Inguard Logic And Failure Symptoms - HP 3456A Operating And Service Manual

8·8·1. GENERAL.
8-8-2. This Service Group has troubleshooting infor­
mation for the 3456A's Inguard Logic (including the In­
guard Isolation Logic) and AID circuitry. Make sure
the 3456A's Outguard
troubleshooting for any Inguard Failures. Go to Service
Group A for the Outguard's
Troubleshooting.
8-8-3. The Service Group is symptoms oriented (what
fails) with different levels of troubleshooting. The first
level determines the faulty area and the other levels has
troubleshooting information for the areas.
8·8·4. INGUARD IlDGIC AND AIDI FAILURE SYMPTDMS.
8-B-5. An Inguard Failure can be determined by the
following symptoms.
8·B·6. Th. 345&A Displ.y. Dish
8-B-7. This
symptom occurs
Outguard Isolation Logic, Inguard Isolation Logic, or
the Inguard (Analog or Digital) fails. To help determine
the faulty circuitry, press the front panel TEST button
and check for the following:
a. Test 113 fails. This test shows an Isolation Logic
Failure in either the Inguard or Outguard. To determine
the faulty circuitry, do the following:
1 . Turn the 34.56A Off.
2. Unplug the cable from the Isolation Logic Con­
nector (A3J7, Schematic 12).
3. Connect pin 1 to 2 and pin 3 to 4 on the Isolation
Logic Connector. I f the Isolation Logic Test
Jumper. -hp- Pan No. 034.56-61602 is available,
plug it into 17 instead of shorting the pins.
4. Turn the 34.56A On.
.5. Press the TEST button and then set the 34.56A to
Test 113 by pressing the 3, STORE, and .5
(COUNT) keys.
6. I f Test 113 still fails, the Outguard Isolation Logic
is at fault. Go to Service Group A, Paragraph
8-A-37 for troubleshooting. If the Test passes, go
to Paragraph 8-8-32 for troubleshooting.
b. Test 114 or Test 117 fails. I f any of these tests fail,
the failure can be in the AID Converter or the Analog
Circuitry (Input Switching or Input Amplifier). This
failure can also show up as an Overload. Go to
Paragraph 8-8-8 to determine the faulty circuitry.
SERVICE GROUP B
Logic is good before
Failures and
1- -
..
- - - -I.
when the 3456A's
8·8·8. DverlGld Failure or Constlnt Zero Displlyed (1lso #7 failsl.
if rest #4 or rest
8-B-9. If an Overload Failure is noted, a Constant Zero
is displayed. or Test 114 or Test 117 fails, the failure can
be in the AID Converter, Inguard Logic, Input
Amplifier, or Input Switching. To determine the faulty
circuitry, do the following:
Determine the type of failure.
a.
b. I f an Overload Failure is noted, do the following:
I . Turn the 34.56A Off.
2. Move A30H.5 to the Non-Run (2 and 3) position
(Schematic 8).
3. Turn the 34.56A On.
4. If the Overload disappears and the instrument is
working correctly, the Overload Circuitry in the
AID Converter is at fault. Check for a shorted
AlOC41O. Replace C41O, if shorted. I f the
capacitor is good, replace U409.
.5. I f the Overload remains, return 13.5 to the Run
position and continue with the next step.
c. If Test 114 or Test #7 fails (or an Overload is still
noted), do the following:
I . Press the 34.56A's RESET button.
2. Set the instrument to the 10 V range and the 6
Digit Mode (by storing 6 into the N DIGIT DISP
Register).
3. Place jumper A20J29 in the GND test position, as
shown in Figure 8-B-I (Schematic 4).
u�oo
Figure 8·8·1. rest Jumper A20J29 in Ground Position.
4. Turn Autozero Off. The 34.56A should display a
stable zero reading ( ± 3 count).
.5. I f other than zero is displayed. the AID Converter
or Inguard Logic is at fault. Go to Paragraph
8-B-16 for further isolation.
6. I f a stable zero is displayed, continue with Step d.
0
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z
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J29
0 0 0
8-8-1