Icom IC-735 Common Questions page 3

Probable
Bad rotary encoder.
Causes:
Substitute rotary encoder with a known good one. It is recommended
Cure:
that the rotary encoder be replaced as a complete assembly if it is
bad.
If the frequency tunes in only one direction, i.e. either up or down,
Remarks:
there may be a problem on the logic unit.
No display, RX/TX. Inspection reveals PLL unlock.
Symptom:
Probable
1) Low power supply voltage. 2) Bad IC8 on PL unit.
Causes:
Measure power supply voltage at pin 7 of either accessory jack.
Cure:
Should be not less than 12 volts for reliable operation. If OK, replace
IC8 on PL unit.
No RX/TX when cold or warm. May have dead spots in tuning range
Symptom:
of each band.
Probable
PLL unlock
Causes:
Align LPL lock voltage on PL unit.
Cure:
Frequency unstable in TX on 10 meters, especially after warm-up.
Symptom:
Probable
PL unit needs factory update.
Causes:
On PL unit, change value of R163 from 3.3k to 1.5k, and spread coil
Cure:
L36.
Mic gain is low when using Heil microphone element.
Symptom:
Change value of R235 on PL unit to 200k.
Cure:
Radio trips/shuts down power supply when power connector is
Symptom:
plugged in, even when radio is turned off.
Probable
Shorted PA transistors.
Cause:
Replace shorted PA transistors. The pre-driver and driver transistors
Cure:
are probably bad too. Check electrolytic capacitors C25 and C29 on
PA unit for swelling and replace if needed.
Drastic change in audio frequency response between USB and LSB.,
Symptom:
i.e. USB audio has too much bass while LSB audio has too much
treble. USB/LSB RX frequency response may be equalized, to a
degree, by adjustment of the front panel PBT control. TX frequency
response remains poor.
Misadjustment of the BFO and/or PBT shift oscillator, or bad FL-30
Probable
on main unit.
Cause:
Realign the BFO and PBT shift oscillator. If this doesn't help, replace
Cure:
the FL-30.