100V Adjustment - HP 3456A Operating And Service Manual

Service
8·F· 18. DCV Adjustmont.
8·F·19. Do this procedure only after repairing the Input
Amplifier and Input Switching Circuitry. Do the follow·
ing:
a. Make sure the 3456A has been warmed up for at
least 1.5 hours, then press the instrument's RESET but·
ton.
b . Connect the input of the Input Amplifier (white
wire connected to pin 3 of A2OQ31O) to A2QTP 102.
c. Set jumper A20J29 to the ground position, as
shown below.
us oo
d. Set the 3456A to the lOOmV Range and the 6 Digit
Mode (by storing 6 into the N DIGIT DISP Register).
e. Connect a high impedance Digital Voltmeter (like
the 3456A) to A20TP303. Adjust A20R334 until a null
(0 reading, ± lOmV) is read on the test meter. Remove
the meter from TP303.
f. Reconnect the input of the Input Amplifier to
A20Jl9.
g. Replace jumper A20J29 to the RUN position.
h. Short the 3456A's VOLTS Input Terminals.
i. Note the instrument's displayed offset reading.
j . If the offset is zero, continue with step m.
k. If the offset is positive or negative by less than 2iJ. V
(20 counts), the 3456A's low input circuitry needs to be
padded. The padding instructions are as follows:
1 . If the offset is positive, connect a resistor (see step
3 for the correct vlue) between the
at A20CR102 and the node between A20R149 and
A20RI04.
2. If the offset is negative, connect a resistor (see step
3 for the correct value) between the - 1 3V ter·
minal
at A2OCRI02 and the
A20R149 and A20RI04.
3. The correct resistor values are as follows:
Offset
PaddIng Resistor
0.0-0.9.V no resistor required
1.0-1 .4.V
12M ohm
1.5-1.9.V 8.2M ohm
2.0.V
6.8M ohm
I. If the offset is > 2iJ.V, calibrate and/or repair the
instrument.
m. Check the 3456A's IOOV Range for a maximum
offset of 0.2mV. If the offset is greater, calibrate
and/or repair the instrument.
n. Set the 3456A to the 100MV Range.
o. Set the 3456A to the 100 Number of Cycles In·
B
8-F-4 Rev
o
z
z
il
Cl
!2::2l
o
J2 9
0 0 0
+
13V terminal
node between
hp
Part Number
· ·
0699-0740
0699-074 1
0698-6592
tegrated Mode (by storing 100 into the N CYC INT
Register).
p. Adjust A20R 147 for a zero reading
the display.
q. Turn the Analog Filter on (press the FILTER but­
ton) and adjust A20R148 for a zero reading ( ± 2 counts)
on the display.
r. Remove the short from the Input Terminals.
H·20. IOOV Adjustment.
8·F-21 . Do this procedure only when the 100V Adjust·
ment (Front Panel Adjustment Pot "E") is out of ad­
justment range. If that is the case, remove (or insert)
jumper A20JMPR602 to bring the adjustment into
range.
8·F·22. Ohms Adjustmont.
8-F-23. Do this procedure only after repairing the
Ohms Current Source. Do the following:
a. Press the 3456A's RESET button.
b. Set the instrument to the 4-WRO Function and the
6 Digit Mode (by storing 6 into the N DIGIT DISP
Register).
c. Remove the 3456A's Front Panel Calibration
Cover (see Section V, Paragraph 5·9 for the cover's
removal procedure).
d. Turn the front panel Calibration Pot "F" corn·
pletely counter-clockwise.
e. Connect an accurate IOK ohm Resistor (its value
within the 3456A's IOK ohm specifications) to the 4-WR
Ohms Input Terminals.
f. Note the front panel reading. The reading should
be between 9.9970K and 9.9990 K ohms. If the reading
is good, no adjustment is needed. If the reading is not
within the limits, do the following:
1 . Turn the 3456A Off.
2. Replace and make sure jumpers A20JMPR201
through JMPR204 are in their respective places
(replace with new jumpers, if missing).
3 . Turn the 3456A On and allow the instrument to
warm up to its operating temperature.
4. Set the instrument to the 4-WRO Function and the
6 Digit Mode (by storing 6 into the N DIGIT DISP
Register).
5. Reconnect the accurate lOK ohm Resistor to the
4-WR Ohms Input Terminals.
6. Note the front panel reading. Each one of jumper
JMPR201 through JMPR204, when cut or re·
moved, changes the reading a certain amount. To
bring the reading into tolerance, determine the
needed resistance value. Once that is determined,
remove one or more jumpers to bring the reading
Model 3456A
( ±
1 count) on