HP 3478A Technical Manual page 89

3478A
g. The RAM can be checked by reading data back
from it. One caution when checking the RAM, the data in
the RAM will be lost and the 3478A will need to be
recalibrated. Do the following:
1.To check the RAM, leave the Start and Stop
inputs of the Signature Analyzer connected as in step c,
but connect the Clock to TP5 (
2. Using a flat blade screwdriver, set the front panel
CAL ENABLE Switch to the calibration enable position
(the slot of the switch is in the vertical position, as shown
on the front panel).
3. Take the following signatures. U512 pin 9: H709
U512 pin 11: C577 U512 pin 13: 4296 U512 pin 15:
8U25
4. If the signatures are wrong, the RAM may be
defective. Before replacing the RAM, make sure the
RAM's R/W line reads a signature of 4296.
signature is wrong, replace U515.
good, replace U512.
5. If the signatures are good, other circuitry may
cause the failure. Go to Flowchart A (see paragraph 7-
D-I 1) for further troubleshooting.
7-D-25. Voltmeter Complete
7-D-26. The Voltmeter Complete pulse is normally out-
put after an input measurement is completed.
troubleshoot the operation, with a logic probe, check and
make sure pin 25 of US01 is toggling. If the probe does
not show toggling, US01 is most likely defective. If the
probe shows toggling, make sure R538 is not open, and
CR504 and CR505 are not shorted. If the resistor and
diodes are good, replace U508.
7-D-27. Address Switch Failure
7-D-28. An address switch failure can be caused by the
switch itself or US10. The address switch can easily be
checked using a logic probe. With all switches of the ad-
dress switch on (up), pins 9, 10, 11, 12, 13, 14, 15, and
16 of the switch are low. With all switches off (down),
the pins are high. If the switch is good, replace US10.
7-D-29. External Trigger
7-D-30. An external trigger failure can be caused by a
defective U514 or HP-IB Chip. Do the following:
a. Set the 3478A to the Single Trigger mode.
b. Using a logic probe, make sure pin 5 of U514 is
high. If the pin 1s low, do the following:
).
If the
If the signature is
To
1.Check for a low at pin 4 of U514.
2.If pin 4 of U514 is low, replace U514.
3.If pin 4 of U514 is high, replace U503.
c. If pin 5 of U514 is high, using a logic pulser,
pulse (i.e., toggle) pin 5.
d. Using a logic probe, check for a high at pin 9 of
U514.
e. If pin 9 is low, replace US14. If the pin 1s high,
while checking the pin with a logic probe, apply a trigger
pulse to the 3478A's EX TRIG connector (i.e., short the
input of the connector to ground). When the 3478A is
triggered, pin 9 of U514 should toggle high and then low.
f. If pin 9 does not toggle, replace U514. If it does
toggle, USO1 may be defective.
7-D-31. FLOATING COMMON LOGIC FAILURES
7-D-32. Floating Common Failures can be failures in the
A/D Converter and the A/D Controller.
paragraphs have the failures and troubleshooting
information.
7-D-33. Pre-Troubleshooting Information
7-D-34. Before troubleshooting the Floating Common
Logic Circuitry and A/D Converter, perform the following:
a. Check the 3478A's Floating Common Power
Supplies. Make sure they are stable, are at the correct
level, and are not oscillating. The power supplies are as
follows:
Power
Supply
+ 5V
-15V
+ 15V JM703
b. Check and make sure the Reference Supplies
are at the correct level and are quiet. The + 10V supply
can be checked at U405 pin 6, the -10V supply at U404
pin 6, and the buffered + 10V supply at JM201.
c. Make sure the ALE line at TP403 (U462 pin 11)
is good, as shown in Figure 7-D-S.
missing or incorrect, make sure the CPU's clock (at pin 2
and 3 of U462) is at 10.98MHz. Try replacing crystal
Y460, if the signal is missing. If still missing, replace
U462.
7-D-35. A/D Converter Failure and Troubleshooting
7-D-36. An A/D Converter failure can show up as
Overload, Constant Zero, Floating, or Noisy Readings.
7-D-7
TM 11-6625-3071-14
Checked Voltage
at level
JM701 + 4.9V to + 5.1V
JM702 -14.4V to - 15.6V
+ 14.4V to - 15.6V
If the signal is
The following