HP 3478A Technical Manual page 79

TM 11-6625-3071-14 TM 11-6625-3071-14
7-B-1. INTRODUCTION 7-B-1. INTRODUCTION
7-B-2. This Service 7-B-2. This Service Group has Group has the AC
Current troubleshooting information for the 3478A and is Current troubleshooting information for the 3478A and is
symptoms symptoms oriented oriented
troubleshooting for AC Volts or AC Current Failures, troubleshooting for AC Volts or AC Current Failures,
make sure the 3478A's DC Volts and DC Current make sure the 3478A's DC Volts and DC Current
Functions are operating correctly (go to Service Group A, Functions are operating correctly (go to Service Group A,
if the functions if the functions fail). fail).
before the AC Volts and AC Current Functions can before the AC Volts and AC Current Functions can
operate. operate.
The instrument contains CMOS Integrated The instrument contains CMOS Integrated
Circuits Circuits (e.g. (e.g. U102) U102) which
susceptible susceptible to to
discharge. discharge. It It is is especially
grounded tools and wrist straps be used grounded tools and wrist straps be used
when handling or troubleshooting these when handling or troubleshooting these
components. components.
7-B-3. 7-B-3. AC AC VOLTS VOLTS TROUBLESHOOTING TROUBLESHOOTING
7-B-4. 7-B-4. An AC Volts Fa An AC Volts Failure can be Overloa ilure can be Overload, Inaccurate,
Floating, or Noisy Readings Floating, or Noisy Readings on all or so
following following paragraphs paragraphs
troubleshooting procedures (go to troubleshooting procedures (go to paragraph 7-31
description description of of these these failures).
specified, specified, refer refer to to Schematic Schematic 2 2 for
troubleshooting procedures. troubleshooting procedures.
7-B-5. 7-B-5. Overload, Floating, Overload, Floating, or Noisy
Ranges Ranges
7-B-6. An overload 7-B-6. An overload reading can be reading can be caused if one of
amplifiers or the RMS Converter in the AC to DC Con- amplifiers or the RMS Converter in the AC to DC Con-
AC VOLTS AND AC CURRENT TROUBLESHOOTING AC VOLTS AND AC CURRENT TROUBLESHOOTING
T T i i t t l l e e
Introduction Introduction ........ ................. ..................
AC Volts AC Volts Troubleshooting Troubleshooting.........
Overload, Floating, or Noisy Readings on All Ranges......... Overload, Floating, or Noisy Readings
Inaccurate Readings on Inaccurate Readings on All Ranges
Overload, Inaccurate, Floating or Noisy Readings Overload, Inaccurate, Floating or Noisy Readings
on on Some Some Ranges Ranges .........
AC Current AC Current Troubleshooting Troubleshooting........
Overload Protection Circuitry Troubleshooting Overload Protection Circuitry Troubleshooting ..........
Checking Checking the the A/D A/D Controller Controller ........
the AC Volts and Volts and AC
(i.e., (i.e., what what fails). fails).
These functions must These function s must be good
CAUTION CAUTION
which are are extremely extremely
failures failures due due to to static static
especially important important that
d, Inaccurate,
on all or some ranges. me ranges. The
have have the the failures failures
paragraph 7-31 for a
failures). Unless Unless otherwise
for the the following
or Noisy Readings on Readings on All
caused if one of the
SERVICE GROUP B SERVICE GROUP B
Service Group B Contents Service Group B Contents
.................. .................. .................. ..................
.................. .................. ..................
on All Ranges...........7-B-5
All Ranges .......... ....................
.................. .................. ..................
................. .................. ..................
................. .................. ..................
verter is saturated. verter is
there is an open circuit in th there is an o
AC
readings can be caused by any of the amplifiers in the readings can be caused by any of the amplifiers in the
converter. converter.
Before Before
7-B-7. Before troubleshoo 7-B-7.
make sure relay K104 (see Schematic 1) is good and is make sure relay K104 (see Schematic 1) is good and is
energized (5V dc acro energized
be good, ,
energized, energized, U102
U102, make sure the A/D Cont U102, make sure
to paragraph 7 to paragraph 7-B-16 to check U462.
the following procedure. the following procedure.
a. a. Set the 3478A t
3V Range. 3V Range.
b. b. Apply
that
3478A's INPUT Terminals. 3478A's INPUT Terminals.
c. c. Using a stable
measure for approximately + 3V dc measure for approximately + 3V dc at jumper JM302.
d. d.
following: following:
The
and and
for a
otherwise
following
All
A/D Hybrid (U403). A/D Hybrid (U403).
the
e. e. If the readin
noisy, measure for approximately .12V ac at jumper noisy, measure for approximately .12V ac at jumper
JM303. JM303. Make sure the r
stable. stable.
7-B-1 7-B-1
P P a a r r a a g g r r a a p p h h
.................. ............ ... ..7-B-1 ..7-B-1
.................. ................ ....... ..7-B-3 ..7-B-3
..7-B-5
.................... .......... ..7-B-8 ..7-B-8
.................. ............. .... ...7-B-10 ...7-B-10
.................. ........... .. ..7-B-12 ..7-B-12
.................. ..........7-B-14 ..7-B-14
.................. ........... .. ..7-B-16 ..7-B-16
saturated. A floating rea A floating reading can be cause
pen circuit in the AC to DC Converter. e AC to DC Converter. Noisy
Before troubleshooting the ting the AC to DC
(5V dc across the coil). ss the coil). If the
U102 may may be defect be defective.
the A/D Controller (U462) is
-B-16 to check U462. If K104 is good, do
Set the 3478A to the AC Volts Fun o the AC Volts Function and the
Apply a stable a stable 3V at 3V at 1KHz sine
Using a stable Digital Voltmeter Digital Voltmeter (like the 3456A),
If the If the reading is reading is a stable
1. 1. Apply 1V at Apply 1V at 1KHz to the 1KHz to the INPUT Terminals.
2. 2. If the If the test voltmeter test voltmeter now reads
dc at JM302, the AC to DC Converter is good. dc at JM302, the AC to DC Converter is good.
Make sure the DC Volts Function is operating Make sure the DC Volts Function is operating
correctly. correctly.
3. 3. If the DC If the DC Volts Function Volts Function is good, replace th
If the reading is other than ap g is other than approximately +3V or
Make sure the reading on the eading on the test voltmeter is
ding can be caused if
Noisy
AC to DC Converter, Converter,
If the relay is relay is not
ive. Before replacing Before r eplacing
roller (U462) is good. good. Go
If K104 is good, do
ction and the
1KHz sine wave to wave to the
(like the 3456A),
at jumper JM302.
a stable +3V dc, +3V dc, do the do the
INPUT Terminals.
now reads a stable +1V a stable +1V
is good, replace the e
proximately +3V or
test voltmeter is
d if
not
Go
the