HP 3000 III Series Manual page 342

HP 3242lA Series III Power Supplies
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CAUTION
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Do
not connect test equipment to power supply
chassis ground. All common circuits within
the power supply "float" with respect to
chassis ground. Damage to test equipment or
power supply components, and erroneous mea-
surements may result if this caution is
ignored.
9-13. Preventive Maintenance
The following preventive maintenance procedures are performed at
monthly or semi-monthly intervals. The frequency depends upon
the physical conditions prevailing at a particular site. Routine
maintenance once per month is adequate for most power supplies
that operate 24 hours per day, seven days per week. The interval
can be reduced in accordance with the amount of time the power
supply is turned off. The power supply is not removed from the
computer to perform preventive maintenance. Perform the preven-
tive maintenance procedures as follows:
a. Remove dust.
b. Check PCA's for proper seating.
c. Check cooling fan operation.
d. Check the dc operating voltages at the power supply front
panel.
e. Check the ac voltages for ripple at the PCA cage backplane.
To gain access to the power supplies, open the rear door of the
CPU cabinet bay. The power supplies are hinge-mounted and may be
swung-out by removing the screws that attach the left side of the
front panel to the CPU cabinet bay. In this position, the power
supply top and bottom covers can be removed for maintenance and
test.
If required, use a vacuum cleaner to remove dust and other light
debris from the power supply. Loosen encrusted dust with a soft-
bristled brush, paying particular attention to heat dissipating
areas. With the top cover of the power supply removed, check all
PCA's for proper seating. Adjust where necessary. Set the power
switch to ON and check the cooling fan for proper operation.
Ensure that no objects interfere with fan blade rotation.
Before making voltage checks, the voltmeter must be allowed time
to warm up as prescribed by the manufacturer of the instrument.
Also, the computer must run, with any type of program, for at
least 15 minutes before making the voltage measurement. Perform
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