Intermittent Rx Sensitivity. Problem Seems Mechanical.; Noise In Rx, Birdies.; Rx Disappears When Outer Shield Of Antenna Coax Is Connected.; No Tx Output In All Modes. - Icom IC-761 Common Questions

Replace all of these components on the RF unit: D42, D44, D45,
Cure:
D46, D47, Q15. Check C174 and C179 for leakiness. There may be
other failures. Unit is not repaired until listed voltages at C47 are
corrected.
Distorted RX on strong signals. BC band RX sensitivity may low or
Symptom:
marginal.
Probable
Q15 on the RF unit has become leaky.
Cause:
Replace faulty Q15 (2SC2878B). If Q15 is leaky, there may be other
Cure:
problems on the RF unit. See cure for RX problem listed above.
Intermittent RX sensitivity. Problem seems mechanical. Banging on
Symptom:
case or switching between RX & TX may temporarily restore
sensitivity.
Probable
Intermittent contacts in relay on tuner relay unit.
Cause:
Replace RL13 (LY2-0-DC12V) on tuner relay unit.
Cure:

Noise in RX, birdies.

Symptom:
Probable
Voltage regulators on PLL unit are oscillating.
Cause:
Replace overheated C128, C129, C132 and C137 regulator filter
Cure:
capacitors on PLL unit.

RX disappears when outer shield of antenna coax is connected.

Symptom:
Inspection reveals 6 volts DC at the center conductor of the antenna
jack.
Probable
Shorted DC-blocking capacitor C40 on the ANT AW unit.
Causes:
Replace the capacitor.
Cure:
There are probably other problems on the RF unit if this capacitor is
Remarks:
bad. Check the voltages at D47 on the RF unit. Radio may have been
stuck by lightning or sustained a large RF overload through the
antenna jack.
No TX output in all modes. Problem is traced to no output at J8 on
Symptom:
the RF unit.
Probable
Bad Q14 amplifier on RF unit.
Cause:
Replace Q14 (2SC2053). There may be other problems on the RF
Cure:
unit. Check the DC voltages at D47.
The power to the radio flutters on and off when the TX power output
Symptom: