Technical data

Environmental Monitoring
6-13
6
Temperature Monitoring Function
The overtemperature LED on the front panel of the system indicates
the presence of excessive operating temperatures within one or
more of the following subassemblies:
❏ The power supply
❏ The card cage
❏ The standalone SCSI peripheral expansion enclosure (if
installed)
The SCSI enclosure also drives an overtemperature LED of its own
on the back panel.
Power Supply and Card Cage
Two temperature thresholds exist in a system power supply. In the
event of a heat buildup beyond the lower threshold within a
monitored power supply, thermal protection circuitry illuminates
the overtemperature LED on the front panel of the system.
Note If the SCSI peripheral expansion enclosure is the
location of the overtemperature condition, its
overtemperature LED also illuminates.
If temperatures climb further, beyond the higher threshold of
maximum safe ratings, an
ACFAIL signal is placed on the VMEbus
and the affected power supply is shut down automatically.
At the lower threshold, Motorola-supported devices and most
other devices in the system enclosure are approaching their upper
temperature limits but are not in danger of immediate damage.
In other parts of the system, temperature sensors provide only the
lower threshold warning. As with power supplies, a heat buildup
beyond the first threshold within a monitored subassembly
illuminates the warning LED on the front of the chassis. If
temperatures climb further, however, no power shutdown occurs.