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SECTION V
MAINTENANCE
5-1
INTRODUCTION
5-2
Upon receipt of the power supply, the per
formance check (Paragraph 5-13) should be made.
This check is suitable for incoming inspection. If
a fault is detected in the power supply while
making the performance check or during normal op
eration, proceed to the troubleshooting procedures
(Paragraph 5-46). After troubleshooting and repair
(Paragraph 5-53), perform any necessary adjust
ments and calibrations (Paragraph 5-55). Before
returning the power supply to normal operation,
repeat the performance check to ensure that the
fault has been properly corrected and that no other
faults exist. Before doing any maintenance checks,
turn-on power supply, allow a half-hour warm-up,
and read the general information regarding measure
ment techniques (Paragraph 5-6).
5-3
COVER REMOVAL AND REPLACEMENT
5-4
To remove the top and bottom covers, pro
ceed as follows:
a.
Insert a small screwdriver in each of the
four notches at the front of the unit at the top and
bottom. Push the screwdriver under the front panel
and gently pry toward the front of the unit to re
lease the holding mechanism.
b.
Pull the front panel forward until it clears
the top and bottom covers.
c. Remove the rear cover by repeating step a.
d. Pull the rear cover until it clears the top
and bottom covers. Then lift off the top cover and
lift the unit out of the bottom cover.
5-5
To replace the top and bottom covers, pro
ceed as follows:
a.
Place the unit into the bottom cover
(identified by the four protruding feet) and align
the heat sink into the track in the bottom cover.
b.
Place the top cover over the unit and
align the track over the heat sink.
c. While holding the covers together at the
rear of the unit, carefully push on the rear panel.
d.
Position the front panel so that the two
slotted ears at the bottom of the panel align with
the printed wiring boards.
e.
Carefully push on the front panel.
5-6
GENERAL MEASUREMENT TECHNIQUES
5-7
The measuring device must be connected as
close to the output terminals as possible when
measuring the output impedance, transient re
sponse, regulation, or ripple of the power supply
in order to achieve valid measurements. A meas
urement made across the load includes the imped
ance of the leads to the load and such lead lengths
can easily have an impedance several orders of
magnitude greater than the supply impedance, thus
invalidating the measurement.
5-8
The monitoring device should be connected
as shown in Figure 5-1.
Note that when measure
ments are made at the front terminals, the monitor
ing leads are connected at A, not B, as shown in
Figure 5-1. Failure to connect the measuring de
vice at A will result in a measurement that includes
the resistance of the leads between the output
terminals and the point of connection.
OUTPUT TERMINAL-
LOAD LEAD
MONITOR HERE-
Figure 5-1.
Front Panel Terminal Connections
5-9
For output current measurements, the current
sampling resistor should be a four-terminal resis
tor.
The four terminals are connected as shown in
Figure 5-2. In addition, the resistor should be of
the low noise, low temperature coefficient (less
than 30 ppm/°C) type and should be used at no
more than 5% of its rated power so that its temper
ature rise will be minimized.
CURRENT SAMPLING
TERMINALS
EXTERNAL
TO UNGROUNDED
TERMINALOF
POWER SUPPLY
SAMPLING
RESISTOR \
LOAD
TERMINALS
TO GROUNDED
TERMINALOF
\ POWER SUPPLY
Figure 5-2. Output Current Measurement Technique
5-10 When using an oscilloscope, ground one ter
minal of the power supply and then ground the case
5-1
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Troubleshooting
