A/D Troubleshooting; Overload Failure - HP 3456A Operating And Service Manual

Model 3456A
c. Unplug the cable from the Isolation Logic Connec­
tor (A3J7, Schematic 12).
d. Do the following on the A30 Assembly (Schematic
8),
I . Move A30J331 J34 to the 2" (middle) position, as
shown in Figure 8-8-2.
•
J 33
•
2
•
figure 8-8·2. Jumper A30J33/34 in the 2 Position.
2. Move A30J35 and J36 to the Non-Run (2 and 3)
position.
e. Connect (to A30 Assembly) and set the Signature
Analyzer as follows (Schematic 8):
Start: A30J31 -STR
A30J3I-STP
Stop:
A30J32-A
Clock:
Gnd:
A30J3I-GND
Hold:
Self-Test:
f. Turn the 3456A On and make sure SA is working
correctly by checking the + 5 V signature (85AA). If the
signature is wrong, make sure the SA connections are
good. If still wrong, the Inguard Logic is at fault. Go to
Paragraph 8-8-32 for troubleshooting. If the signature
is correct, continue with the next step.
g. Check the following Signatures in the AID cir­
cuitry (A20 Board, Schematic 4):
Signature
9PHA
5H70
5AF3
POl2
h. Check for a "85AA" signature at A20P30 Pin 5 .
Make sure the S A probe shows toggling. This is the
ALE line which is the clock signal for the AID Con­
vener.
i. If any of the signatures are wrong, the failure is in
the Inguard Logic. Go to Paragraph 8-8-32 for
troubleshooting. If the signatures are good, the failure
is most likely in the AID Circuitry. Go to Paragraph
8-B-18 for troubleshooting.
•
J
•
_Jumper
•
UN
OUI
Oul
Checked at
A20U408 Pin 4
A20U408 Pin 6
A20U408 Pin 8
A20U408 Pin 10
8-8·18. AID TROUBLESHOOTING.
8-8-19. The AID Converter in the 3456A can cause
Overload, Accuracy, Zero, or Noise Failures. The Con­
verter consists of both analog and digital circuitry. The
analog circuitry, consisting of an Integrator, Slope
Amp, and Comparator, does the AID conversion. The
digital circuitry controls the operation. Either circuitry
can cause the AID Failures. The following paragraphs
have the failures and troubleshooting information.
NOTE
The AID Converter may have to be repadd­
ed according to the AID A d justment Pro­
cedure in Service Group F , if any com­
ponents are replaced in the converter.
8·8-20. Overload failure.
8-8-2 1 . An Overload Failure can be caused by the
analog or digital circuitry in the AID Converter. The
Digital Circuitry troubleshooting is in Paragraph
8-8-27. The procedure to isolate the Digital Circuitry
from the Analog Circuitry
troubleshooting information, is as follows. Do the
following:
a. Make sure the Overload Failure in the 3456A is not
caused by the AID Overload Circuitry. A procedure to
isolate the circuitry is in Paragraph 8-B-8, step b. If the
procedUre in the paragraph has been done, continue
with the next step.
b. Turn the 3456A Off.
c. Make sure the FrontlRear Switch of the instru­
ment is in the FRONT position.
d. Make sure the cable from the Isolation Logic Con­
nector (A3J7) is unplugged (Schematic 12).
e. Make sure A30J35 and J36 are in the Non-Run (2
and 3) position (Schematic 8).
f. Make sure A30J331 J34 is in the " I " (Run) posi­
tion (Schematic 8).
g. Place the AID Test Jumper A20J29 (Schematic 4)
in the GND position, as shown in Figure 8-8-1.
h. Turn the 3456A On.
i. Connect the vertical input of an oscilloscope to
A2OTP405 (use ground #4 as low). With the scope in the
external trigger mode, connect the trigger input to
TP404. Using the scope set-up information in Figure
8-8-3, check the waveform shown in the figure
(Schematic 4).
j. If the waveform is good, the AID Digital Circuitry
is good. The analog circuitry may be defective. Go to
step m.
k. If the waveform is wrong or not present, the AID
Analog or Digital Circuitry is the cause. The faulty area
Service
and the analog
B·B·3