SA7x Technical Description
2.4 SA7x OCP and Transition Board Assembly
Note
The supply voltage to the fan does not change when the fan speed is
changed. Rather, the presence or absence of a control signal to the fan
produces the two-speed operation.
A fan rotation signal from the fan assembly is processed on TB2 and sent to the
power supply as ‘‘fan OK.’’ When the fan OK signal is lost, or when abnormal
ambient air temperature in the enclosure is detected, logic in the power supply
shuts down the enclosure.
Power and ground signals for each set of switches and indicators on the OCP
come from the associated disk drive through TB2. When a drive is not installed
in a disk drive position, the associated OCP is inactive and the corresponding
display is blank.
Asserting an OCP switch places an active low on its line to the disk drive; status
signals from the disk drive are active low to identify it as a state on a logic line.
SA7x Technical Description 2–7
