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SERVICING
MODEL 630 POTENTIOMETRIC ELECT&OMETER
4-6.
ZEhXR DIODE REPLACEMENT. Zener diode,
D302, is a reference
for
the voltage
divider,
resistors
R325 to R330.
The values
of resistors
R329 and R330 (Figure
20) are determined
by the reference
voltage
across
diode
D302.
When the zener
is replaced,
the value
of
these
two resistors
may have to be changed.
4-7.
METER ADJUSTMENT.
a.
Potentiometer
R155 (Figure
16) is the internal
meter
sensitivity
adjustment.
It
sets
the current
through
the mater
to indicate
a full-scale
deflection
for
a full-scale
applied
voltage.
b.
Warm up the Model 630 for
30 minutes.
Set the NULL Switch
to the l-volt
range and
set the Reference
Voltage
Dials
to 1.0000.
Adjust
potentiometer
R155 until
the meter
reads
full
scale.
4-8.
ADJUSTING QUADRATURE CONTROL.
a.
Large quadrature
components
in the
null
detector
can cause poor ac rejection,
sluggish
response,
and,
in some cases,
un-
symmetrical
readings
on the most sensitive
ranges.
Use the QUAD ADJ potentiometer,
Rl31
(Figure
16),
to buck out these
compon-
ents when necessary.
While
a large
com-
ponent
is troublesome,
the quadrature
need
not be completely
eliminated.
b.
To adjust
the potentiometer,
set the
Reference
Voltage
Dials
to zero and the
DETECTOR INPUT. Switch
to ZERO CK.
Attach
an oscilloscope
to the junction
of Cl16 and
R134 (from
pin
6 of V1002,
Figure
15).
Ad-
just
potentiometer,
R131, for
the correct
wave form (Figure
9).
FIGURE 9.
Wave Form with
Rl31 Adjusted.
A Type 503 Oscilloscope
was used;
horizon-
tal
sweep was 5 mseclcm;
vertical,
2 v/cm.
20
0166R
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