[ICOM] ic 746pro

[Dan Cotsirilos K9DTC]

Has anyone every had any experience with a 746pro that had dead receiver 
below 2 meters? Their is audio and the internal calibrator shows signal but 
it seems like the ant is not reaching the front end?


Dan K9DTC



----- Original Message ----- 
From: "Bert Almemo" <balmemo at sympatico.ca>
To: "'ICOM Reflector'" <icom at mailman.qth.net>
Sent: Thursday, June 29, 2006 2:04 PM
Subject: RE: [ICOM] IC-746 tx power problem


> Hi Paul,
>
> Thanks for your reply and suggestions. I don't know the difference in the
> circuitry between the 746 and 756pro2 and if the problem you're describing
> relates to the 746.
>
> I know that the 746 had a lot of problem with the IC151 in the beginning.
> ICOM modified the circuitry in the later ser.nos to fix the problem. What
> I'm really after is what ICOM did to fix the problem permanently. I've
> surfed the ICOM site but can't find anything relating to this problem. If
> anybody can shed some light on this I would really appreciate it.
>
> I'll check the mods.dk fix regarding the relay as I haven't seen or heard 
> of
> that one before. When my friend's 746 is fixed I'll post what was done to
> bring it back to normal again.
>
> 73 Bert, VE3OBU
>
>
>
>
> -----Original Message-----
> From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] 
> On
> Behalf Of Paul Playford
> Sent: Thursday, June 29, 2006 12:59 PM
> To: ICOM Reflector
> Subject: Re: [ICOM] IC-746 tx power problem
>
> When IC151 failed in my IC-756PROII, I also found a shorted PIN diode and 
> .1
> Uf coupling capacitor in the adjacent circuitry shorted.  I concluded the 
> .1
> Uf capacitor went first and took everything else with it.
>
> Then later a problem with my radio surfaced on 10m.  It would go to full
> output as soon as the transmitter was keyed, regardless of the RF POWER
> setting.
>
> My fix was to just stay off of 10m as the sun spots were going away.
>
> Then I acquired a 6m antenna and I was back to full output.
>
> So the radio went on the bench.
>
> All was well (into a dummy load).
>
> Back in service, no worky.
>
> I found that by paralleling the dummy load and the antenna on 6m the radio
> worked fine.  Cost me 3dB on receive but the preamp overcame that.
>
> Then the mods.dk fix was suggested to me.  I installed the relay and now 
> all
> is well on all bands.  Three years and no further problems.
>
> As the modification suggests: there is just too much coupling between the 
> NO
> and NC reed relay pins and during transmit (and perhaps with a little swr)
> enough rf feeds back into the input of IC151 to cause the oscillation.  I 
> am
> convinced that that oscillation shorted the capacitor and PIN diode and
> killed IC151 the first time around.
>
> de Paul, W8AEF
>
> ----- Original Message -----
> From: "Bert Almemo" <balmemo at sympatico.ca>
> To: "'ICOM Reflector'" <icom at mailman.qth.net>
> Sent: Thursday, June 29, 2006 6:20 AM
> Subject: RE: [ICOM] IC-746 tx power problem
>
>
>> Hi Paul,
>>
>> Thanks for your reply. I have been to mods.dk and I found a couple of
>> articles about the tx problem. I'm just wondering if there is more to it
>> or
>> if this is all you have to do to get rid of the problem?
>>
>> The only answer I got was from you so I hope someone else is reading this
>> and might have some more comments. Thanks.
>>
>> 73 Bert, VE3OBU
>>
> ----
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> Icom Users Net: Sundays, 1700Z, 14.316 MHz
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>
> ----
> Your Moderator: Dick Flanagan K7VC, icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
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