Icom IC-740 Common Questions page 2

Although resoldering the connector pins is a delicate and time
Remarks:
consuming procedure, it will save you a great deal of troubleshooting
time and frustration.
TX power output is marginal on some bands. (Compressor switch has
Symptom:
already been replaced.) ALC meter reading is low and steady, not
erratic. Adjusting ALC pot does not increase power. Troubleshooting
reveals that no specific stage is malfunctioning.
Probable
TX IF needs to be aligned.
Cause:
Set unit to 14.100, TX in RTTY mode, and adjust L8, L10, and L11
Cure:
on IF unit for peak ALC meter reading.
If the above steps have no effect, troubleshoot for a defective TX
Remarks:
stage, or follow steps for curing erratic TX.
Power gradually drops off when warm. ALC meter indication
Symptom:
remains at mid-scale. Adjusting ALC does not help.
Probable
APC misalignment.
Cause:
Realign ALC, Ic METER, and APC as per pages 9-1 and 9-1 in the
Cure:
service manual.
VFO tuning is erratic, sometimes skips when changing frequencies or
Symptom:
bands. Displayed frequency sometimes does not increment smoothly
when VFO knob is turned slowly.
Probable
Dirty rotary encoder.
Cause:
Remove white plastic cover from back of rotary encoder and spray
Cure:
clean the carbon track with Blue Showers solvent. Spin VFO knob
vigorously while spraying.
When cleaning the rotary encoder, do not let solvent saturate the
Remarks:
display unit or allow it to come into contact with the plastic display
lens. Stuff a paper towel between the rotary encoder and display unit
to catch spray run-off.
Unit jumps frequency unexpectedly when turning VFO knob. Digital
Symptom:
display does not track with this jump. The frequency jump is
consistent and happens in the same place every time. Actual
operating frequency and displayed frequency do not match in some
parts of the bands.
Probable
PLL is out of alignment.
Cause:
Be sure you don't have a rotary encoder problem, first. Try realigning
Cure:
the LDO as per the second "9-1" page in teh service manual. If this
doesn't help, follow the complete alignment procedures for the PLL
on both "9-1" pages in the service manual with the exception of the
PLL Lock adjustment.