[ICOM] IC761 problem

[Gary P. Fiber]

I forget what the reference is, think it was 30.72 MHz, maybe twice 
that. So that could explain the 70 MHz you are seeing on your GDO.
Have you looked at the Icom America support knowledge base web page 
under IC-761?
There are twenty faults the techs found over the years that seem to be 
more common.
http://www.icomamerica.com/en/support/kb/Default.aspx

If you have been there then what are the symptoms you are having?
I understand no receive, how about transmit any at all?
Does it switch between Transmit and receive?
Seems to me there was a calibrator signal available do you hear that? 
Switch might be inside the case on main unit.
Is there any DC Voltage on the center socket of the main coax connector?
My guess would be to look on the RF Unit.
The display seems to be working, so does the preamp and speakers and 
possibly IF stages. DP-6 on the display board must be working.
All of these details help troubleshoot or may not until someone can stab 
it with a voltmeter.
But we can try to assist.


      Knowledge Base Article 5BAH223436

Issue
My 761 has no or very low RX sensitivity.

Resolution
Bad components on the RF unit, probable result of RF overload. To verify 
this, check DC voltages at D47 diode on RF unit. Correct voltages are: 
Cathode side- RX: 8.5 V, TX: 13.8 V. Anode side- RX: 9.0 V, TX: 9.5 V.

Replace all of these components on the RF unit: D42, D44, D45, D46, D47 
diodes, Q15 transistor. Check C174 and C179 capacitors for leakiness.

Category
Amateur : HF : 761

Gary K8IZ






On 5/19/2010 3:12 PM, Alan wrote:
> Hi Gary,
> Well I have run my Grid Dip Oscillator across the band(20 metres) which
> it is switched to at the moment and can not pick up a signal from the
> GDO. The noise increases when I hook a wire to the antenna terminal
> which suggests the RF stage is partly working and also turning the
> preamp off and on changes the noise level, and the RF gain control also
> controls the noise and the meter.
> I believe that I am picking up a signal from the gdo around 70Mhz (my
> gdo is homebrew and not calibrated up there)but it is untuneable making
> me think that the ocillator to the first Mixer is not operating, and
> according to the book that is coming from a PLL circuit, so I wanted to
> be sure that the same PLL wasnt also involved with driving the digital
> frequency read out which is functioning correctly
> Alan ZL3KR
>
>
>
>
> On 20/05/2010 00:13, Gary P. Fiber wrote:
>    
>> Alan,
>>
>> What are the problem symptoms? No Transmit or receive at all? Dead spots
>> when you tune through the bands?
>>
>> The display is a readout no oscillator from the display helps operate
>> the PLL for the IC-761.
>>
>> On 5/18/2010 9:47 PM, Alan wrote:
>>
>>      
>>> My IC761 sounds like it is running without frequency control (like a PLL
>>> oscillator is not running)
>>> but the digital read out is working perfectly where it tunes and
>>> switches bands without a problem.
>>> Does the PLL oscillator that produces the 70Mhz signal for the 1st Mixer
>>> also in use for the digital frequency display or are they seperate?? I
>>> am trying to get some idea of where maybe I should start to look for the
>>> problem.
>>> Any advice appreciated
>>> thanks   Alan Z:L3KR
>>>
>>> ----
>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>> Icom FAQ: http://www.qsl.net/icom/
>>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>>>
>>>
>>>
>>>        
>> ----
>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>>
>>
>>      
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> To support QSL/QTH.net: http://www.qsl.net/donate.html
>
>    


-- 
Gary P. Fiber K8IZ
Electronic Communications Systems Technician - Field
Electronic surveillance technician
General Radio Telephone Operators License PG-19-6691,
  with Shipboard Radar Endorsement.
Washington State Resident.