2-12
Theory
of
Operation
Power Interlock Switch
A power interlock microswitch causes power supply shutdown if the stack door
is
opened
with
power on. Shutdown results
in
all
RAM
data being lost. The power switch must
be
cycled to power
up the computer. The power interlock switch prevents damage to boards caused by their removal
or insertion with power on,
and
prevents a shock hazard to personnel.
Cooling
A dc box fan
is
mounted at
one
end
of the stack to draw cooling air through the stack. An air
controller
is
mounted
in
the stack. The air controller blocks air from circulating through the
open
area if the stack
is
not
filled
with boards and ensures that most of the cooling air
is
circulated
between the boards.
The fan has three speeds that are varied according to the temperature sensed
on
the secondary
board heat sink
in
the power supply assembly. Refer to the preceding Power Supply Assembly
description for details
on
fan speeds and temperature thresholds.
Memory
This subsection describes the organization of
RAM
memory within the stack. It also describes error
detection
and
correction, mapping,
and
healing.
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