Section VI
Paragraphs 6-3 to 6-7
REMEDY
PROBABLE CAUSE
SYMPTOM
See figure 8-3 for location and
1. Attenuator pickup loop broken
Inaccurate R-f output
repair if necessary
loose at ground end
Check and replace if
2. Defective
in,
necessary
attenuator slider
Replace
3. Defective coaxial relay
See Section VIII paragraph
4. MICROVOLTS control knob
improperly set
Check components and
Erratic 90 or 150 cps
Defective Z-1402 or Z-1404 filters
replace where necessary
levels
Replace where necessary
1. C-1405, C-1406, or R-1423
VOR signals inaccurate
defective
See Section VIII paragraph 8-8
2. 30 cps oscillator off frequency
Check tubes, replace if
Defective V-1408B, V-1507, V-1508,
Unable to properly adjust
necessary
or V-1506
90 or 150 cps levels
Replace
R-1479 open
METER reads off-scaleon
CAR position of S-1403
Replace
R-1437, R-1438, R-1492 or R-1493
GS center or 3-db signals
inaccurate after setting
out of tolerance
up TONE LOC
6-6. OSCILLATOR CHECK. The drive on r-f mixer,
6-3. R-F CIRCUIT TROUBLE SHOOTING,
V-1503, comes from both the coarse frequency and
the fine frequency oscillators, While measuring the
6-4. VACUUM TUBE CHECK. If the r-f section is
grid voltage on V-1503, detune the oscillator coils in
inoperative check all tubes. Apply only enough volt-
T-1501 with the tuning wand by inserting the wand into
age to note whether all tubes light. If some do not
L-1511 (figure 8-1). If the coarse frequency oscillator
light turn the power off, locate and replace the de-
is operating satisfactorily the grid drive on V-1503
fective tube.
will fall as T-1501 is detuned. If the coarse frequency
oscillator is not operating properly the tube and relay
K-1501 should be checked before removing the oscil-
lator. The relay can be checked by listening care-
Do not remove tubes when the power is on.
fully while turning the outer knob on the MEGACYCLES
Several tubes are connected in series parallel
control. A click will be heard as the relay opens or
andwithdrawingone may burn out one or more.
c loses each time the frequency is changed. On even
megacycle positions the relay should be energized and
6-5. CIRCUIT ISOLATION. Measure the voltage on
21 volts will appear on terminal #2 of the coarse
standoff E-1508 at the junction of R-1515 and R-1516
frequency oscillator. The switches inside the oscil-
with a 100,000 ohm resistor in series with the probe
later must be oriented properly with the slug table
of a d-c vacuum tube voltmeter. (See grid circuit of
shaft . On the 135.0 mc position one screw on the
V-1506, Figure 9-1. ) This voltage should be greater
than -1.0 volt over the entire frequency range. If
shaft adapter will be approximately straight up and
the other will be on the left side when viewed from
less than -1.0 volt, check the drive on the preceding
the front. (See figure 7-3). The shaft adapter couples
stages. Measure voltages on the grid of each pre-
the slug table to the switches inside the coarse fre-
ceding stage using a 100,000 ohm resistor in series
with the d-c vacuum tube voltmeter and compare with
quency oscillator. If it is necessary to remove the
the typical measurements listed below:
coarse frequency oscillator from the slug table refer
to Section VII, paragraphs 7-2 and 7-3.
TERMINAL
D-C VOLTAGE
TUBE
6-7. Both the coarse and the fine frequency oscil-
lators can be checked by placing the antenna of a
V-1505
Pin #1
-30 v
receiver near the lead on terminal #1 of either oscil-
V-1504
Pin #1
-2.5 v
later and tuning the receiver to the oscillator fre -
V-1503
Pin #1
-2.75v
quency. See tables of oscillator frequencies versus
----
E-1508
-1.4 v
dial positions below:
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