HP 3478A Technical Manual page 73

3478A 3478A
7-29. The correct Service Group 7-29. The correct Service Group is selected according t
failure. Once the failure failure. Once the failure has been det
recommended recommended group. group.
possible failures, general troubleshooting information, possible failures, general troubleshooting information,
and corresponding and corresponding Service Service Group(s).
Groups are also listed in Table 7-1. Groups are also listed in
7-30. 7-30. DC Volts DC Volts and and DC
Group A). Group A). Typical DC Typical DC Volts and
are Overload, Inaccurate, Constant Zero, Floating, or are Overload, Inaccurate, Constant Zero, Floating, or
Noisy Noisy Readings. Readings. Troubleshooting in Troubleshooting information for
failures is in failures is in Service Group A. Service Group A. The following expla
failures. failures.
a. a. Overload. Overload. An overload An o
reading taken by the instrument appears to be larger reading taken by the instrument appears to be larger
than the input than t he input actually actually is. is.
saturated DC/Ohms Input Amplifier or by the A/D saturated DC/Ohms Input Amplifier or by the A/D
Converter. Converter.
b. b. Inaccurate Readings. Inaccurate Readings. Inaccurate
normally caused when the measurement circuitry is not normally caused when the measurement circuitry is not
linear. linear. This is This is because t because the 3478
zero and full scale inputs. zero and full scale inputs. Therefore, the
zero readings must be good, but any other reading can zero readings must be good, but any other reading can
be inaccurate. be inaccurate.
c. c. Constant Zero Reading. Constant Zero Reading.
reading is normally caused when either the input to the reading is normally caused when either the input to the
DC/Ohms Input Amplifier or the input to the A/D DC/Ohms Input Amplifier or the input to the A/D
Converter is shorted to ground (common). Converter is shor ted to ground (common). It can also be
caused if no runup is done by the A/D caused if no runup is done by the A/D Converter.
d. d. Floating Reading. Floating Reading. A floa
the 3478A displays a certain reading (with no input the 3478A displays a certain reading (with no input
applied) which does not change, after an input is applied applied) which does not change, after an input is applied
to the multimeter. to th e multimeter. This can be caused This can
Converter and if there is an open in the Input Circuitry. Converter and if there is an open in the Input Circuitry.
e. e. Noisy Noisy readings readings can
Circuitry and A/D Converter. Circuitry and A/D Converter.
7-31. 7-31. AC Volts AC Volts and AC Current Failures (Service and AC Current Failures (Service
Group B). Group B). AC Volts AC Volts and AC and AC Current
Overload, Inaccurate, Floating, or Noisy Readings. Overload, Inaccurate, Floating, or Noisy Readings.
Troubleshooting information for these failures is in Troubleshooting information for these failures is in
Service Group B. Service Group B. Before going Before going to the
check and make sure the DC Volts and DC Current check and make sure the DC Volts and DC Current
Function is operating corr Function is operating correctly.
Current failures are explained in paragraph 7-30. Current failures are explained in
following explains the AC Volts and AC Current Failures. following explains the AC Volts and AC
a. a. Overload. Overload. An An overload
reading taken by the instrument appears to be larger reading taken by the instrument appears to be larger
than the input than th e input actually actually is. is.
saturated AC to DC Converter or the A/D Converter. saturated AC to DC Converter or
b. b. Inaccurate Readings. Inaccurate Readings. Inaccurate
normally caused when the AC to DC Converter has poor normally caused when the AC to DC Converter has poor
frequency response. frequency response.
is selected according to o
has been determined, go t ermined, go to the
The following The following paragraphs paragraphs lists
Group(s). The Service The
Table 7-1.
DC Current Current Failure Failure (Service
Volts and DC Current DC Current Failures
formation for these
The following explains the
verload is caused is caused when when the
This can be caused by This can be ca used by a a
Inaccurate readings readings are
he 3478A is calibrat A is calibrated using ed using
Therefore, the full scale and full scale and
A A constant constant zero
It can also be
Converter.
A floating ting reading reading is w
be caused by t by the A/D
can be be caused caused by by the the Input
Current Failures can Failures can be
to the service group, service group,
ectly. The DC Volts The DC Volts and DC
paragraph 7-30. The
Current Failures.
overload is caused is caused when when the
This can be cau This can be caused by sed by a a
the A/D Converter.
Inaccurate readings readings are
c. c. Floating Reading.
o the the 3478A displays a certain reading (with no input the 3478A displays a certain reading (with no input
lists applied) which does not change, after an input is applied applied) which does not change, after an input is applied
to the multimete to the multimeter. r. This can be caused if there is an ope
Service circuit in the AC to DC Converter or A/D Converter. circuit in the AC to DC Converter or A/D Converter.
d. d. Noisy Readings.
by the amplifiers and the RMS Converter in the AC to by the amplifiers and the RMS Converter in the AC to DC
(Service
Converter. Converter.
