Ratio Failure; Analog Filter Failure - HP 3456A Operating And Service Manual

Digital voltmeter
Hide thumbs Also See for 3456A:
Table of Contents

Advertisement

Model 3456A
e. If the voltage is noisy, A2OQ3 1O, Q3 1 1 , and
associated circuitry is noisy.
f. If the voltage is steady and quiet, measure the
voltage at pin 6 of U307. The voltage should be a solid
5 V «
50 p.V change). If good, replace U308. If noisy,
replace U307.
8·C·52. RATIO FAILURE.
S . C·53. A Ratio measurement is a multiple measure­
ment which uses the DCV and ACV measurement cir­
cuitry (dependent on the selected Ratio Function).
Because of this, make sure both functions are working
correctly, before troubleshooting any Ratio Failures.
Go to this Service Group for any DCV Failures and Ser­
vice Group E for any ACV Failures.
8-C-54. If the DCV and ACV Functions are good, the
only olher components that can cause an inoperative
Ratio, are some of the Input Switching FETs. Since the
FETs used in Ratio are also used in the 4-WRO Func­
tion, make sure the function is good. Do the following:
a. Press the 3456A's RESET button.
b. Set the instrument to the 4·WRO Function and the
K ohm Range.
c. Connect an accurate
to the Input Terminals (VOLTS and 4WRO SENSE). If
an accurate resistor is not available, use one of which
the exact value is known.
d. If the Ohms Function fails, go to Service Group D
for troubleshooting.
e. If the Ohms Function is good, replace A2OQ1 15,
Q1I6.
.00 1 0]0) 1000 ohm resistor
( ±
8·C·55. ANALOG filTER FAILURE.
8-C-56. To determine if the Analog Filter fails, do the
following:
a. If the Analog Filter is inoperative in only the
100 mY, I V, and 10 V Ranges, make sure A20Q I 1 4 is
on (when the Filter is on).
b. If the Filter is inoperative in only the lOO and 1000
V Ranges, make sure QlOt is on (when the Filter is on).
c. If the Filter is inoperative in all Ranges, press the
3456A's RESET button.
d. Set the instrument to the I V Range.
e. Apply a I V at 50 Hz Sine Wave to the VOLTS
put Terminals.
f. Connect the low input of an AC Voltmeter
3456A's High Input Terminal and the low input of the
meter to the source of A20Q I 1 6 (junction of Q1 16,
Q1 18, and QI 19).
g. If the reading on the Test Voltmeter is approx·
imately I V ac (RMS), the Analog Filter is working cor·
rectly.
h. If nOI, make sure QI21 and QI t I are off, when
the Filter is on. Also make sure capacitor CI05, CI06,
and CI07 are not shorled or open. Use an ohmmeter
check for shorts. An open capacitor can be checked by
connecting the same value capacitor across
suspected open capacitor, while monitoring the ac
voltage across RIOI, RI09, K103, R t JO, and R120.
Replace U105 if everything appears good.
Service
in­
10
the
10
the
8-C-9/8-C- J O

Hide quick links:

Advertisement

Table of Contents
loading

Table of Contents