| Symptom: |
Frequency jump in LSB
mode after changing modes. |
| Probable
Cause: |
LSB BFO is not being
switched properly by logic; unit may need factory update. |
| Cure: |
With radio turned off,
measure resistance of pin 17 to ground on IC24 chip on main unit.
Should be 47 K. If it measures above one mega-ohm, install a 47 K,
1/8 W resistor over the top of IC24 between pins 10 and 17. |
|
|
| Symptom: |
Radio is off frequency. |
| Probable
Causes: |
Reference oscillator
needs alignment. |
| Cure: |
Field: First reset CPU
to clear all BFO presets, then tune in WWV and align L29 coil on PLL
unit for zero beat in USB mode. Shop: Reset CPU. Align L29 coil for
60.0 MHz at P2 test point. Check alignment of BFO. |
| Remarks: |
Before performing this
alignment, make sure that update to prevent LSB frequency jump has
already been installed in radio (see above cure). |
|
|
| Symptom: |
In IC-736, TX SSB audio
sounds harsh. Average talk power seems low. |
| Probable
Cause: |
Driver and PA idle
current is set too low. |
| Cure: |
Realign idle current as
per procedure on page 5-8 of the service manual with a change in
specs: Adjust R8 for a 300 mA increase and R44 for a 500 mA
increase. Total idle current draw should be about 1000 mA (1 A). |
|
|
| Symptom: |
In IC-736, unit will
not turn on. Unit powers up if VCC cable is disconnected from PA. |
| Probable
Cause: |
Shorted driver and PA
FETs. |
| Cure: |
Replace driver and PA
FETs. Inspect PA unit for overheated components and replace as
necessary. Re-align idle current after repairs as per new specs (see
above). |
|
|
| Symptom: |
Automatic antenna tuner
cannot find tune on some bands, typically 40 and/or 80 meters. |
| Probable
Cause: |
Burned capacitors on
tuner unit. |
| Cure: |
Replace capacitors C2
& C6 (82pf & 100pf) on tuner unit with 500 volt (or higher)
versions. Look for other burned capacitors in same area and replace
as needed. |
|
|
| Symptom: |
Automatic antenna tuner
hunts but cannot find tune on any band. |
| Probable
Cause: |
Bad detector diodes on
tuner CTRL unit. |
| Cure: |
Check these diodes on
tuner CTRL unit: D1, D2, D3, D4, D5, D6, D11, and D12. Replace as
needed. |
| Remarks: |
While tuner is
disassembled, we recommend replacement of C2 & C6 capacitors on
the tuner unit with 500-volt equivalents to prevent future failure
(see above). |