Failures
7-32. 7-32.
these
Ohms Failures can be Overload, Inaccurate, Floating, or Ohms Failures can be Overload, Inaccurate, Floating, or
ins the
Noisy Readings. Noisy Readings. Troubleshooting
failures is failures is in Serv
service group, check and make sure the DC Volts and service group, check and make sure the DC Volts and
the
DC Current DC Current Functions are
Volts and DC Current failures are explained in Volts and DC Current failures are explained in paragraph
7-30. 7-30. The following explains The following explains the Ohms
a. a.
reading taken by the instrument appears to be larger reading taken by the instrument appears to be larger
are
than the than the input actu
ohms current ohms current is too
Amplifier or the A/D Converter can also cause an Amplifier or the A/D Converter can also cause an
overload, make sure the DC Volts Function is operating overload, make sure the DC Volts Function is operating
correctly (go to paragraph 7-30 correctly (go to
b. b.
readings can be caused if the ohms current changes readings can be caused if the ohms current changes
zero
value value under differe
caused if caused if the measurement
sure the DC Volts Function is operating correctly (go to sure the DC Volts Function is operating correctly (go to
paragraph 7-30, if the function fails). paragraph 7-30
c. c.
is when hen
reading is normally caused when the Ohms Current reading is normally caused when the Ohms Current
Source does not supply Source does
can also be caused when either the input to the can also be caused when either the input to the
he A/D
DC/Ohms Input Amplifier or the input to the A/D DC/Ohms Input Amplifier or the input to the A/D
Converter is shorted Converter
the DC Volts Function is operating correctly (go to the DC Volts Function is operating correctly (go to
Input
paragraph 7-30, if the function fails). paragraph 7-30
d. d. Floating Reading.
the 3478A displays a certain reading (with no input the 3478A displays a certain reading (with no input
be
applied) which does not change, after an input is applied applied) which does not change, after an input is applied
to the multimeter. to the
Converter and the In Converter an
ohms failure, make sure the DC Volts Function is ohms failure, make sure the DC Volts Function is
operating correctly (go to operating correctly (go to paragraph 7-30
and DC
fails). fails).
The
e. e. Noisy Readings.
by a noisy ohms current. by a noisy ohms current.
the
7-33. 7-33.
Group D). Group D). Chassis Common
Turn-On, Display, Keyboard, Control ROM, Calibration Turn-On, Display, Keyboard, Control ROM, Calibration
RAM (CMOS RAM), HP-IB Failures, and miscellaneous RAM (CMOS RAM), HP-IB Failures, and miscellaneous
are
failures failures
7-3 7-3
Floating Reading. A A floating
This can be caused if there is an open n
Noisy Readings. Noisy Noisy readings can
Ohms Ohms Failures Failures (Service (Service Group
Troubleshooting information for
in Service Group ice Group C. C.
Functions are operating correct operating correctly. ly. The DC
the Ohms Failures.
Overload. Overload. An overload An overload is caused
input actually is. ally is. This can be This can be caused if the
is too large. large. Since the Since the DC/Ohms Input
paragraph 7-30, if the function fails).
Inaccurate Readings. Inaccurate Readings.
under different loads. nt loads.
the measurement circuitry circuitry is not linear.
, if the function fails).
Constant Zero Reading. Constant Zero Reading.
not supply any oh any ohms current.
is shorted to gro to ground (common). und (common). Make sure
, if the function fails).
Floating Reading. A A floating
multimeter. This can also be ca This can also be caused by
d the Input Circuitry put Circuitry. . Since this is
paragraph 7-30, if the function
Noisy Readings. Noisy r Noisy readings can
Chassis Chassis Common Common Logic
Chassis Common Logic Failures
(e.g. (e.g. Voltmeter Voltmeter
TM 11-6625-3071-14 TM 11-6625-3071-14
floating reading reading is wh is when
readings can be caused be caused
DC
Group C). C). Typical Typical
information for these these
Before going to t Before going to the
The DC
paragraph
Failures.
is caused when when the
caused if the
DC/Ohms Input
, if the function fails).
Inaccurate Inaccurate ohms ohms
Inaccuracy Inaccuracy can also can also be
is not linear. Make Make
A A constant constant zero zero
ms current. The failure The failure
Make sure
floating reading reading is w is when hen
used by the A/D the A/D
Since this is not an not an
, if the function
eadings can be caused be caused
Logic Failures Failures (Service (Service
Logic Failures consists of consists of
Complete, Complete, Exter- Exter-
en
he
the
be