HP 3478A Technical Manual page 78

3478A 3478A
Hybrid or the DC/Ohms Input Amplifier. Hybrid or the DC/Ohm s Input Amplifier. 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. Make sure Autoz Make sure Autozero is turned o
7-A-8 step b). 7-A-8 step b).
c. c. If the reading If the reading on the 3478A on the 3478A is quiet with Autoze
off, the I off, th e Input nput Hybrid Hybrid is defect is defective.
reading is still noisy, continue with the next step. reading is still noisy, continue with the next step.
d. d. Connect pin 6 a Connect pin 6 and pin 2 (U102 p
U101 to each other. U101 to each other.
e. e. Apply a stab Apply a stable +3V
Terminals. Terminals.
f. f. Using a Using a high impeda high impedance Digital
the 3456A) measure for a stable +3V at U101 pin 3. the 3456A) measure for a stable +3V at U101 pin 3.
g. g. If the volta If the voltage is noisy, ge is noisy, replace the I
(U102). (U102).
h. h. If the volta If the voltage is stable, measure for a ge is stable, measure for a stable +3V
at pin 6 of U101. at pin 6 of U101.
i. i. If If the the voltage voltage is is noisy,
voltage is stable, replace U102 (Input Hybrid). voltage is stable, replace U102 (Input Hybrid).
7-A-31. 7-A-31. DC DC CURRENT CURRENT TROUBLESHOOTING
7-A-32. Make sure 7-A-32. Make sure the DC the DC Volts Function
correctly on all ranges, before troubleshooting for dc correctly on all ranges, before troubleshooting for dc
current failures. current failures. Go to pa Go to paragraph 7-A-5
for DC Volts Failures. for DC Volts Failures. If the D
the only components that can cause a current failure are the only components that can cause a current failure are
an open current fuse (F101), a defective resistor R107, an open current fuse (F101), a defective resistor R107,
or the Input Hybrid U102. or the Input Hybrid U102. Make sure F101 and R107 are
good. If the good. If the resistor and resistor and fuse are go
defective. Before repla defective. Before replacing U102,
Controller (U462) is good Controller (U462 ) is good. . Go to
check the A/D check the A/D Controller. Controller.
replace U102. replace U102.
Do the following:
Volts Function and the
ero is turned off (see paragraph ff (see paragraph
is quiet with Autozero ro
ive. Replace U1 Replace U102. 02. If th
nd pin 2 (U102 pin 3 and 9) of in 3 and 9) of
le +3V to t to the 3478A' he 3478A's INPUT
nce Digital Voltmeter (like Voltmeter (like
replace the Input Hybrid nput Hybrid
stable +3V
noisy, replace replace U101. U101.
TROUBLESHOOTING
Volts Function is operating is operating
ragraph 7-A-5 to troubleshoo to troubleshoot t
If the DC Volts Function C Volts Function is good,
Make sure F101 and R107 are
fuse are good, U102 may od, U102 may be
cing U102, make sure make sure the A/D
Go to paragraph 7-A-3 paragraph 7-A-33 to
If th If the contr e controller is oller is good,
7-A-33. CHECKING THE 7-A-33.
he
7-A-34. 7-A-34. Do the
Refer to Schematic 3. Refer to Schematic 3.
a. a. Turn the
b. b. Move jumpers JM502
If the e
"D" position (JM403 pin 1 and 2), as shown in Figure 7- "D" position (JM403 pin 1 and 2), as shown in Figure 7-
A-1. A-1.
c. c. Obtain
as follows (shown in as follows (shown in Figure 7-A-1)
s INPUT
S S t t a a r r t t : :
S S t t o o p p : :
C C l l o o c c k k : :
H H o o l l d d : :
S S e e l l f f - - T T e e s s t t : :
G G n n d d : :
If If the the
is good,
d. d.
signatures. signatures.
U462 pin 32: 7ACA U462 pin 32: 7ACA
be
U462 pin 33: 20FO U462 pin 33: 20FO
the A/D
U462 pin 34: 666H U462 pin 34: 666H
3 to
good,
e. e. If any sig
D (Flowchart D) for troubleshooting. D (Flowchart D) for troubleshooting.
f. f. If the
defective. defective.
7-A-4 7-A-4
CHECKING THE A/D CONTROLLER A/D CONTROLLER (U482)
Do the following to following to check the A/D check the A/D Controller.
Turn the 3478A off 3478A off. .
Move jumpers JM502, JM503, an , JM503, and JM403 to th
Obtain a a Signature Signature Analyzer. Analyzer. Set
Figure 7-A-1): :
T T P P 4 4 0 0 1 1 ( ( J J M M 4 4 0 0 3 3 p p i i n n 6 6 ) ) ( (
T T P P 4 4 0 0 2 2 ( ( J J M M 4 4 0 0 3 3 p p i i n n 5 5 ) ) ( (
T T P P 4 4 0 0 3 3 ( ( J J M M 4 4 0 0 3 3 p p i i n n 4 4 ) ) ( (
O O u u t t
O O u u t t
G G r r o o u u n n d d P P i i n n ( ( n n e e x x t t t t o o C C 2 2 0 0 3 3 ) )
Figure 7-A-1. Figure 7-A-1. JM403 SA JM403 SA Connection
Turn the Turn the 3478A o 3478A on and n and check the
If any signatures are wr natures are wrong, go to Service Group
If the signatures ar signatures are good, e good, the Input
TM 11-6625-3071-14 TM 11-6625-3071-14
(U482)
Controller.
d JM403 to the e
Set and and connect connect
) )
) )
) )
Connection
check the following following
ong, go to Service Group
the Input Hybrid is Hybrid is