Status Leds; Power Diagrams - HP 9020 Service Manual

2-8 Theory of Operation
The start-up/shutdown sequence control circuitry is controlled by a 30-kHz clock. The signals
generated by this circuitry are defined as follows:
PPON - Primary Power On; all outputs in specification.
NPV - Not Power Valid; this signal is the inverse of PPON, and therefore signifies "not
all outputs in specification".
NPI - Not Pop In; used to reset the processor stack.
NSYSPU - Not System Pop Unsynchronized; used with NPI to cause the processor stack to
perform a self-test.
Status LEOs
Fifteen LEOs are contained in the power supply assembly to provide fault status indications. All
LEOs are contained on the supervisor board. Specific reasons for power supply assembly failures
are indicated by the LEOs.
Two LEOs are visible from the rear of the computer through the power supply assembly fan. The
green LED is tied to the
+
16V bias supply. When lit, the green LED indicates that power is applied
to the assembly and bias voltage is available from the primary board. The yellow LED indicates that
no failures have been detected. It also indicates that the supervisor board is enabled and capable of
detecting faults and shutting down the power supply assembly if a failure is detected.
The other LEOs are visible at the top of the power supply assembly with the front cover removed.
They are labeled on the assembly and defined as follows:
DOORS OPEN - indicates that 110 card cage door or processor stack door is open. OV also
lights.
STACK TEMP - indicates that processor stack temperature has exceeded 100
o
e.
SEC BOARD - indicates that
+
12MM mass storage power supply has failed or that tempera-
ture in power supply assembly has exceeded 97°e.
PWR - indicates that peak primary current exceeded 9A.
OV - used in conjunction with voltage LEOs described below; "on" indicates an
overvoltage condition on one or more of the supplies or door open, "off"
indicates ar. undervoltage condition.
- 19 - indicates a fault condition on the applicable supply. If the OV LED is also lit,
- 12
an overvoltage condition is indicated. If the OV LED is not lit, an undervol-
- 2 tage condition is indicated.
3
5
6
12
19
Power Diagrams
Figures 2-4, 2-5, and 2-6 illustrate power distribution, voltage sensing, and safety grounding,
respectively.
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