[R-390] Popping noise problem

[Walter Wilson]

That was indeed my problem on one R-390A.  I replaced the coax between the
Diode Load and the Limiter pot/switch, and the problem disappeared.  To
confirm this before you break into the wiring harness, you'll have to
disconnect the existing coax at BOTH ends, and patch in a substitute piece
of coax.

Walter Wilson - KK4DF
http://www.knology.net/~wewilson
(REAL Radios: R-390A(x5), R-390(x2), Viking II, Ranger, Thunderbolt, KWM-2A)

----- Original Message -----
From: "James Miller" <JamesMiller20@worldnet.att.net>
To: "Claudio Spiritelli" <oldradio@tin.it>
Cc: "R-390" <r-390@mailman.qth.net>
Sent: Sunday, January 27, 2002 9:46 AM
Subject: Re: [R-390] Popping noise problem


> I had the same problem with my 390a.  Someone on the list suggested that
> the miniature coax cables were experiencing a breakdown of the center
> insulation due to aging.  After some experimentation, I discovered that
> was indeed the problem.  After replacing the coax cables from the IF
> module to the diode load connector, and from there to the Limiter
> control, my problem was fixed.  Apparently the little coax cables begin
> to break down with age.  Unfortunately this can be a tedious job!  Jim
> N4BE
>
> Claudio Spiritelli wrote:
> >
> > Hello to all,
> >
> > I just discover a problem with my 390A. In order to ear the problem I
must
> > do the following:
> >
> > RF gain .......... completely CCW
> > Local AF gain......completely CW
> > Limiter ...........OFF
> >
> > In this situation there is a "creaking" and "popping" random noise in
the
> > speaker.
> > During normal operation is very hard to ear and only in presence of weak
> > signal.
> >
> > I tried to localize the source of the noise by "sectioning" the
receiver.
> > The AF section does not produce the noise, as well as the RF section.
> > The source appears to be on IF section. I did section more deeply and I
> > removed the "Diode Load" jumper and the noise is still there.
> > This make me to believe that the source is between the "Diode Load
jumper"
> > and the first AF amplifier, witch leaves only the "Limiter".
> > Analyzing the noise with a "scope", I see the noise as a very short but
high
> > spike on the "signal line" in the "limiter" section ( actually when the
> > Diode load jumper is in place, the noise propagate backward to the
detector
> > as well).
> > On the B+ line , I see low frequency variation ( with the scope at is
> > maximum sensibility of 1mV/div) witch I think is the "filtering" trying
to
> > bypass the spikes, so I am assuming that the noise is not coming from
there.
> >
> > When I turn the limiter on, the noise disappear on the audio as well as
I do
> > not see it with the scope and the B+ line does not have any low
frequency
> > variation. That made me to believe that the capacitor C536 was the
cause.
> > Wrong.
> >
> > There are not to many other components in that section that can cause
such a
> > noise and after I replaced the tube ( 5814A), I did run out of options.
> > One more piece of information, it appears that the noise goes away after
the
> > receiver is on for more the 1 hour.
> >
> > Unless my analysis is wrong and the noise has different source, I need
some
> > help from the experts.
> >
> > Thanks for all
> >
> > Claudio Spiritelli
> >
> > _______________________________________________
> > R-390 mailing list
> > R-390@mailman.qth.net
> > http://mailman.qth.net/mailman/listinfo/r-390
> _______________________________________________
> R-390 mailing list
> R-390@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/r-390
>