TM 11-6625-444-14-2
d. Dc Turnover Adjustment (A7-R91). Ap-
plies to units with serial number 00001A thru
the X10 position and monitor the signal at TP4
as indicated in figure 6-28. (Vertical sensitivity
00010A, 00096A and higher.
will be 200 mV/div. )
(1) Maintain the equipment connections of
the previous adjustment (step b).
(12) Adjust A7-R94 so that the dc level of
the signal displayed on the oscilloscope is be-
tween -500 and -700 mV.
(2) Select the 20 V range and AC + DC
function on the voltmeter.
NOTE
(3) Connect a shorting jumper (B7) be-
tween the front panel HI and LO INPUT
The waveform may contain some
terminals.
component of noise.
(4) Connect the differential voltmeter LO
t e r m i n a l to A7-TP2 and the HI terminal to
A7-TP1.
-.0003 and set its drum dial to 50 (i.e. -350 uV).
(5) Adjust the front panel AC NULL con-
(14) Adjust A7-R144 for zero null meter
trol on the voltmeter for a reading of zero (10
indication (50 uV) on the differential voltme-
uV) on the differential voltmeter.
ter.
from the voltmeter.
f r o m A7-TP5 and connect the oscilloscope
probe in its place. Set switch A7-S17 to the
NORM position.
(7) Adjust A7-R144 for a display reading
on the voltmeter of 0.00000.
(16) Change the oscilloscope volts/div
(8) Remove the shorting jumper from the
switch back to 5 mV/div.
voltmeter INPUT terminals. Disconnect all e-
quipment from the voltmeter.
(17) Adjust A7-R1 13 slowly clockwise un-
til a low frequency oscillation just appears on the
(9) Connect the dc voltage calibrator (A1)
oscilloscope display. Rotate A7-R1 13 counter-
to the voltmeter INPUT terminals. Connect the
clockwise to the point where the oscillation just
plus terminal from the calibrator to the voltmeter
disappears.
HI INPUT terminal and the minus terminal to the
voltmeter LO INPUT terminal. Apply a -10.00
Vdc signal and observe the reading displayed on
(18) Set switch A7-S17 back to the TEST
the voltmeter.
position and reconnect the differential voltmeter
test lead to A7-TP5. Disconnect the oscillo-
scope probe from the test point.
(10) Reverse the connections between the
calibrator and voltmeter. Observe the reading
displayed. Except for the polarity sign, it should
be the same as that observed in step (9). If
+.0002 (i.e. +200 uV). Adjust A7-R144 for zero
necessary, adjust A7R91 until the reading is the
null meter indication (50 uV) on the differen-
same ( 1 count).
tial voltmeter.
(11) Reverse the connections between the
(20) Switch A7-S17 back to the NORM
calibrator and voltmeter. Decrease the output
position. The differential voltmeter null reading
signal from the calibrator to -0.1 volt. Observe
should remain unchanged (50 uV).
6-54
