
1.
SECTION 14. INSTALLATION
AND MAINTENANCE
Remove
the 21X
battery base and unplug
the battery from
the 21X. Remove
the four
screws holding
the aluminum cover
plate
and remove
the cover
plate.
Lay the 21X,
panel
down,
on a
padded
flat
surface with
the
circuit cards
up and exposed
as shown
in Figure 14.10-1.
Plug
the battery back
into
the
21X.
Turn on the 21X.
3.
Connect
positive
lead of the frequency
counter to
pin
3 of the integrated
circuit
shown at
Location P10 on Figure 14.10-2.
Connect the
ground
lead
to any
one
of the
capacitor leads
circled
in
the upper left
corner of Figure
14.10-2. Adjust the
variable
capacitor
at
location
516
for
a
period
of
49999.0 microseconds
(20
ppm
fast)
or 50000.0
microseconds
(exactly
on).
Lock
the variable capacitor into
position
wi
a dab of fingernail
polish.
2.
DAC OUTPUT
TEST POINT
(LEFT
SIDE)
DAC OFFSET
POTENTIOMETER
VOLTAGE
REFERENCE
GAIN
POTENTIOMETER
14-8
FIGURE 14.10-1.
Calibration Points for the 21X
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