the
disc drive cabinet. This allows a substitute PCA-A I to be connected
into the circuit without removing PCA-AI from the cabinet.
Attempt to isolate the fault to a specific FRA by running self test
following the replacement of each FRA.
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