HP A Series User Manual

5-36 To check the transient recovery time, proceed as
follows:
a. Connect test setup shown in Figure 5-4. Both
load resistors (Rj) are twice normal value of full load
resistance.
b. Turn on supply and close the line switch on
the repetitive load switch setup.
c. Set the oscilloscope for interna! sync and lock
on either the positive or negative load transient spike.
d. Set the vertical input of the oscilloscope for
ac coupling so that small dc level changes in the output
voltage of the power supply will not cause the display
to shift.
e. Adjust the horizontal positioning control so
that the trace starts at a point coincident with a major
graticule division. This point is then representative of
time zero.
f. Adjust the vertical centering on the scope so
that the tail ends of the no load and full load waveforms
are symmetrically displaced about the horizontal center
line of the oscilloscope. This center line now represents
the nominal output voltage defined in the specification.
g. increase the sweep rate so that a single tran¬
sient spike can be examined in detail.
h. Adjust the sync controls separately for the
positive and negative going transients so that not only
the recovery waveshape but also as much as possible of
the rise time of the transient is displayed.
i. Starting from the major graticule division rep¬
resentative of time zero, count to the right BOjUsec
and vertically 15mV. Recovery should be within these
tolerances: as illustrated in Figure 5-5.
Figure 5-5. Transient Recovery Time Waveforms
5-37 TROUBLESHOOTING
5-38 Before attempting to troubleshoot this instru¬
ment, ensure that the fault is with the instrument
itself and not with an associated circuit. The perfor¬
mance test enables this to be determined without
having to remove the covers from the supply.
5-39 A good understanding of the principles of
operation is a helpful aid in troubleshooting, and it is
recommended that the reader review Section IV of the
manual before attempting to troubleshoot the unit in
detail. Once the principles of operation are understood,
refer to the initial troubleshooting procedures in Para¬
graph 5-41 to locate the symptom and probable cause.
5-40 Various lettered test points are located at
critical points on the PC board to assist in trouble¬
shooting. These test points are also included on the
schematic diagrams at the rear of the manual.
5-41 Initm! Troubleshooting Procedures
5-42 If a malfunction occurs, proceed as follows:
(1} Disconnect input power and remove all loads
from unit.
(2) Ensure that +S and —S terminals are strapped
securely to proper output terminals.
(3) Measure output voltage across sensing ter¬
minals and proceed to Table 5-2 to locate your symptom
and appropriate isolation procedures.
5-43 Open Fuse Troubleshooting
5-44 Although an open line fuse can be caused by
fatigue or line transients, it is recommended that the
unit be first checked for internal shorts before replac¬
ing the fuse. To accomplish this test, follow the below
steps in sequence:
(1) Visually inspect the unit for charred compo¬
nents, foreign matter, and obvious shorts.
(2) With power removed, connect an ohmmeter
between + output terminal and test point F on the
P.C. board. Reading should not be less than the value
of R31 (between 200 and 5,600 ohms, depending upon
the model number) after filter capacitor C9 becomes
charged. If resistance is less than R31, check C9, CR3,
4, 5, 6, (or U4), Q4, (Q5), CR8 (or U5), CR9 (or U5)
or Cl 1 for short
(3) Connect ohmmeter across reference supply
filter capacitor (test points B and N). Reading should
5-6

HP A Series Specifications

General

Brand	HP
Model	A Series
Category	Power Supply
Language	English