[R-390] R-390 NON A Problem

Sun, 13 Oct 2002 00:47:35 -0700

Hi, Dave

I believe you can remove the coil by first removing the two screws on the
top of the can.  I haven't tried it, but believe all the cans in the RF
section are plug-in, and you can simply lift the can after removing the
mounting screws.

If not, you can make the same test from the plate pin of the 6C4.

No, don't have any extender cables.  You can test quite a bit in the
receiver by making use of tube pins and the test points that are available
from the top of the chassis.

Of course the radio will not operate correctly with either the tube removed
or the transformer out, but if the cap you suspect is bad, it shouldn't
matter.  I am assuming you will be looking at the circuitry with a scope or
at least an analog voltmeter.

I don't think there is any problem removing V205.  A number of other tubes
are in series, but they will simply not light.  They won't have an impact in
observing leakage or intermittent noise in C325.  If it is bad, it will
merrily raise hell all by its lonesome.  Of course if it is really
intermittent, it will probably notice you are trying to find it and work
perfectly while you are testing.

73 de Bill, AB6MT
[email protected]

----- Original Message -----
From: "Dave Faria" <[email protected]>
To: <[email protected]>
Sent: Saturday, October 12, 2002 4:03 PM
Subject: Re: [R-390] R-390 NON A Problem

> Thanks for responding bill.  The problem is on all bands.  A dumb question
> but, how do u temporarily remove T207 - what do u mean?  I think to do
what
> u r suggesting would require extender cables to operate on the RF deck
> outside the main chasis - right?  I don't have those.
>
>
> Thanks Dave
>
>
> >From: "Bill Smith" <[email protected]>
> >To: "David Faria" <[email protected]>,<[email protected]>
> >Subject: Re: [R-390] R-390 NON A Problem
> >Date: Sat, 12 Oct 2002 15:29:15 -0700
> >
> >Temporarily remove T207 and watch pin 5 of that transformer.  Also watch
> >the
> >B+.  If pin 5 fluxuates with the static, or if there is any voltage drop
> >between B+ and that pin (across R220), then you have verified a defective
> >C325.  If the B+ and pin 5 fluxuate together, then you need to look
> >elsewhere.  In fact, C325 should smooth any fluxuation if the problem is
> >elsewhere.
> >
> >Depending on the quality of the caps in the RF deck, you may only need to
> >replace the one capacitor.
> >
> >Are you having problems on all bands?  I have had to replace mica caps,
> >even
> >very small values, in the R-390 grid circuits in mine.  They were leaky
and
> >readily detected using a Simpson 260.
> >
> >73 de Bill, AB6MT, NNN0BIO
> >[email protected]
> >
> >----- Original Message -----
> >From: "David Faria" <[email protected]>
> >To: "r-390" <[email protected]>
> >Sent: Saturday, October 12, 2002 5:13 PM
> >Subject: [R-390] R-390 NON A Problem
> >
> >
> > > GE List.  I'm playing with one of the nicest 390's I've seen in a long
> >time
> > > and its got a rather irritating problem.  It has what I would call a
> >static
> > > crash ever so often and I was curious if anyone else has had this
> >problem.
> > > I think its a leaky cap. on the RF Deck.  I have by-passed the tube
> >stages
> > > one at a time on the deck using a tube extender with a filament
resistor
> >to
> > > to maintain the remaining tubes on the deck.  The filaments r in
series.
> >I
> > > seem to have narrowed it down to the last mixer in the series(V205)
> >using
> >a
> > > scope and bypassing.  I am seeing fluxuations in both the grid and
plate
> > > voltage when the crash occurs(Pins 1 and 6).  My guess is c-325 off
the
> > > plate circuit of that tube.  Any speculation would be appreciated.  Is
> >it
> > > typically the plate cap. leaking to ground that would do this?  Would
a
> > > capacitor checker be able to determine if this cap is bad?  What is
the
> > > reason the cap will just not fail?
> > >
> > > I've checked all the tubes on a TV2 and thumped em trying to create
the
> > > problem.  I have replaced all the modules except the RF deck and the
> >problem
> > > is still there.  Sometimes it will run for 30 minutes without a
problem
> >and
> > > then start.  This is a very nice unit and I don't want to recap.
unless
> >its
> > > necessary.
> > >
> > > Thanks for ur responses
> > > Dave Faria
> > > _______________________________________________
> > > R-390 mailing list
> > > [email protected]
> > > http://mailman.qth.net/mailman/listinfo/r-390
>
>
>
>
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