Troubleshooting; Repair - HP 4262A Operating And Service Manual

Section VIII
Paragraphs 8-42 to 8-44
8-42. TROUBLESHOOTING.
CAUTION
THE OPENING OF COVERS OR
THE REMOVAL OF PARTS, EX-
CEPT THOSE TO WHICH ACCESS
CAN BE GAINED BY HAND, IS
LIKELY TO EXPOSE LIVE
PARTS. IN ADDITION, ACCES-
SIBLE TERMINALS MAY ALSO
BE LIVE.
THE APPARATUS SHALL BE
DISCONNECTED FROM ALL
VOLTAGE SOURCES BEFORE
ANY ADJUSTMENT, PARTS
REPLACEMENT, OR MAIN-
TENANCE AND REPAIR ARE
PERFORMED FOR WHICH THE
INSTRUMENT MUST BE OPEN-
ED. IF, AFTERWARDS, ANY
ADJUSTMENT, MAINTENANCE
OR REPAIR OF THE OPENED
INSTRUMENT UNDER VOLT-
AGE IS REQUIRED, IT SHALL
BE CARRIED OUT ONLY BY A
SKILLED PERSON WHO IS
AWARE OF THE HAZARD IN-
VOLVED.
8-43. When 4262A is inoperative or readings for
the sample connected to the UNKNOWN terminals
are incorrect, you should first check power line
voltage used and next the behavior of instrument
with respect to the DUT when a measurement is
attempted. The two may be incompatible. In
addition, check for appropriate test leads or
fixture. Determining whether the trouble is in an
external device connected to the instrument or is
in the actual instrument is primary and a funda-
mental procedure which must precede trouble-
shooting the LCR Meter. Occasionally, the un-
known sample may have characteristics not
measurable by the 4262A. Table 8-2 lists the
examples of symptoms likely to mislead. You
should also be concerned about the operating
environmental conditions in which the instrument
is operated. Surrounding magnetic fields or the
presence of a strong radiowave will sometimes
disturb the measurement. To isolate any instru-
ment trouble from the above possibilities, perform
the following examinations:
1) Measure a sample whose characteristics and
value (L, C or R and D/Q value) are known
to be measurable with the 4262A. Thus, if
the problem is restricted to difficulty in
measuring a particular sample, it might
suggest that the sample is not measurable
with the 4262A.
8-16
Model 4262A
2) Next, connect sample directly to the UN-
KNOWN terminals without using any test
fixture or test leads. Any external equip-
ment being used with 4262A should be
disconnected from the connectors of the
4262A. These tests isolate troubles on the
external equipment or test jig from those on
the instrument.
3) Securely ground the instrument to earth. If
environmental conditions are suspected,
change the location of instrument.
4) Use a four terminal connection configura-
tion and measure a sample. An improper
connection to unknown will cause a meas-
urement error.
5) Properly terminate UNKNOWN terminals
(short or open circuit), and press SELF
TEST button. Confirm that normal PASS
annunciator readouts occur on the LCR
DISPLAY.
8-44. Figure 8-10, "How to Use Troubleshooting
Guides", is helpful when starting to troubleshoot
the 4262A. This flow diagram shows the funda-
mental procedures which breakdown the trouble
possiblilities to the component level. The trouble-
shooting guides are divided into the following
major procedures:
Power Supply Section Isolation Procedure
(Fig. 8-17).
Basically used for checking internal dc power
supply voltages of the instrument: The guide for
checking the power supply section is included in
Figure 8-17.
Option Section Isolation Procedure (Fig. 8-17).
This procedure, which is used to isolate the option
section from the overall unit, is included in Figure
8-117. If the instrument is a standard unit equipped
with no option, omit this procedure.
Analog and Digital Section Isolation Procedure
(Fig. 8-17).
The troubleshooting guide in Figure 8-17 describes
how to distinguish whether the faulty assembly is
located in the analog or in the digital section. In
conjunction with the troubleshooting flow diagram
of Figure 8-17, the built-in self test function is
used to assist in isolating the analog section from
the digital section. To study the self test function,
refer to Figure 8-11. - '