Most Common Service Questions for the Icom IC-737 & IC-737A


The information on this page is subject to the terms and conditions set forth on the ICOM America Service FAQ Index page.




IC-737 only


Symptom: Frequency unstable.
Probable Cause: Unstable trimmer capacitor in BFO.
Cure: Replace bad plastic trimmer cap C294 (30pf) on main unit with ceramic equivalent.

Symptom: No RX, no TX. Dead spots in tuning range. Caused by PLL unlock.
Probable Causes: Unstable trimmer capacitor is causing PLL unlock in DDS VCO.
Cure: Replace bad plastic trimmer cap C205 (20pf) on PLL unit with ceramic equivalent.

Symptom: No RX/TX, or distorted audio on one or more bands.
Probable Cause: Unstable trimmer capacitor is causing PLL unlock in HPL VCO.
Cure: Replace four plastic trimmer capacitors, C35, C46, C59 and C70 on PLL unit ceramic equivalents.
Remarks: While the PLL unit is lifted, it would be a good idea to replace trimmer C205 (20pf) in the DDS loop.

IC-737 & IC-737A



Symptom: RX/TX audio pitch change between USB and LSB, i.e. LSB has too many highs while USB has too many lows. RX audio may be "balanced" with the PBT control.
Probable Cause: BFO or PBT oscillator is out of adjustment, or FL-30 filter is bad.
Cure: Re-align BFO and PBT. If this does not correct the problem, replace the filter.

Symptom: Unit will not switch between Antenna 1 and 2. Front panel switch and LED seem to work properly.
Probable Cause: Stuck relay on ANT-SW unit.
Cure: Replace bad RL1 (AE5343) on ANT-SW unit.
Remarks: There is a factory update to prevent this failure in older IC-737s. Call Icom Technical Support for details.

Symptom: Automatic antenna tuner hunts but will not tune on any bands, or sometimes finds a tune on some bands.
Probable Causes: 1) Bad detector diodes on tuner unit. 2) Bad tuner CPU.
Cure: Check and replace faulty detector diodes D6, D7, D8, and D9 on tuner CTRL unit. Diodes are good, replace IC10 (uPD7533C) on tuner CTRL unit.

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