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f.
Set the meter switch to ZERO CENTER.
g.
Check that the NULL INDICATOR pointer is at the midscale
increment.
If necessary, adjust the C ZERO FINE control to
center the pointer.
h.
Turn the CONDUCTANCE control to minus 100 pmhos on the
G-scale dial.
i.
Loosen the locking nut on LI04 by turning ccw.
j„
Carefully adjust LI04 until the NULL INDICATOR pointer is at the
midscale increment, * 1 subdivision,
k.
Carefully tighten the L104 locking nut by turning cw.
4.10
BRIDGE-ASSEMBLY CAPACITANCE ALIGNMENT AND CALIBRATION.
a.
The following procedures align or calibrate the capacitive elements in the
bridge assembly.
The procedure in paragraph c, however, is a calibration
check of the CAPACITANCE control on the 1 multiplier range rather than a
calibration adjustment.
Calibration at the 1 multiplier range is beyond the
capability of the user since it involves special-purpose equipment and
highly specialized techniques.
NOTE:
Do NOT perform any procedure except paragraph c
unless authorization is given by the Boonton
Electronics Corporation.
If the seals on the bridge
assembly are broken or removed without authorization,
the Model 75D warranty is null and void.
b.
C ZERO Control Alignment (C505).
1.
Remove the Model 75D cabinet (par. 4.12).
2.
Remove the bridge assembly cover plate (par. 4.13).
3.
Adjust the Model 75D front panel controls in accordance with Table 4.
4.
Set the MULTIPLY C switch to 0.0001.
5.
Zero balance the bridge as described in paragraph 3.5.
6.
Set the MULTIPLY C switch to 1 .
(Do not zero-balance the bridge.)
7.
Adjust C505 for a maximim dip of the NULL INDICATOR pointer.
The pointer does not have to dip to zero, but it must be in the LO
sector of the meter scale; if necessary, fine-trim the 12 o'clock
position of the R/G ZERO control.
75D
b-370
65
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