A/D Digital Circuitry Troubleshooting; Inguard Logic Troubleshooting - HP 3456A Operating And Service Manual

Model 34.56A
2. Make sure the A30 Assembly is still removed
from the instrument.
3 . Connect pin 1 0 o f U408 to ground.
4. Place jumper A 10129 in the GND test position,
as shown in Figure 8-8-1.
5 . Turn the 34.56A On.
6. Using a logic pulser, toggle pin 9 of U40 1 .
7. Using the test voltmeter, measure between the
sources and drains of the input FETs (Q402 and
Q403) . Make sure the voltage does not exceed
I mY. Alos make sure the voltage is stable
« 2 p,V change). Replace Q402 or Q403, if the
vollages are wrong.
f. I f the previous checks are good and the 34.56A is
still inaccurate or noisy, try replacing the lmegrator
Capacitor (C403) or Resistor Network (U.500).
8·8·27. AID Digital Circuitry Troubleshooting.
8-8-28. The AID Digital Circuitry consists of a
decoder, latch, comparator, and various gates. Two
methods can be used to check the circuitry. The prefer­
red method is using Signature Analysis. The other
method checks the AID Digital Circuitry statically. Use
the static method only when a Signature Analyzer is not
available. The preferred method is in the following
paragraph. The static method is in Paragraph 8-8-3 1 .
Do the following:
8-8-29. S A Method.
a. Turn the 34S6A Off.
b. Connect and set-up the Signature Analyzer as
follows (Schematic 8):
A3013I-SRT
Start:
A3013I-STP
Stop:
Clock: A30132-A
Gnd: A3013I-GND
Hold:
Self-Test:
10
c. Move A30J331134
(Schematic 8), as shown in Figure 8-8-2.
d. Turn the 34.56A On.
e. Connect the DATA PROBE of the Signature
Analyzer to A20TP406. Connect one end of a clip lead
to A20TP407. Use the other end of the lead to take
signatures (Schematic 4).
8-8-30. Refer to Table 8-8-1 for the signatures in the
AID Digital Circuitry. To determine the defective IC,
start with the signatures at the output of A20U402.
Determine which ones are wrong. I f for example, only
one signature is wrong, trace it through the various IC's
until a signature is correct. Replace the IC that causes
the bad signature. I f all or most signatures are wrong, it
may be best to half-split the circuitry. In this case, take
the signatures at the output of U404. I f they are good,
the fault is in U40I, U402, or U403. If they are wrong,
U407, U408, or U404 is the cause.
OUI
OUI
the "2" (middle) position
NOTE
Make sure the SA probe shows toggling
when taking the signature at pin 9 of
A20U401.
NOTE
Make sure nothing, except the SA probe, is
connected to the Integrated Circuit on which
the signatures ore token.
8-8·31 . Stalic Method. This method can be used to
check the operation of the AID Digital Circuitry
(5-1,
statically. This is done by manually selling the circuitry
to a certain slope 5-4, etc.) and noting the state of
the Imegrated Circuit under test. The connections used
to set the AID Converter to the various slopes are given
in Table 8-8-2. The state of the Integrated Circuits with
the differem slopes are in Table 8-8-3. Do the follow­
ing:
a. Turn the 34S6A Off.
b. Refer to Table 8-8-2 and connect pins 4, 6, and 8
of A20U408 (or pins 7, 8, and 9 of A20P30) to ground
(use ground 114) or + .5 V, for the desired slope. For ex­
ample, connect all the pins to the 34.56A's + .5 V power
supply to select the AID Autozero Slope (Schematic 4).
c. Refer to Table 8-8-3 for the states of the various
AID Imegrated Circuitry.
d. Turn the 3456A and toggle pin 9 of U401 (momen­
tarily short pin 9 of U401 to ground).
e. Check the states of the Imegrated Circuits.
To prevent damage to the 3456A, always
turn the instrument D j f when reconfiguring
A20U408 to another slope.
NOTE
Toggle pin 9 of A20U401 before checking
the state of A20U401 and U402.
8·B·32. INGUARO LOGIC TROUBLESHOOTING.
8-8·33. The Inguard Logic can cause an Inoperative
AID, Range Failure, or Isolation Logic Failure. I f an
Isolation Logic Failure or Inoperative AID is noted,
make sure the failure is not caused by the Outguard or
AID Circuitry. Go to Paragraph 8-B-6 to determine the
cause of an Isolation Logic Failure and Paragraph
8-8-16 for an Inoperative AID.
paragraphs have the Inguard Logic Failures and
troubleshooting information.
Service
The following
8·B·7