Troubleshooting Hints; Unit Will Not Turn On; No Receive Sound; No Noise - Realistic TRC-449 Service Manual

5. TROUBLESHOOTING HINTS
UNIT WILL NOT TURN ON
1. Broken DC Power cable.
2. Fuse blown. Be sure you check the cause.
3. Defective power switch.
4. Defective wires or poor soldering in power
supply circuit.
NO RECEIVE SOUND
1. Defective R F circu it in receiver.
2. Defective Noise Blanker.
3. Defective AGC circuit.
4. Defective PLL circuit.
5. Defective antenna connector.
NO NOISE
1. Defective RX power circuit.
2. Defective RX audio circuit.
3. Defective PLL circuit and/or channel switch.
4. Defective squelch.
5. Defective PA-CB switch and/or EXT SP. Jack.
FOR MORE HINTS, SEE BELOW:
NO RECEIVE SOUND
A) Check for short circuit or broken wire in the
winding of the output transformer{T-1) or
cold soldering between the wires and printed
circuit board. The DC resistance of the output
transformer winding is approximately 0.2
ohm on the primary side and 0.5 ohm on the
secondary side (use accurate V.O.M. if availa-
ble to check this resistance).
B) Defective Audio Power IC4.
Check the DC voltage at pin 10 of IC4. If
voltage reads approximately 7 V (supply
voltage/2), then problem is not with th is I C.
C) Squelch is ON all the time.
I f the gate voltage of F ET3 is +6 V or less
with Squelch Control in the C.C.W. position,
the Squelch Circuit is defective. So, check the
circuits of TR12, TR13 and TR14 and also
ground terminal of Squelch Control (VR404)
for cold soldering.
If the collector voltage of TR 12 is 6 V or
more, check the circuit of TR21 and Volume
Control (VR405).
D) If the Signal strength meter deflects when the
external antenna is connected, you can as-
sume that RF thru I F stages are OK. So,
checks shou Id be made on detector and AN L
circuit (D10, D11 and D12).
NO TRANSMISSION
1. Broken or bad contact in microphone con-
nector .and/or push-to-talk switch.
2. Broken or bad contact in antenna connector.
3. Defective Relay.
4. Defect in power supply.
5. Defect in PLL and/or Carrier Oscillator (Im-
proper adjustment).
6. I noperative microphone amplifier and/or bal-
anced modulator in SSB mode.
7. Defective TX AMP.
(Between mixer and final stage)
NO MODULATION
1. Defective microphone.
2. Defective microphone connector.
3. Defective TR20 or IC4, (AM mode.)
4. I noperative microphone amplifier, (both AM
and SSB modes.)
If a negative voltage appears at the cathode
of D 12, detector and AN L circuit should be
all right, so, check the circuit of TR 15.
If the collector voltage of TR 15 is approx. 6
to 7 V, TR 15 is all right.
E) No receive sound even with carrier oscillation
(7.B MHz) on USB/LSB mode.
I n case of no signal strength meter deflection
at the check of D) above: If a RF voltage of
2V /P-P(34 MHz) or more is at the first gate
of FET1 and this frequency is as shown in
the frequency chart, the local oscillator (PLL)
shou Id be all right.
F) Check the voltage of each part of the follow-
ing stages: TR9, TRB, TR6, FET1, TR5 and
TR4 (in this order).
NO TRANSMISSION (AM)
A) Connect the DC meter in series with DC
power cable. If reading is 1.5 A or more, you
can assume that there is contact failure be-
tween relay and antenna circuit or short
circuit between final transistor (TR43) and
antenna circuit.
I f the cu rrent reads 1.5 A or less, check prior
stages.
B) If the output voltage (7.B MHz) of carrier
oscillation (TR27, TR2B) is 100 mV or more
at TP-9, the carrier oscillation circuit is . all
right.
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