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Note: Measure all voltages to ground.
50 kc, as indicated by the AN/USM-
(15) If the frequency difference given
in (11) above is greater than that
given in (7) above, adjust C8 coun-
t e r c l o c k w i s e until the vfo fre-
quency is increased by 50 kc, as
indicated by the AN/USM-26. Ad-
just C9 clockwise until the vfo fre-
quency is returned to its nominal
value, 63.000 mc, as indicated by
the AN/USM-26.
(16) Repeat the procedures given in (1)
through (11) above. If necessary,
(4) After the replacement of a faulty
repeat the procedure given in (14)
part, replace the module cover and
or (15) above and the entire align-
perform the alignment procedures
ment procedure until the results
given in d above.
obtained in the procedures given in
(7) and (11) above are within the
prescribed limits.
79. Isolating Trouble in Module A10
(17) Reduce the 721A output to zero and
(fig. 19 and 62)
disconnect it from A9J3. (Allow the
a. Preparation.
ME-26B/U to remain connected to
(1) Prepare the following equipment:
(18) Press switches S2 and S3 (fig. 31)
(a) Frequency Meter, AN/USM-26.
(b) Voltmeter, Meter ME-30A/U.
and note the apc closed-loop volt-
(c) Rf Millivoltmeter 411A.
age as indicated by the ME-26B/U.
(d) Handset H-138/U.
A normal indication is +3.6 volts
dc 0.2.
(e) Resistor, 470-ohm, 1-watt.
(19) Release S2 and S3. Rotate the mc
(f) Multimeter ME-26B/U.
tuning knob from 30.50 mc to 52.50
(g) Rf Wattmeter AN/URM-43A.
mc in 1-mc steps and record the
(2) Set the receiver-transmitter front
apc voltage (indicated by the ME-
panel controls as follows:
26B/U) at each step. The normal
(a) BAND switch at 30-52.
voltage deviation, relative to the
(b) Tuning knobs for 30.00 mc.
indication obtained in the proce-
(c) Function switch at ON.
dure given in (18) above, is approx-
(3) Connect the AN/URM-43A to ANT
imately 0.5 volt.
connector J2.
(20) If the indications obtained above
b. 100-KC Interval Oscillator Test.
a r e not normal, proceed to e
(1) Connect the AN/USM-26, in series
with the 470-ohm resistor, between
(21) If the indications obtained above
test point A10J2 and ground. The
are normal, alignment procedures
AN/USM-26 should indicate 46.850
for A9 are completed.
(2) Connect the 411A between A10J2
e. Faulty Part Isolation.
(1) Remove modules A8 and A20.
and ground. The 411A should indi-
cate 0.2 volt.
(2) Apply an 11.5-mc, 0.68 -voltsignal
(3) Set the receiver-transmitter tun-
between pin 1 of A9J1 and chassis
ing knobs for 30.10 mc. The AN/
USM-26 should indicate 46.950 mc;
(3) Use an ME-26B/U to measure dc
the 411A should indicate 0.2 volt.
voltages at the points listed in the
(4) Set the tuning knobs for 30.20 mc.
chart below. Compare them with
The AN/USM-26 should indicate
the typical voltages listed.

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