Operating instructions

Symptom
Probable
trouble
Correction
No output signal
heard
as
B.F.O.
trim-
mer
is rotated
and a 455-kc, 400-
cycle modulated
signal is
connected
through
a .05-pf capacitor
to
pin
6
of
V3, and PHN.-C.W.-NET-CAL.
switch 52
turned
to C.W.
position,
after
previous
checks
have been
made.
No output
signal
is heard,
r.vith PHN.-
C.W.-NET-CAL.
srvitch
52 set to
CAL.
position
as tuning
capacitor
is
varied,
after
previous
checks have
been made,
Defective
bfo
stage. Defective
tube
V7.
Open transformer
T13.
Defective
crystal
calibration
tube,
crystal, or
circuit.
Check tube
V7 and replace
if defec-
tive.
Replace
or repair
trans-
folmer.
Use signal
substitution
test in
paragraph
81
to
localize
tlouble.
Check
tube \r5
and
crystal;
replace
if
defective.
Chech resistors
R13
and R14,
capacitors
C25
and C26,
and
transformet:
TL2; replace.
Use
signal
substitution
test
(par.
81)
to localize
trouble.
b. Localizing
Trotúle,
Symptonr
Probable
trouble
Correction
Receiver
inoperative
r,vith
OUTPUT
HIGH-LOW
switch 54
set to HIGH
position.
Receiver inoperative
with
OUTPUT
HIGH-LOW
srvitch 54
set to LOW
position
after
previous
checks have
been made.
Oscillation
(indicated
by
whistle or
howl).
Reception
distorted;
objectionable
hrrn in nrrfnrrt
Noisy.
fading,
or weak
r.eception.
Intermittent noise.
Defective
a-f
stage
or screen
voltage
fective
speaker.
Defective
tube
V7
stage.
Defective
tube,
poor
high-resistance
solder
chassis,
V6 or
V8. No
plate
at
VG
or
V8.
De-
or defective a-f
shielding, or
connection
to
Check tubes
V6 and
V8.
Use
signal
substitution
(par.
80)
to
check
each
stage. Repair
or replace
de-
fective component.
Use signal substitution
(par.
80) to
check
a-f stage. Repair
or replace
defective component.
Check tubes.
Check
rviring
to
ground
solder
points.
Use signal substi-
tution
tests
(pars.
80
through 84)
to localize
trouble.
Repair or re-
place
defective
part.
To
check
grid
circuits, measure
re-
sistances
to locate faulty
compo-
nents.
Replace faulty
components.
Check wiping
contact on
A.F.
GAIN
and R.F.
GAIN controls.
Check
avc circuit.
Check antenna
instal-
lation for
poor
connections.
Use
signal
substitution
tests
(par.
80
through 84)
to
localize
trouble.
With an insulated
prod,
gently
tap
and slightly
move
all
tubes, resis-
tors, and capacitors
to
locate
loose
elements
or loose
connections,
Use
signal
substitution
tests
(pars.
80
through
84)
to localize
trouble.
Repair
or
replace
defective
part.
Open
grid
resistor
or leaky
capacitor
in audio
circuits.
Open capacitor in
the
power
supply filter
circuit.
Faulty gain
control.
Defective
avc
circuit.
Faulty
antenna,
Defective
tube,
resistor,
or capacitor.
79.
Generol
Signol Substitution
Notes
o.
Signal
substitution
requires
a source of
rndio, i-f,
and r-f signals. A
headset
or the
,udspeaker
also
is required.
b. Note
the volume. and listen
for
serious
62
distortion
from
the loudspeaker
or headset
at
the
various
points
in
the signal
substitution
procedure.
When
possible,
compare
operation
rvith
a receiver
known
to be in
good
condition.
c.
Check
the wiring
and
soldering
in
each
stage
during
the
procedure.
AGO 3T3A