HP 3465B - Page 53

Section VII
Model 3465B
a. Apply + 1 V dc to the input on the 2 V dc range.
Check the waveform at jumper A. An easy access point is
the proper end of €19. The signal should appear as shown
below.
I 2V TO 2,5V
b. The signal at the base of Q9 should appear as
follows.
OV-
• 0,4« »
■7V-
c. The signal at the COMPTP test point should appear
follows.
OV-
» - IV-
« 0,4i »
«5 2,5V-
d. The signal at AZTP should be the following.
OV —
*-IV-
1^0,21-^
e. The switching of the Auto Zero circuit controls the
pulsing of the A/D loop. If it is malfunctioning, check the
IZ signal from the Control State Decode, Q1 and Q2.
NOTE
If the IZ signal and Auto Zero circuit are
proper, troubleshoot the circuit immediately
before an improper waveform is detected.
f. Short point RS to ground.
g. Measure the voltage at AZTP. If the voltage is about
- 1 V, the fault is probably in the Reference Supply, if not,
the fault is within the loop.
h. Place the instrument in any ohms range and apply
- 7 volts at the junction of R56 and R57. (The internal
supply may be used.) The voltage at jumper A should now
be about + 9.5 volts, the voltage at COMPTP should be near
zero, and the voltage at the COMP terminal should be about
- 1 volt.
1. Now apply +10 volts at the R56/R57 junction and
the respective measured voltages should be about - 6.5,
- 2, and - 6.
NOTE
If any of the test voltages are incorrect, trouble-
shoot the circuit immediately forward of the
first bad reading. If all voltages test good, the
fault is probably in the Auto Zero Circuit.
7-31. Digital Troubleshooting.
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KAUTION4
This instrument contains CMOS digital IC's
and, therefore, is highly susceptible to failure
due to static discharge. Extra handling precau
tions should be used when servicing circuit
areas containing these devices.
7-32. Reiterating the test of the general section short pin 7
of J1 to test point C with the instrument in the 1 VDC
range. Observing the display, if + 1.0000 is not indicated,
the logic or display is at fault.
7-33. Display and Display Driver Verification.
7-34. There are two display driver and display verifica
tion tests that can be performed. One can be implemented
from the A1 board as a quick check and the other can be
used for troubleshooting and is accessed from the A2 dis
play interface board. For both tests, place the ANALOG/
DIGITAL ISOLATION JUMPER connection between test
points CP and PL with FUNCTION and RANGE settings at
DCV and 200 m respectively.
7-35. Display and Display Driver Quick Test.
7-36. This verification test is a quick method to test the
display and display driver and is implemented from the A1
board.
a. Apply - 7 V to the test point pad DT on the A1
board.
b. Verify the display indication as illustrated below
with plus/minus indicator alternating.
i LI U U U
U.LI U
7-4