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Figure 5-7. Constant-Current Load Regulation Test Setup
POWER SUPPLY CASE
OSCILLOSCOPE CASE
A. INACCURATE
METHOD
USING
SINGLE
ENDED
SCOPE.
GROUND
CURRENT
IG
PRODUCES
60 CYCLE
DROP
IN
NEGATIVE
LEAD
WHICH
ADDS
TO
THE
POWER
SUPPLY
RIPPLE
DISPLAYED
ON
SCOPE
POWER SUPPLY CASE
OSCILLOSCOPE CASE
*
LENGTH
OF L E AO
BETWEEN
Rs
AND GROUNDED OUTPUT
TERMINAL of
POWER
SUPPLY
MUST BE HELD
TO
ABSOLUTE
MINIMUM
B. RECOMMENDED METHOD USING A DIFEERENTIAL
SCOPE
WITH
FLOATING
INPUT.
GROUND CURRENT
PATH
IS
BROKEN, COMMON
MODE REJECTION
OF
DIFFERENTIAL
INPUT
SCOPE
IGNORES
DIFFERENCE
IN GROUND
POTENTIAL OF
POWER
SUPPLY
AND
SCOPE, AND SHIELDED
TWO-WIRE
FURTHER
REDUCES
STRAY
PICKUP
ON
SCOPE
LEADS.
Figure 5-8. Constant-Current Ripple and Noise Test Setup
supply. The presence of a 1 20Hz waveform on the oscillo¬
scope normally indicates a correct measurement method.
A waveshape having 60Hz as its fundamental component
usually indicates an incorrect measurement setup.
5-48
To check the ripple and noise, proceed as follows:
a. Connect oscilloscope or rms voltmeter as shown in
Figure 5-8A or 5-8B.
b. Rotate VOLTAGE controls fully clockwise.
c. Turn on supply and adjust CURRENT controls until
front panel ammeter reads exactly maximum rated output
current.
d. The observed ripple and noise should be less than:
6259B
250jljV rms
6260B
250/uV rms
6261B
250/iVrms
6268B
334/jV rms
6269B
250juV rms
549
TROUBLESHOOTING
5-50
Before attempting to troubleshoot this instrument,
ensure that the fault is with the instrument and not with
an associated circuit. The performance test (paragraphs
5-5 through 5-48) enables this to be determined without
removing the instrument from the cabinet.
5-51
A good understanding of the principles
of opera¬
tion is a helpful aid in troubleshooting, and it is recom¬
mended 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
overall troubleshooting procedures in paragraph 5-54 to
locate the symptom and probable cause.
5-52
The schematic diagram contains normal voltage
readings adjacent to some test points. (Test points are
identified by circled numbers.) The measurement conditions
are listed in the Schematic Notes. Consult the component
location diagrams in Section VII to determine the locations
of components and test points.
5-53
If a component is found to be defective, replace
it and re-conduct the performance test. When a component
is replaced, refer to the repair and replacement (paragraph
5-69) and adjustment and calibration (paragraph 5- 71)
sections of this manual.
5-54
OVERALL TROUBLESHOOTING
PROCEDURES
5-55
To locate the cause of trouble, follow steps 1, 2,
and 3 in sequence:
(1)
Check for obvious troubles such as a defective
power cord, an input power failure, or a defective meter.
5-8
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