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| Troubleshooting Guides: IC-737
and IC-737A |
IC-737 only
| Symptom: |
Frequency unstable. |
| Probable
Cause: |
Unstable trimmer
capacitor in BFO. |
| Cure: |
Replace bad plastic
trimmer capacitor C294 (30 pF) 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 capacitor C205 (20 pF) on PLL unit with ceramic equivalent. |
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|
| 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 with ceramic
equivalents. |
| Remarks: |
While the PLL unit is
lifted, it would be a good idea to replace trimmer capacitor C205
(20 pF) 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 relay
(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. |
|
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| 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. If
diodes are good, replace IC10 chip (uPD7533C) on tuner CTRL unit. |
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