[ICOM] IC-746 tx power problem

Fri Jun 30 15:42:21 EDT 2006

And just to add some more info the the 746 tx issue:

    I just purchased a used 746 pro. I received it this morning via ups and 
it does work fine. It is a late late serial number of 02039?? so it should 
be of recent manufacture. It was sold new in December of 2005 so radio is 7 
months old.

    Inside the box, I found the original purchase receipt. I also found 
paperwork where the owner had to send back for the infamous no tx problem. 
This failed in January of 2006 so the rig dies after approx one month. It 
also included the paperwork from Icom America where the repairs were done.

    So obviously some of the new rigs are dying too, albeit at a slower 
rate. I feel I got a real good price on the rig and love the way the pro 
operates. I guess I am better off for having one that has been repaired 
versus wondering when and if it would die. I guess repeat deaths are kinda 
rare but not unheard of.

    Anyway, it seems to be a good rig, works well now and hopefully will 
continue to do so.

>From: "Bert Almemo" <balmemo at sympatico.ca>
>Reply-To: ICOM Reflector <icom at mailman.qth.net>
>To: "'ICOM Reflector'" <icom at mailman.qth.net>
>Subject: RE: [ICOM] IC-746 tx power problem
>Date: Thu, 29 Jun 2006 23:30:27 -0400
>
>Hi Frank,
>
>Thanks for reply and links. Very interesting reading. Thanks to you and
>everyone else who helped out in this matter. I'll forward all info to my
>friend and I'll let you know how it hopefully was fixed.
>
>73 Bert, VE3OBU
>
>
>
>-----Original Message-----
>From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net] On
>Behalf Of Frank A. Ellis
>Sent: Thursday, June 29, 2006 7:40 PM
>To: ICOM Reflector
>Subject: RE: [ICOM] IC-746 tx power problem
>
>Hi All,
>
>The following may be interesting reading:
>
>http://www.rudius.net/oz2m/ic746pro/index.htm
>
>http://www.qsl.net/k5lxp/projects/746Pro/746ProNoTX.html
>
>
>73, Frank W3UHF
>
>
>
>
>--- Bert Almemo <balmemo at sympatico.ca> wrote:
>
> > 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
> > >
> > ----
> > 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/
> >
> > ----
> > 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/
> >
>
>
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>----
>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/
>
>----
>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/

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