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Operation
3.3
990/10A PWB INDICATORS
On the top edge of the 990/10A printed wiring board (PWB), there are additional LED indicators that
can be seen by looking into the chassis interior. Figure 3-3 shows an edge view of the 990/10A
board and the LED indicators. These indicators are explained in the following paragraphs.
3.3.1
Major Fault LED
The MAJFAULT
LED indicator is illuminated on power-up and extinguished after the kernel test
portion of self-test shows
that no major fault exists within the microprocessor-ROM
core of the
board. Unless the major fault logic itself fails, MAJFAULT
should always be illuminated when
power is initially applied to the board. If this LED fails to extinguish, the processor may have a
failure that prohibits displaying other error indicators.
3.3.2
FAULT LED
The
FAULT
LED
indicator is a duplicate
of the
FAULT
indication
on
the CDM.
It is software-
controlled to show a self-test, loader, or operating system fault.
3.3.3
Memory Error Indicators
The remaining LEDs on the 990/10A PWB provide the service person with indications of a failed
memory
component. This information is also available to software through the memory
error log
and will not generally require the user's attention.
3.3.3.1
Double-Bit
Error.
The
MER
LED
indicator designates
the occurrence
of a double-bit
memory error since the last reset to the memory error log. If the MER
LED is illuminated, all other
memory error indicators except the row-in-error information are unreliable.
3.3.3.2
Single-Bit
Error.
The
CER
LED
indicator designates
the occurrence
of a single-bit
memory error (correctable error) since the last reset to the memory error log. If the CER LED is illu-
minated,
but not the MER
LED, then the row-in-error and bit-in-error LEDs
pinpoint the memory
integrated circuit (IC) causing the error.
NOTE
The 990/10A 1M board does not have ROW or BIT-IN-ERROR LEDs.
2283234
Figure 3-3.
990/10A Board Failure Indicators
2302633-9701
Change 1
3-5
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