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|  Correction
Probable
trouble
Symptom
Step
voltage is indicated, check rf
choke L522 for open circuit. If
this does not remedy trouble,
suspect defective contacts 1 and
wiper (W) on front section of
switch S502 (fig. 72). Repair or
replace defective switch.
Lack of -150-volt power source
Check for B- voltage to rf amplifier
J501 by measuring voltage from
to plate circuit of rf amplifier
protruding terminal of feedthru
capacitor C505 (fig. 74) to chas-
sis ground. Proper voltage will
be somewhat less than 150 volts,
depending on setting of V501
ADJ control R503 (fig. 72). No
voltage at C505 indicates defec-
t i v e variable resistor R503, rf
choke L504, and or a defect in
wire lead which is soldered to
high-potential terminal of V503
ADJ control R508 (fig. 72).
Replace defective component and/
or repair wire lead connection.
Lack of heater power at pin 1 of
Check rf choke L506 (A, fig. 74)
which is tied between tube clip at
oscillator tube V502 (fig. 50).
rear of V502 cavity and feedthru
capacitor C512. In unsoldering
or soldering L506 from tube clip,
use pair of pliers on resistor
axial lead as heat sink to avoid
damage to acorn-type electron
tube V502. Unsolder and resolder
quickly; keep pliers on axial lead
for approximately 1 minute after
removing soldering iron, to dis-
sipate heat.
With power removed, check rf
Lack of plate potential at pin 4 of
choke L508, feedthru capacitor
Oscillator V502 (fig, 50).
C509 and/or resistor R505 (A,
Check bypass capacitor C514, feed-
Lack of 6.3-volt heater power at
thru capacitor C502, and rf
protruding heater terminal (fig.
choke L502. Replace defective
part.
Check R502 and capacitor C503 (A,
Lack of anode potential at rf
amplifier V501 (fig. 50).
Replace with crystal diode known
Defective crystal mixer CR501
to be in satisfactory operating
(A, fig. 74).
condition.
Same as for tuning unit 2, step 2.
4
Defective relay K2 or resistors
Meter indications are present when
If. step attenuators are identical
R1 through R5 in if. step
SIGNAL ATTENUATOR DB
and interchangeable in tuning
attenuator AT501 (fig. 66).
switch is rotated to 0 SUBST.
units 2, 3, and 4.
ONLY, but pointer cannot be
With operating power removed,
zeroed at 20, 40, 60, and 80,
check precision resistors R1
even with GAIN control set fully
through R5 (1% tolerance) for
clockwise.
values indicated on schematic
diagram (fig. 25). Replace defec-
tive components.
With SIGNAL ATTENUATOR DB
Defective-relay K1 in if. step
Meter indications are present when
switch at 40, 60, or 80, check for
attenuator AT501 (fig. 66).
SIGNAL ATTENUATOR DB
-150-volt energizing potential
switch is rotated to 0 SUBST.
from protruding terminal of feed-
ONLY and to 20, but pointer cann-
thru capacitor C1 to chassis
ot be zeroed at 40, 60, and 80.
ground. If no voltage is present,
relay K1 will be inoperative.
144
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