HP 3478A Technical Manual page 76

3478A 3478A
also in Service Group also in Service Group D).
performed already, ignore the procedure and go to performed already, ignore the procedure and go to
paragraph 7-D-21 for troub paragraph 7-D- 21 for troubleshooting.
performed, do the following: performed, do the following:
a. a. Set the 3 Set the 3478A to the DC 478A to the DC Volts Function and t
3V Range. 3V Range.
b. b. Turn Autoz Turn Autozero off ero off by
button and then the INT/TRIG (AUTOZERO) button. button and then the INT/TRIG
c. c. Apply a s Apply a stable + 3V dc to t table + 3V dc to the INPUT Terminals.
d. d. With With a a Digital Digital Voltmeter
measure for +10V at JM101. measure for +10V at JM101.
e. e. Make sure the read Make sure the reading on the test vo
stable +10V. If the stable +10V. If the reading on reading on the test
stable +10V, the A/D Convert stable +10V, th e A/D Converter is at fault.
Group D for troubleshooting. Group D for troubleshooting.
f. f. If the reading on If the reading on the test
(overload, constant zero, floating, or noisy), unsolder and (overload, constant zero, floating, or noisy), unsolder and
lift the end of jumper JM101 which is connected to the lift the end of jumper JM101 which is connected to the
A/D Converter (toward the rear of the 3478A). A/D Converter (toward the rear of
g. g. If the read If the reading on the ing on the test voltmeter is no
the A/D Converter is at the A/D Conv erter is at fault.
troubleshooting. troubleshooting.
h. h. If the If the reading is st reading is still wrong, t
(Input Switching and DC/Ohms Input Amplifier) is at fault. (Input Switching and DC/Ohms Input Amplifier) is at fault.
Go to paragraph 7-A-21 for troubleshooting. Go to paragraph 7-A-21 for
i. i. Replace jum Replace jumper J per JM101.
7-A-9. 7-A-9. Constant Zer Constant Zero Readings ( o Readings (with no inp
on All Ranges on All Ranges
7-A-10. 7-A-10. Since the Since the 3478A's 3 3478A's 30V and
normally have a constant zero reading with no input normally have a constant zero reading with no input
applied, the other ranges will also be at zero if relay K102 applied, the other ranges will also be at zero if relay K102
is shorted. is shorted. Make sure the relay Make sure the relay is good and is not being
turned on by turned on by U102 (zero volts across th U102 (zero volts across the coil of K102).
the relay is turned on in the 30mV through 3V Ranges, the relay is turned on in the 30mV through 3V Ranges,
U102 may be defectiv U102 may be defective. e. Before replacing
sure the A/D Controller (U462) is good. sure the A/D Co ntroller (U462) is good. Go to paragraph
7-A-33 for the SA procedure to check U462, before 7-A-33 for the SA procedure to check U462, before
replacing the hybrid. replacing the hybrid.
7-A-11. 7-A-11. Overload, Constant Overload, Constant Zero, Floating,
Readings on Some Ranges Readings on Some Ranges
7-A-12. The Input Hy 7-A-12. The Input Hybrid (U102) in brid (U102) in conjunction with th
Input Relays (KI01 through K104) is used to select Input Relays (KI01 through K104) is used to select
different paths to connect the input signals with the different paths to connect the input signals with the
DC/Ohms Input Amplifier. DC/Ohms Input Amplifier. The hy
select the amplifier's different gain configurations. select the amplifier's different gain configurations.
Because of this, a relay or U102 can make certain Because of this, a relay or U102 can make certain
ranges fail. ranges fail.
D). If the If the procedure has procedure has been
leshooting. If it has If it has not been
Volts Function and the
by pressing the pressing the blue Shift blue Shift
(AUTOZERO) button.
he INPUT Terminals.
Voltmeter (like (like the the 3456A)
ing on the test voltmeter is a ltmeter is a
the test voltmeter is a voltmeter is a
er is at fault. Go to Service Go to Service
the test voltmeter is voltmeter is wrong
the 3478A).
test voltmeter is now good,
fault. Go to Service Group D for Go to Service Group D for
ill wrong, the Input he Input Circuitry
troubleshooting.
M101.
with no input applied) ut applied)
0V and 300V Ranges 300V Ranges will
is good and is not being
e coil of K102). If If
Before replacing U102, make U102, make
Go to paragraph
Zero, Floating, or Noisy
conjunction with the e
The hybrid is brid is also used also used to to
been 7-A-13. Overload. 7-A-13. Overload. An ov
DC/Ohms Input Amplifier's feedback circuitry is open. DC/Ohms Input Amplifier's feedback circuitry is open.
