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Page Title:
Main unit, with tuning unit 1 interconnected by test harness (fig. 46). (cont) |
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|  Probable
trouble
Symptom
Correction
Step
Disconnect operating power; use
7
Meter cannot be zeroed with con-
Open or shorted ZERO ADJ vari-
ohmmeter to check resistance of
able resistor R715 (fig. 52).
trol switch at ZERO ADJ.
R715, and replace if defective.
Check L701 for continuity; replace
Open rf choke L701 in filter box
if open circuited.
assembly (fig. 45).
Check for infinite resistance from
Shorted feedthru capacitor C741
protruding terminal of C741 to
chassis ground. Remove cause of
power to if. amplifier bias
grounding center conductor of
circuit.
f e e d t h r u capacitor.
Check for -150 volts dc from termi-
Section W of switch S702 not sup-
nal 1 of filter box assembly (fig.
plying -150-volt potential to
terminal 1 of connector J701
repair S702 section W, or replace
defective switch.
Use ohmmeter to check resistance
8
O p e n meter multiplier resistor
Meter indications are present with
of R724, and replace if open.
R725 (fig. 53).
function switch at CW AVERAGE,
Terminals 3 and 4 of S702 (fig.
Clean and repair S702, section X
CW PEAK, and METERED
(rear), or replace defective
SLIDEBACK, but not at PULSE
switch.
ing required contact.
PEA K.
Use ohmmeter to check resistances
Open resistor R709 and/or R710
9
Meter indications are present with
of R709 and R710; replace defec-
function switch at CW AVERAGE,
tive component.
CW PEAK, and PULSE PEAK,
Check L702 for continuity; replace
Open rf choke L702 in filter box
but not at METERED SLIDE-
assembly (fig. 45).
if open circuited.
BACK.
Shorted feedthru capacitor C742
Check for infinite resistance from
protruding terminal of C742 to
chassis ground. Remove cause
developed across voltage di-
v i d e r resistor R709.
of grounding center conductor of
feedthru
capacitor.
Low plate or screen grid voltage
Check all plate and screen grid
10
Turn IMPULSE GENERATOR DB
i n amplifier, mixer, and/or
ABOVE lV/MC switch at OFF.
ble for tuning unit in use). Locate
With headset plugged into front-
oscillator stage of tuning unit.
defective plate and/or screen
panel PHONES jack, and GAIN
control rotated fully clockwise,
r e s i s t o r , and/or bypass capaci-
tor. Replace defective part.
hissing noise cannot be moni-
Rf or if. circuits not properly
Refer to paragraphs 84 through 87
tored in headset.
aligned.
for rf and if. alignment proced-
ures.
11
Same as 10 above except that, with
Poor shielding or interstage cou-
Ground the grid of each stage, one
pling, or poor ground connec-
GAIN control at midposition,
at a time, through 0. l-uf capaci-
oscillation (indicated by whistle
tions to chassis.
tor; work from rf input to if. out-
or howl) is heard in headset.
put until grounding one particular
stage causes oscillations (whistle
or bowl) to ease. Trouble is
localized to that stage of which
g r o u n d grid caused end of oscil-
lations, or in prececding stage or
stages.
110
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