Icom IC-740 Common Questions

Most Common Service Questions for the Icom IC-740
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Service FAQ Index page.
Distorted RX/TX, or no RX/TX on one or more bands. Distorted SSB
audio sounds raspy and rough. Problem may be temperature related.
1) Bad trimmer capacitors on PLL unit, HPL VCO section.
Replace plastic trimmer capacitors C4, C15, C24, and C33 with
ceramic equivalents.
Any of the following: 1) No RX/TX at all. Display normal. 2) No
CW operatoin. 3) Some front panel controls do not operate reliably.
Burned or open on R1 on reg. unit.
Replace R1 (4.7 ohm, 1/2 watt).
Intermittent no/low TX output. Jiggling or pressing the compressor
switch causes the power to return to normal.
Bad compressor switch. (This is a common failure in the IC-740)
Replace (do not clean) the compressor switch.
Low, erratic TX output in all modes. (Compressor switch has already
been replaced.) ALC meter reading is unsteady and may drop out
altogether. Removing the top cover may cause problem to disappear
for a while. Pressing on the wiring harness near the IF unit may cause
the power/ALC meter reading to fluctuate. Problem may be
temperatuer related.
1) Poor solder joints on IF unit. 2) Dirty RF power/mic gain pot. 3)
Poor connections at IF unit is causing low TX drive. This is
sometimes caused by oxidation at the point where the wires is
crimped to the connector pins. 4) Bad relay on FM unit (if installed).
Clean dirty RF power/mic gain pot. Resolder cracked and suspicious-
looking joints on IF unit. If these do not help, remove and resolder
the wire crimps in the RF connector pins in J2, J5, J12, J9, J19 and
J20 on the IF unit. Be sure to not add too much solder to the
connector pins or they will need to be replaced. Be sure all
connectors are fully seated after repair. Replace RL1 on the FM unit.
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