HP 3478A Technical Manual page 90

3478A
Figure 7-D-5. U462 ALE Signal
Other failures are normally noted when, after doing a
Self-Test, the 3478A display's either "A:D SLOPE ERR"
or "A:D TEST FAIL". If an "A:D LINK FAIL" is displayed,
the failure is most likely in the Isolation Circuitry (go to
paragraph 7-D-44 for troubleshooting).
paragraphs have the failures and troubleshooting
information for the A/D Converter.
7-D-37. Overload, Constant Zero, Floating, or Noisy
Readings. Before troubleshooting the A/D Converter for
these failures, make sure the failures are not caused by
the 3478A's Input Circuitry.
follows this paragraph (the same procedure is also in
Service Group A). If the procedure has been performed
already, ignore the procedure and go to Flowchart D for
troubleshooting. If it has not been performed, do the
following:
a. Set the 3478A to the DC Volts Function and 3V
Range.
b. Turn Autozero off by pressing the blue Shift but-
ton and then the INT/TRIG (AUTOZERO) button.
c. Apply a stable + 3V dc to the INPUT Terminals.
d. With a Digital Voltmeter (like the 3456A)
measure for + O1V at JMIOI.
e. If the reading on the test voltmeter is a stable +
10V, the A/D Converter is at fault. Go to Flowchart D for
troubleshooting. If the reading is other than + O1V, go to
Service Group A for troubleshooting.
7-D-38. A/D Slope Error. When an "A:D SLOPE ERR"
is displayed on the 3478A, the most likely cause is the
A/D Converter (U403 and associated circuitry) or the A/D
Controller (U462).
troubleshooting. The procedure in the Flowchart checks
the different ports (using Signature Analysis) of the A/D
Controller (U462) and also checks the DAC (U465).
7-D-39. A/D Test Falls. If the message "A:D TEST
FAIL" is displayed, the A/D Converter fails its internal
test. Since this can be caused by the A/D Controller
The following
Do the procedure which
Go to Flowchart
(U403 and associated circuitry) or the A/D Controller
(U462), go to
procedure in the Flowchart checks the different ports
(using Signature Analysis) of the A/D Controller and also
checks the DAC (U465).
7-D-40. Input Hybrid (U102) Inoperative
7-D-41. An inoperative Input Hybrid can be caused by
the hybrid itself or when it receives wrong information
from the A/D Controller. To isolate the circuitry, do the
following:
a. Turn the 3478A off.
b. Move jumpers JM502, JM503, and JM403 to the
"D" position (JM403 pin 1 and 2), as shown in Figure 7-
D-7.
c. Obtain a Signature Analyzer. Set and connect
as follows (shown in Figure 7-D-7):
Start:
Stop:
Clock:
Hold:
Self-Test: Out
Gnd:
d. Turn the 3478A on and check for the following
signatures:
U462 pin 32: 7ACA
U462 pin 33: 20FO
U462 pin 34: 666H
e. If any signatures are wrong, U462 may be
defective. Go to Flowchart D for troubleshooting.
f. If the signatures are good, the Input Hybrid is
defective.
7-D-42. A/D Controller Troubleshooting
7-D-43. Do the following to check the A/D Controller
(U462).
a. Using a logic probe, check and make sure the
RESET line (U462 pin 4) is high.
b. If the RESET line is low, do the following:
D for
1. Make sure pin 1 of U462 is toggling.
2. If pin 1 is not toggling, the Isolation Circuitry
may be at fault.
troubleshooting.
3. If pin 1 is toggling, check for a low at U466
pin 3.
7-D-8
Flowchart D for troubleshooting.
TP401 (JM403 pin 6) (
TP402 (JM403 pin 5) (
TP403 (JM403 pin 4) (
Out
Ground Pin (next to C203)
Go to paragraph 7-D-44 for
TM 11-6625-3071-14
The
)
)
)