HP 3478A Technical Manual page 75

7-A-1. INTRODUCTION 7-A-1. INTRODUCTION
7-A-2. This Service 7-A-2. This Service Group has Group has the DC
Current tr Current troubleshooting oubleshooting information for
Service Group is symptoms oriented (i.e., what fails) with Service Group is symptoms oriented (i.e., what fails) with
two different le two different levels of vels of troubleshooting.
determines the general area of the 3478A that causes determines the general area of the 3478A that causes
the the failure failure and and the the
troubleshooting information for the area that fails. troubleshooting information for the area that fails.
Unless otherwise specified, refer to Schematic 1 when Unless otherwise specified, refer to Schematic 1 when
using the troubleshooting procedures. using the troubleshooting procedures.
The instrument contains CMOS Integrated The instrument contains CMOS Integrated
Circuits (e.g. U102) which are extremely Circuits (e.g. U102) which are extremely
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-A-3. PRE-TROUBLESHOOTING 7-A-3. PRE-TROUBLESHOOTING INFORMATION
7-A-4. 7-A-4. Before doing Before doing any
perform the following: perform the following:
a. a. Check the 347 Check th e 3478A's
Supplies and make sure they are stable, have the correct Supplies and make sure they are stable, have the correct
value, and are not oscillating. value, and are not oscillating. The power supplies are
follows (see Schematic 4): follows (see Schematic 4):
DC VOLTS AND DC CURRENT TROUBLESHOOTING DC VOLTS AND DC CURRENT TROUBLESHOOTING
T T i i t t l l e e
Introduction ........ Introduction ................. ..................
Pre-Troubleshooting Information Pre-Troubleshooting
DC DC Volts Volts Troubleshooting............ Troubleshooting.....................
Overload, Floating, Constant Zero (with input applied), Overload, Floating, Constant Zero (with input applied),
or Noisy Readings on or Noisy Readings on All Ranges
Constant Zero Readings (with no input applied) on Constant Zero Readings (with no input applied) on
All All Ranges Ranges .........
Overload, Constant Zero, Floating, or Noisy Readings Overload, Constant Zero, Floating, or Noisy
on Some on Some Ranges Ranges .........
Inaccurate Readings on All Ranges Inaccurate Readings on
Protection Protection Circuitry Circuitry Troubleshooting.......
Input Input Circuitry Circuitry Troubleshooting........... Troubleshooting....................
Overload Readings on All Ranges Overload Readings on All
Constant Zero Readings on All Constant Zero Readings on All Ranges.................
Floating Readings Floating Readings on All
Noisy Readings on Noisy Readings
DC DC Current Current Troubleshooting........... Troubleshooting....................
Checking the Checking the A/D A/D Controller Controller ........
the DC Volts and Volts and DC
information for the 3478A. the 3478A. The
troubleshooting. The first The first level
second second level level has has
CAUTION CAUTION
failures failures due due to to static static
especially important important that
INFORMATION
any troubleshooting troubleshooting procedures, procedures,
8A's Floating Floating Common Pow Common Power er
The power supplies are as
SERVICE GROUP A SERVICE GROUP A
Service Group A Contents Service Group A Contents
.................. .................. .................. ..................
Information ........ ................. ..................
.................. ..................
All Ranges .......... ....................
.................. .................. .................. .................. .................
.................. .................. ..................
All Ranges .......... .....................
Troubleshooting................. ....................
..................
Ranges ......... ...................
Ranges.....................
on All Ranges.................. Ranges............................
on All All Ranges.......... Ranges................... ..................
.................. ..................
................. .................. ..................
DC
The
level
specific specific b. b. Check and
are at the correct level are at t
be checked at U405 pin 6, the -10V supply at U404 pin 6, be checked at U405 pin 6, the -10V supply at U404 pin 6,
and the buffered +10V supply at JM201 (see Schematic and the buffered +10V supply at JM201 (see Schematic
3). 3).
c. c. Make sure t
contact and not open. contact and not open.
7-A-5. DC VOLTS 7-A-5.
that
7-A-6. 7-A-6.
Inaccurate, Constant Zero, Floating, or Noisy Readings Inaccurate, Constant Zero, Floating, or Noisy Readings
on all or on all or some ranges.
the failures and the troubleshooting procedures (see the failures and the troubleshooting procedures (see
paragraph 7-30 for a description of these failures). paragraph 7-30
7-A-7. 7-A-7. Overload, Floating, Constant
applied), or Noisy Readings on All Ranges applied), or Noisy Readings on All Ranges
7-A-8. 7-A-8. If a failure is noted
be caused by the Input Circuitry (Input Switching or be caused by the Input Circuitry (Input Switching or
DC/Ohms Input DC/Ohms Input Amplifier) or
as
determine the inoperative circuitry, do the procedure determine the inoperative circuitry, do the procedure
which follows this paragraph (the same procedure is which follows this paragraph (the same procedure is
7-A-1 7-A-1
P P a a r r a a g g r r a a p p h h
.................. ........... .. ...7-A-1 ...7-A-1
.................. .............. ..... ...7-A-3 ...7-A-3
.................. ............ ... ...7-A-5 ...7-A-5
................ ...... ...7-A-7 ...7-A-7
................ ........ ...7-A-9 ...7-A-9
Readings
.................. ............. .... ...7-A-11 ...7-A-11
................. ...... ...7-A-17 ...7-A-17
................. ....... ..7-A-19 ..7-A-19
.................. ............. .... ..7-A-21 ..7-A-21
.................... .......... ...7-A-23 ...7-A-23
.... ...7-A-25 ...7-A-25
............. ... ...7-A-27 ...7-A-27
................ ....... ...7-A-29 ...7-A-29
................ ....... ...7-A-31 ...7-A-31
.................. .......... . ...7-A-33 ...7-A-33
P P o o w w e e r r C C h h e e c c k k e e d d
S S u u p p p p l l y y a a t t
+ + 5 5 V V J J M M 7 7 0 0 1 1
- - 1 1 5 5 V V J J M M 7 7 0 0 2 2
+ + 1 1 5 5 V V J J M M 7 7 0 0 3 3
Check and make sure make sure the Referen
he correct level and quiet. and quiet. The +10V supply can
Make sure the Front/Re he Front/Rear Switch is making goo
DC VOLTS TROUBLESHOOTING TROUBLESHOOTING
Typical Typical DC DC Volts Volts Failures
some ranges. The following p The following paragraphs have
for a description of these failures).
Overload, Floating, Constant Zero (with input
If a failure is noted on all ranges, on all ranges, the failure can
Amplifier) or by th
TM 11-6625-3071-14 TM 11-6625-3071-14
V V o o l l t t a a g g e e
L L e e v v e e l l
+ + 4 4 . . 9 9 V V t t o o + + 5 5 . . 1V 1V
- - 1 1 4 4 . . 4 4 V V t t o o - - 1 1 5 5 . . 6 6 V V
+ + 1 1 4 4 . . 4 4 V V t t o o + + 1 1 5 5 . . 6 6 V V
the Reference Supplies ce Supplies
The +10V supply can
ar Switch is making good d
Failures are are Overload, Overload,
aragraphs have
Zero (with input
the failure can
by the A/D Conv e A/D Converter. erter. To To