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MAINTENANCE
MODELS 610B.
6lOBR ELECTROMETERS
FIGURE 18.
Model
610B Internal
Controls.
Test
points
for
the
-LO volt
and
+21 volt
power
supplies
are also
shown.
Refer
to Figure
19 for
the
DC AMP
BAL Control.
a.
Set the
front
panel
controls
to:
METW Switch
Multiplier
Switch
Range Switch
ZERO CHECK Button
FEEDBACK Switch
Zero
the meter
on the 0.1~volt
range.
CENTER ZERO
0.1
VOLTS
LQCK
NORMAL
b.
Connect
the
floating
Model662
across
the
collectors
of transistors
QlO5
and Q106 (this
is
across
the
ends of resistors
Rl81 and R182, Figure
21).
Make
the
connections
from
the
component
side
of the
printed
circuit
board.
Float
the Model
662 ground
terminal.
c.
Adjust
the
DC AMP BAL potentiometer,
R177 (Figure
19))
until
the meter
shows a null.
4-9.
HIGH-MEGOHM RESISTOR VERIFICA!l!ION.
a.
About
every
six
months,
it
is necessary
to check
the value
of
the high-
megobm resistors,
RllO
to R112,
on the Range Switch.
The instrument
should
be
within
its
rated
accuracy
for
two or three
years
from
the
time
It
leaves
the
factory.
After
this,
smne of the
resistors
may drift
cut
of tolerance
and should
be replaced.
Faulty
high-megohm
resistors
will
affect
the accuracies
of measure-
ments
for
the
10-9
to LO-LL AMPERES and the
LOB to 10L2 OHMS settings
of the
Range Switch.
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