Since the feedback circuitry is in U102, the Since the feedback circuitry is in U102, the hybrid is most
not been
likely de likely defective.
A/D Contro A/D Controller (U462) is
he for the SA procedure to check for the SA procedure to check U462, before replacing the
hybrid. hybrid.
7-A-14. 7-A-14.
cause is the I cause is
U102, make sure U102, make sure the A/D Cont
to paragraph 7-A-33 for the SA procedure to check to paragraph 7-A-33 for the SA procedure to check
U462, before replacing the hybrid. U462, before replacing the hybrid.
3456A)
7-A-15. 7-A-15.
normally caused when an input path to the DC/Ohms normally caused when an input path to the DC/Ohms
Input Amplifier is open. Input Amplifier
a. a.
defective, do the following: defective, do the following:
wrong
is energiz is energized (5V
energized, replace the energized,
w good,
defective. Go to para defective.
U102. U102.
U102 may U102 may be defective
Circuitry
before replacing U102. before replacing U102.
b. b. If the 30V
the following: the following:
is energiz is energized (5V
will
energized, replace the energized,
defective. Go to para defective.
U102. U102.
U102 may be defective U102 may
before replacing U102. before replacing U102.
7-A-16. Noise. 7-A-16. Noise. Noise can
internal to the Input Hybrid (U102) an internal to the I
U101 and then U102 if noise is noted on some ranges. U101 and then U102 if noise is
or Noisy
7-A-17. 7-A-17. Inaccurate Readings
7-A-18. Inaccurate rea 7-A-18.
than than positive full positive full scale reading
3478A is calibrated using zero and positive full scale (or 3478A is calibrated using zero and positive full scale (or
1/3 scale) inputs. s. Inaccurate read 1/3 scale) input
the Input Circuitry (Input Hybrid or DC/Ohms Input the Input Circuitry (Input Hybrid or DC/Ohms Input
Amplifier). Try replacing U1 Amplifier).
7-A-2 7-A-2
An overload erload condition
fective. Before replacing Before replacing U102, make sure
ller (U462) is good. good. Go to paragraph
U462, before replacing the
Constant Constant Zero Zero Reading. Reading.
the Input nput Hybrid Hybrid (U102). (U102).
the A/D Controller (U462) is roller (U462) is good.
Floating Readings. Floating Readings.
is open. Check for t Check for the following:
If If the the 30mV, 30mV, 300mV, 300mV, and
1. 1. Short across the Short across the contacts of relay contacts of relay K101.
2. 2. If the ran If the ranges are now ges are now good, make sure
ed (5V dc across dc across the coil).
replace the relay. relay. If not, U1
Go to paragraph 7-A-33 be graph 7-A-33 before replacing
3. 3. If, after If, after replacing K101, replacing K101, the rang
be defective. . Go to
If the 30V and 300V Ran and 300V Ranges are defective,
1. 1. Short across the Short across the contacts of relay contacts of relay K102.
2. 2. If the If the ranges are now ranges are now good, make sure
ed (5V dc across dc across the coil).
replace the relay. relay. If not, U1
Go to paragraph 7-A-33 be graph 7-A-33 before replacing
3. 3. If, after If, after replacing K102, replacing K102, the rang
be defective. . Go to
Noise can be caused be caused by a
nput Hybrid (U102) and UI01.
noted on some ranges.
Inaccurate Readings on All Rang on All Ranges
Inaccurate readings normally dings normally show up
scale readings. s. This is becau
Inaccurate readings can be caused
Try replacing U101 and then 01 and then U102.
TM 11-6625-3071-14 TM 11-6625-3071-14
condition exists if exists if the the
hybrid is most
U102, make sure the the
Go to paragraph 7-A-33 7-A-33
The most The most likely likely
Before replacing Before r eplacing
good. Go Go
A A floating floating reading reading is is
he following:
and 3V R 3V Ranges a anges are re
K101.
good, make sure KI01 KI01
the coil). If K101 If K101 is is
If not, U102 may be 02 may be
fore replacing
the ranges still fail, es still fail,
Go to paragraph paragraph 7-A-33 7-A-33
ges are defective, do do
K102.
good, make sure K102 K102
the coil). If K102 If K102 is is
If not, U102 may be 02 may be
fore replacing
the ranges still fail, es still fail,
Go to paragraph paragraph 7-A-33 7-A-33
by a FET switch FET switch
d UI01. Replace Replace
es
show up as other as other
This is because the se the
ings can be caused by by
U102.