Troubleshooting - HP 6236B Operating And Service Manual

current changes are to be achieved. Instead, a mercury-
wetted relay should be used for loading and unloading the
supply. Connect it in the load switching circuit shown in
Figure 5-5. When this load switch is connected to a 60 Hz
ac input, the mercury-wetted relay will open and close 60
times per second. The 25K control adjusts the duty cycle
of the load current switching to reduce jitter in the oscillo-
scope display. This relay may also be used with a 50 Hz ac
input.
5-31 Measurement Procedure. To measure the load
transient recovery time, follow the steps below for each
supply output. Transient recovery time may be measured at
any input line voltage and any output voltage within rating.
For this supply the specified load change is between half load
and full load.
a. Connect the test setup shown in Figure 5-5. Both
load resistors (R L ) are twice the normal value of a full load
resistance.
b. Turn on the supply and close the line switch on the
repetitive load switch.
c. Set the oscilloscope for internal sync and lock on
either the positive or negative load transient spike.
d. Set the vertical input of the oscilloscope for ac coup-
ling 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 then represents time zero.
f. Adjust the vertical centering of 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 transient
spike can be examined in detail.
Figure 5-6. Load Transient Recovery Time Waveforms
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
representing time zero, count to the right 50µs and
vertically 15mV. Recovery should be within these
tolerances, as illustrated in Figure 5-6.

5-32 TROUBLESHOOTING

5-33 Before attempting to troubleshoot this instrument,
ensure that the fault is in the instrument itself and not in
an associated piece of equipment. You can determine this
without removing the covers from the instrument by using
the appropriate portions of the performance test of
paragraph 5-6.
5-34 A good understanding of the principles of opera-
tion is a helpful aid in troubleshooting, and the reader is
advised to review Section IV of the manual before begin-
ning detailed troubleshooting. Once the principles of oper-
ation are understood, proceed to the initial troubleshooting
procedures in paragraph 5-35.
———
Before applying power to the supply, make
certain that its line voltage selector switch (S3)
is set for the line voltage to be used. (See
CAUTION notice in paragraph 3-2 for additional
information on S3.
5-35
Initial Troubleshooting Procedure
5-36 If a malfunction is found, follow the steps below:
a. Disconnect input power from the supply and
remove all loads from the output.
b. Table 5-2 lists the symptoms and probable
causes of several possible troubles. If the symptom is one
of those listed, make the recommended checks.
c. If none of the symptoms of Table 5-2 apply,
proceed to Table 5-3. This table provides an initial
troubleshooting procedure that also directs you to the
more detailed procedures which follow it.
5-37 The numbered test points referred to in the trouble-
shooting procedures are identified on the circuit schematic
and on the component location diagram at the rear of the
manual.
5-38 Open Fuse Troubleshooting
5-39
Although transients or fatigue can cause a fuse to
5-6
CAUTION ———
)