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Table
5-8.
DC
Attenuation
and Chopper
Amplifier
Checks
Step
Item/Component
Required Condition
Remarks
1
Turn on power.
Select
20mVDC
range.
Short
input
and
adjust
F.P.
Zero
for
±
.0000
on
display.
NOTE:
Insufficient
zero
adjustment
may
indicated
leaky
FET
switches
in
Chopper
Amplifier
Circuit.
2
TP5,
TP6*
=
-7.5V
DC
(on
DMM).
Chopper
Drive.
Signals are
actually
0
to -15
square
waves
at
390Hz.
A
steady
zero
volt
or
-15V
signal
indicates
a
problem
in
the
chopper
drive or
clock
circuitry.
3
External voltage
source.
Apply
+
19mV.
Calibrated input.
4
R143
(yellow
wire
slide)*.
+
19mV.
Input to
chopper
amplifier
H-
1
attenuation (range
resistors).
5
7P1*
+
1.9V
Input to
U106, chopper
output
(
X 100
gain).
6
E>^ternal
voltage
source.
Select
200mVDC
range. Apply.
+
190mV.
Calibrated
input.
7
R143
-H
190mV
Input to
chopper
amplifier
-^1
attenuation.
8
TP1
+
1.9V
Input to
U106, chopper
output
(
X
10
gain).
9
External voltage
source.
Select
2VDC
range.
Apply
+
1.9V.
Calibrated input.
10
R143,
TP1
+
1.9V
-i-
1
attenuation,
x
1
chop-
per
gain.
11
External
voltage
source.
Select
20VDC
range.
Apply
-H19V.
Calibrated
input.
12
R143
+
1.9V
10 attenuation (range
resistors).
13
External voltage
source.
Select
200VDC
range.
Apply
+
190V.
Calibrated
input.
14
R143
-h1.9V
-5-
100
attenuation (range
resistore).
15
External
voltage
source.
Select
1000V
(1200V)
DC
range.
Apply
+
1000V.
Calibrated
input.
16
R143
+
1V
+
1000
attenuation (range
resistors).
*0n
main
printed
circuit
board, see Figure
5-1.
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