TM 11-5826-225-35
Input column. These voltages in the Input
190- to 400-kc range and tune to
column are the signal voltage required to ob-
200 kc. Set BFOOFF switch to
tain an indication of 5 volts dc on the vtvm. If
BFO and adjust signal generator
the voltage differ abnormally, check the IF
for zero beat. Then set BFO--OFF
t r a n s f o r m e r s and if necessary, use further
switch to OFF
isolating techniques (para 28) to determine
(c) Connect vtvm to cathode of audio
detector CR1. Ground agc testpoint
the defective component.
TP3.
Adjust signal generator output level
to produce an indication of 5 volts
dc on the vtvm. Record the signal
generator output voltage required
to produce the vtvm reading of 5
volts d c .
Determine mixer gain by dividing
the signal generator voltage applied
to the base of Q7, to produce 5 volts
dc on the vtvm as in d above, by the
value obtained in (d) above.
Typical mixer gain values at various
frequencies are listed in the follow-
ing chart. Repeat the above proce-
dures for the remaining frequencies
listed in the Frequency column. If
mixer gain differs appreciably from
agc testpoint TP3 and turn variable resistor
t h e chart, use further isolating
R90 fully clockwise. Set vtvm for measuring
techniques (para 28) to isolate the
dc voltages from O to 5 volts. Connect positive
defective component. After these
test lead to cathode of audio detector CR1 (fig. 2-14 o r
tests, remove the agc ground con-
2-14.1) and negative test lead to receiver chassis.
nection and adjust R90 (para 317).
Set test set and control unit controls as out-
lined in paragraph 26b(1). Set RF signal
generator output signal to 142.5 kc modulated
30 percent at 400 cps. Adjust output level to 6
or 7 microvolt and apply signal to the base of
output signal until vtvm indicates 5 volts dc.
The signal generator output signal required to
produce this de voltage level should be in the
range of 6.5 to 7 microvolt. Record this refer-
ence level for use in the following tests. Remove
signal generator and vtvm connections.
(2) Gain of mixer at RF frequencies.
(1) Gain of mixer at IF frequency.
(a) Turn variable resistor R90 fully
clockwise. Ground test point TP--3.
(a) With signal generator set as shown
(b) Set RF signal generator for a 200-
above, use the 50-ohm probe and
kc output signal at a level of 6 or 7
apply 142.5-kc RF signal to the
m i c r o v o l t . Using 50-ohm probe,
junction of C29 and contact 3 of
apply signal to the junction of C29
front switch wafer S11 labeled
and contact 3 of front switch wafer
TP4 in figure 5-10 or 5-10.1.
S1-I labeled TP-4 in figure 5-10
(b) Set control unit range switch to the
or 5-10.1.
2-26 C h a n g e 1
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