[Icom] IC746PRO

Sat, 9 Mar 2002 06:36:01 -0000

Yup, same transistor failed in my '765.  Several times, along with filter
switching diodes.  Turned out to be a less than adequate connection between
my station ground and my tower.  Everytime I turned my antenna the Ham M
rotator applied 2 to 3 volts a.c. to the housing of the rotator (via the
direction indicator potentiometer wiper) at the top of the tower which fed
back down the feed line and blew the transistor.  If you look really close
at the IC-765 schematic you will find a sneak path for this voltage to get
to the base of the pre-driver transistor.  I stumbled on to the cause of
this by installing a couple of diodes in parallel across the antenna
terminals (I was getting desperate after so many failures) to see if
atmospheric static was destroying the transistor.  The next time I turned
the antenna I heard the most god-awful buzz from the radio.  To prove the
cause I just put a ground lifter on the rotator control and the buzz went
away.  I now have a good connection between my tower and station ground and
no further problems.

Can't help but wonder how many of these pre-driver transistors have given
the '765 a bad reputation when the problem is caused by external faults.

de Paul, W8AEF

----- Original Message -----
From: Tony Hwang <[email protected]>
To: <[email protected]>
Sent: Sunday, March 10, 2002 3:16 AM
Subject: Re: [Icom] IC746PRO

> Hi,
> I dare to say some of questions asked from high end radio owners make me
> wonder. Maybe something to do with operators? No matter how well
> equipment is made, if the operator does not know how to operate it
> properly, then it can easily break. My old 765 had exactly same problem
> the same x-sistor you mentioned went once and repelacing it was a cinch.
> Just took time to warm up the soldering iron. I think QC standard of
> operators in general as well is questionable these days. Looks like
> everybody is becoming an AO.
> 73,
> Tony, VE6CGX
>
> "George, W5YR" wrote:
> >
> > Which raises the question as to why so many postings on the TT list are
> > concerned with user mods and fixes to correct problems that sound like
they
> > should never occur with properly designed equipment manufactured under
even
> > minimally adequate QC standards.
> >
> > Having to resolder joints, reroute and reseat cables, tighten mounting
> > screws, and add shielding, ferrite beads and bypass caps to correct
> > internal RFI problems does not strike me as evidence of QC to be
admired.
> > In contrast, my 11 year old Icom IC-765 has had only one part failure:
the
> > transmitter pre-driver transistor. And my 756PRO which has been operated
up
> > to 18 hours a days for the past year and a half has yet to hiccup or
fail
> > to perform in every respect according to spec. And my 1982 IC-730 has
yet
> > to require any maintenance at all.
> >
> > I must be missing something here . . .
> >
> > 73/72/oo, George W5YR - the Yellow Rose of Texas
> > Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
> > Amateur Radio W5YR, in the 56th year and it just keeps getting better!
> > QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
> > Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437
> >
> > All outgoing email virus-checked by Norton Anti-Virus 2002
> >
> > "Caitlyn M.Martin" wrote:
> > >
> > > On Fri, 8 Mar 2002 23:44:16 -0500
> > > "Steve Jones" <[email protected]> wrote:
> > >
> > > > Thanks for the photos, but unless Ten Tec gets their QC fixed, I
would not
> > > > touch a radio from there. I like my FT1000D too much, Looking at the
Pro II
> > > > now, especially new for 2735.00. 73, Steve
> > >
> > > Hmmm... based on my experience, I'd take Ten Tec QC over Yaesu any
day, and over Icom on most days.
> >
> > ----
> > Your Moderator: Dick Flanagan W6OLD, [email protected]
> > Icom FAQ: http://www.qsl.net/icom/
> ----
> Your Moderator: Dick Flanagan W6OLD, [email protected]
> Icom FAQ: http://www.qsl.net/icom/
>