No Transmission; No Am Modulation; No Noise Blanker Operates; No Led Channel Indicator Lights - Realistic TRC-449 Service Manual

C) If a RF voltage of 20 mV/P-P or more at the
base and 300 m V /P-P or more at the collector
of the 7.8 MHz AMP (TR7), the 7.8 MHz
AM P is all right.
If no R F voltage is present at the base, check
D7 and D35 circuits.
D) If a RF voltage of 34 MHz, 2 V /P-P or more
is readable at the first gate of the mixer
(FET7) no problem should be expected with
Local Oscillator.
E) Check DC and RF voltages of each of the
following circuits: TR43, TR44, TR45, FET6
and 'FET7 (in this order).
F) If voltages do not appear at the collector of
TR43 or TR44, check the regulators (TR25
or TR26). If the regulator has a DC output of
approx. 5 to 7 V. the regulator should be all
right.
NO TRANSMISSION
(SSB)
A) If AM transmit and modulation are working
properly, the problem is in the circuit of 7.8
MHz AMP (TR6) or in the circuit of Balanced
Modulator (IC2) or in the Microphone AMP
(TR 16). .
If no RF voltage of 7.8 MHz, 50 mV /P-P
appears at pin 8 of IC2, check circuits from
TR28 to pin 8 of IC2.
If no audio signal of approx. 70 mV/rms
appears at pin 1 of IC2 under modulation,
check circuits before TR 16.
B) If the voltage reading at pin 8 and pin 1 of
IC2 are correct then problems are with TR6
bias circuit or D6.
C) If the output of TR6 is produced properly
check item D) and E) of NO TRANSMIT
(AM) above.
NO AM MODULATION
The signal in the modulation circuit flows
through IC3 - D22 - D21 - TR20 - TR22 - IC4.
Therefore check to determine at what stage this
signal ceases (to isolate a defective part). If no
signal appears at pin 2 of IC3, it is probable that
there is a short circuit between the collector and
emitter of the clamping transistor (TR 18) or
between the collector and emitter of the TR 19.
NO NOISE BLANKER OPERATES
A) If the RF output voltage of TP-5 is 100 mV
or less with Noise Blanker ON, when signal of
23.5 MHz 200 J1V carrier is applied to
antenna, check the RF AMP circuits (lC1)
and L 1 and L2.
B) If a pulse noise is amplified to 0.7 V/P-P or
more at the base of TR3 when an ignition
noise (or pulse noise) of 100 mV/P-P or more
is applied to the antenna, the circuits of TR 1
and TR2 should be all right. And if a pulse
noise of approx. 0.2 V /P-P is produced at the
collector of TR3, it also is all right.
NO LED CHANNEL INDICATOR LIGHTS
A) I n the event a specific channel fails to light, it
is probable that there is an open circuit in the
LED display or bad contact in the channel
selector switch.
B) If all channels fail to light, the regulator
(TR36
&
TR37) circuit is defective.
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