[ICOM] IC-735 misbehaves above 21.9 Mhz

[Gary Fiber]

Yes we used ceramic dielectric caps for replacements. I am not sure if we
ever figured out exactly what the problem was as Icom also poured in some
molten wax to calm microphonic troubles during manufacture of the VCO.

Gary K8IZ.

-----Original Message-----
From: Icom [mailto:icom-bounces at mailman.qth.net] On Behalf Of D C _Mac_
Macdonald
Sent: Thursday, October 29, 2015 6:06 PM
To: Icom Forum
Subject: Re: [ICOM] IC-735 misbehaves above 21.9 Mhz

If I recall correctly, these trimmer capacitors had polystyrene dielectrics.
As they aged, they "outgassed" the plasticizer (like your auto dashboard)
and this film then made the capacitors intermittent at first and then
totally inoperative.  At one time, Icom procured some ceramic dielectric
replacements that were far more stable.  I'm reasonably sure that Scott
Malcolm and other Icom repair facilities can still fix that problem once and
for all.  I'm also certain that Gary Fiber, K8IZ can confirm, expound, or
refute my above statements. 
 
I still have the IC-735 that I bought new sometime prior to 1993! 
 
* * * * * * * * * * *
* 73 - Mac, K2GKK/5 *
* (Since 30 Nov 53) *
* k2gkk hotmail com *
* Oklahoma City, OK *
* USAF & FAA (Ret.) *
* Icom User -- 1972 *
* * * * * * * * * * * 
 
 
> From: gfiber at comcast.net
> Date: Thu, 29 Oct 2015 15:45:34 -0700
> To: icom at mailman.qth.net
> Subject: Re: [ICOM] IC-735 misbehaves above 21.9 Mhz
> 
> There are 4 screwdriver or tuning tool adjustable variable capacitors in
the 735 VCO system. Each one controls a range of frequencies. They are set
so a test point shows a DC voltage, possibly 3 volts on a certain frequency,
that voltage will vary as the radio is tuned through the frequency range the
particular VCO covers. If that voltage is not present the radio will not
operate in a range of frequencies that VCO is designed to control. Hope this
helps.
> 
> Gary P. Fiber K8IZ
> 
> 
> 
> > On Oct 29, 2015, at 2:54 PM, Nathan Moreschi via Icom
<icom at mailman.qth.net> wrote:
> > 
> > Trimmer caps?
> > 
> > Sent from Yahoo Mail on Android
> > 
> > From:"keith.miller5 at comcast.net" <keith.miller5 at comcast.net> 
> > Date:Thu, Oct 29, 2015 at 5:11 PM Subject:[ICOM] IC-735 misbehaves 
> > above 21.9 Mhz
> > 
> > 
> > Hi,
> >   
> > I have an IC-735. 
> > When I turn on the power to the rig, nothing is heard if the last
frequency I was listening to was 22 Mhz or greater. 
> > As soon as I tune down to 21.999 or below, normal signals are heard and
then I can hear normally anywhere on the bands until I turn off the rig. 
> > I can hear an audible relay click when tuning from 21.999 over to
22.000. 
> >   
> > Any suggestions? 
> >   
> > Keith
> > KB0EMP
> > ----
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> ----
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> http://www.qsl.net/icom/ To support QSL/QTH.net: 
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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/ To
support QSL/QTH.net: http://www.qsl.net/donate.html