TM 11-6625-486-14&P
Table 6-3. Troubleshooting- Continued
Malfunction
Probable Cause
Corrective Action
12. Little or no harmonic output
Replace CR301.
signals at ANT. jack.
mixer circuit.
13. No frequency meter output signal
No voltage on vfo circuit.
With vtvm, measure dc voltage at
at ANT. jack when FUNCTION
the junction of R5, C8 and L2.
SW set to OPER, and RANGE SW
Capacitor C8 shorted.
Replace C8.
is in C position.
Capacitor C10 shorted.
Replace C10.
No voltage from power supply.
Check voltage from TP604.
Incorrect voltage on buffer stage Q2.
With figure FO-2 or FO-3, check
voltage on Q2. If voltages do not
agree, turn power off and make
forward and reverse resistance
measurements. Replace Q2 if
necessary .
Incorrect voltages on oscillator stage
Make voltage and resistance
Q1.
Measurements and replace QI if
necessary; then adjust R4.
No rf signal on base of Q2.
Perform the signal tracing procedure
Transistor Q1 not oscillating.
Pay particular attention to the
voltages on the emitter and base of
Q1. If these voltages vary over 5
percent from figure FO-2 or FO-3,
adjust R4. If correct voltages
cannot be obtained, replace Q1.
R3 or R6 defective.
Replace R3 or R6.
14. Little or no harmonic output
Harmonic generating diode CR303 or
Replace CR303.
signals at ANT. jack.
C304 in mixer circuit.
15. With FUNCTION SW set to
Headset defective.
Check headset.
CHK, and RANGE SW in any
Audio amplifier circuit defective.
Refer to steps 22 and 23 below.
position, no beat notes can be heard
Mixer circuit.
Refer to steps 18 through 21 below.
in frequency meter headset.
Function switch S701 not making
Check continuity through S701 and
contact.
replace switch if necessary.
No voltage from power supply.
Check for presence of voltage at
TP603 on power supply circuit
board (fig. FO-2 or FO-3).
Capacitor C206 shorted.
Replace C206.
Incorrect or no voltages on buffer
Check voltages on base, collector, and
stage Q202.
emitter of Q202. With power off,
make resistance measurements and
replace Q202 if necessary.
Incorrect or no voltages on oscillator
Check voltages on base, collector, and
stage Q201.
emitter of Q201. If there is no
voltage on the collector of Q201,
turn power off and check resistance
of L201 and L202 (table 6-2).
Replace coil if necessary.
16. With FUNCTION SW set to
1-MHz crystl1-MHz crystal Y202
Replace crystal. Adjust 1-MHz
CHK, and RANGE SW in either A
defective.
frequency (para 6-26).
or B position, no beat notes can be
Capacitor C202 or C203 defective.
Replace C203.
obtained.
Low frequency to vfo inoperative.
Refer to steps 7, 8, and 9 above.
17. With FUNCTION SW set to
2.5-MHz crystal Y201 defective.
Replace crystal. Adjust 2.5-MHz
CHK, and RANGE SW in C
frequency (para 6-26).
position, no beat notes can be
Capacitor C202 or C203 defective.
Replace C202.
obtained.
High frequency vfo inoperative.
Refer to step 13 above.
18. With FUNCTION SW set to
Headset defective.
Check headset and wiring.
CHK and RANGE SW in any
Audio amplifier.
Refer to steps 22 and 23 below.
range, no beat notes can be heard
Crystal oscillator.
Refer to steps 15 through 17 above.
in meter headset.
No voltage on mixer circuit.
With vtvm, check voltage on test
point TP303 (table 6-1). Voltage
should agree with diagram.
Check voltage on TP603 on power
supply circuit board (table 6-1).
Capacitor C303.
If shorted, replace.
Incorrect or no voltages on Q391.
Check voltages on base and collector
of Q301. Replace Q301 if necessary.
6-10
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