TM 11-6625-486-14&P
(2) Turn the vtvm FUNCTION to AC and the
a. Tracing Crystal Oscillator Signal.
When
RANGE to 10V. Connect the ac probe ground clip to
performing this procedure, use the vtvm rf probe and
the meter chassis and hold the probe tip on the collector
the test setup shown in figure 6-7. Locate test points
of Q101.
TP201 and TP202 on the crystal oscillator circuit board
(3) Turn the frequency meter FUNCTION SW
to OPER. Take one voltage measurement with the
(1) Turn the vtvm FUNCTION to AC and
RANGE SW on A and the other on B. The vtvm should
RANGE to IV.
indicate 4 volts for range A and 4.1 volts for rangel B.
(2) Connect the vtvm ac probe ground clip to
Rotate the frequency meter TUNING control and note
a convenient point on the frequency meter chassis.
that the output signal varies with the frequency.
Hold the ac probe tip on test point TP202 (fig. 6-7).
(4) Turn the vtvm RANGE to 1V. Touch the
CAUTION
probe tip to the collector of Q102. The vtvm should
Do not let the probe tip come in
indicate 0.14 volt on range A of the frequency meter and
contact with any other circuit board
0.3 volt on range B.
connection.
(5) A relative signal tracing check of vfo
(3) While holding the ac probe on test point
output signal can also be made at the collector of mixer
TP202, turn the frequency meter FUNCTION SW to
Q301.
The collector soldered connection can be
CHK and the RANGE SW to A. If the 1-MHz output
reached through the right sideplate cotout of the
signal measured at this point does not agree with that
frequency meter chassis (fig. 6-2).
shown in figure 6-7, troubleshooting is required. The
signal on TP202 is the buffer output of Q202.
(6) The ac signal at, this point, for the same
vfo frequencies given in (1) through (5) above, should
(4) To measure the emitter-follower output
be approximately 2.4 volts on range A and 0.88 volt on
signal of oscillator Q201, touch the probe tip to test point
range B.
TP201. If signal voltage does not agree with figure 6-7,
transistor Q201 is not oscillating properly.
c. Signal Tracing High Frequency Vfo Signal. This
circuit has no test points for signal tracing but its activity
(5) To measure the 2.5-MHz output signal,
can be checked as follows:
turn the frequency meter FUNCTION SW to CHK and
the RANGE WS to C. Touch the ac probe tip to test
(1) In the high frequency fvo circuit (fig. FO-
points TP201 and TP202.
2 (2) or FO-3 (2)), locate the collector connection of
oscillator Q1.
(6) The absence of a signal at TP201 for both
the 1-MHz and the 2.5-MHz crystal frequencies
(2) Turn the vtvm FUNCTION to AC and the
indicates that Q201 is not oscillating because of a
RANGE to 1V. Connect the ac probe ground clip to the
defective transistor or circuit component. No output
vfo side panel chassis ground. Touch the ac probe tip
signal at either the 1-MHz (ranges A or B) or the 2.5-
to the collector of Q1 or the junction connection of L1
MHz (range C) frequencies would indicate a defective
and C702B.
crystal. The presence of a signal on TP201 and
(3) Turn the frequency meter FUNCTION SW
absence of a signal on TP202 indicates trouble in buffer
to OPER and the RANGE SW to C. Set the frequency
stage Q202.
meter dial to 65 MHz. With this frequency, the vtvm
b. Signal Tracing Low Frequency Vfo Signal. This
should indicate 0.26 volt.
circuit has no test points for signal tracing but its activity
(4) The buffer output signal of Q2 must be
can be checked as follows:
measured at test point TP301 on the mixer circuit board
(1) On the low frequency vfo circuit board
(fig. FO-2 (1) or FO-3 (1) ). At TP301, the signal should
(fig. FO-2 (2) or FO-3 (2) and 6-24 or 6-25) locate the
be 0.16 volt.
collector connections of Q101 and Q102. Transistor
NOTE
Q101 is the oscillator and Q102 the buffer.
The above signal values will
gradually decrease with increasing
frequency.
6-15
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