AT&T System 25 - Manual (Page 247)

MAINTENANCE
Fan Assembly Trouble
The fans should always be operating when the system is receiving ac power
and the cabinet switch is turned on. If the fans are not operating, be sure that
the system is receiving ac power.
if the system is receiving power and the fans are still not operating, the ac
power connection to the fan assembly is faulty or the fans themselves are
faulty (for example, burned out motors).
To check the ac power connection to the fan assembly, first unplug the
power cord, and then remove the four No. 6-32 screws at the corners of the
assembly. Carefully lift the fan assembly away from the cabinet. Check the
two modular plugs attached on the left side of the assembly. If the plugs are
securely attached, the fan assembly itself is faulty and must be replaced.
To replace the fan assembly, remove the modular plugs at the left side of the
assembly. Reconnect these plugs to a known good fan assembly, and
reinstall the new fan assembly by setting it in place in front of the power
supply and replacing the four No. 6-32 screws at the corners of the
assembly. (Without fans, the power supply will overheat and the system will
automatically shut down.)
Danger: Whenever the power supply shuts itself down (due to
overheating, shorting, etc.), unplug the power cord and
wait at least 5 minutes before restoring power.
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