[R-390] (I found the problem) NOT!!

Fri, 29 Mar 2002 14:32:13 -0700

Seems to me I recall something similiar to this , and it had to do with the
wiring of the tube socket being incorrect from day one...I think it might have
been pat of the reason the actual wiring and the manual shows changes in the
wiring to the tube... Or again I could be totally off base as I do not have my
manual with me right now...Perhaps the wiring itself had been changed also to
get every bit of gain from the tube possible... I still think that feeding RF
into the rig past the tube at the test point might help to really localize the
problem... But again I am operating on only 2 hours of sleep last night so this
may actually sound comical..!!! 73 de Jordan

Bill Hawkins wrote:

> What we have here is a case of the RF Amp picking up enough
> energy from somewhere to make it oscillate. All you need is
> a gain greater than one and a 180 degree phase shift.
>
> The fact that taking the IF gain from one end to the other
> causes no change in the symptoms kinda lets out the IF Amp
> module. It is time to concentrate on the RF and Antenna modules.
>
> I'd try putting a 0.01 mfd disk from the RF Amp grid to
> ground. The easiest place to try this is E208 or wrap a wire
> around pin 1. If that stops it, the pickup is in the Antenna
> circuits or the AGC line. Then try grounding pin 2 (cathode).
> If that does it, the trouble is in the MGC line. Last, try
> the bypass cap on pin 6 (screen, B+ level).
>
> Regards,
> Bill Hawkins
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Jim Temple
> Sent: Friday, March 29, 2002 11:51 AM
> To: [email protected]
> Subject: [R-390] (I found the problem) NOT!!
>
> Alas, life is not so simple.
>
> After a smooth replacement of Pin 1 of the 6DC6, (work with the dimple), and
> reconnection of the leads, the symptoms remain.
>
> The symptoms are essentially the same as below, except the putt,
> putt/screeching is more intermittent.  All bands except 3 and below are
> affected.  The putt, putt/screeching is most pronounced with peaking of the
> antenna trim control.
>
> A new observation is that with careful peaking of the putt, putt, I can
> almost stop the putt, putt on a PUTT.  At this point, I hear harmonics.
> Tapping anywhere on the chassis will produce stronger harmonics.  Tapping on
> the 6DC6 will produce very strong harmonics.
>
> I replaced the 6DC6 with two other tested tubes, with no improvement.
>
> I will relist the total list of symptoms in a couple of hours.
>
> For now, I am going to test/shotgun all the components associated with the
> 6DC6.  Any other suggestions??
>
> Hard at work,
>
> Jim
>
> ----- Original Message -----
> From: "Jim Temple" <[email protected]>
> To: <[email protected]>
> Sent: Friday, March 29, 2002 10:52 AM
> Subject: Fw: [R-390] R-390A trouble (I FOUND THE PROBLEM)
>
> > CORRECTION.  The pin number is pin 1 (one).  With all those leads, walls,
> > shields, and components to hack through, I miscounted the pin number.
> >
> > It is PIN 1.
> >
> > Jim
> >
> > ----- Original Message -----
> > From: "Jim Temple" <[email protected]>
> > To: <[email protected]>
> > Sent: Friday, March 29, 2002 10:44 AM
> > Subject: Fw: [R-390] R-390A trouble (I FOUND THE PROBLEM)
> >
> >
> > > After wiggling almost all the leads to confirm security, I discovered
> the
> > > following.....
> > >
> > > Pin 5 of V201/6DC6, from the underside, seemed to be in place and
> secure.
> > > Upon wiggling, it seemed loose, so I gently tugged on the pin lead and
> it
> > > came out of the socket from below the plastic.  It was broken between
> the
> > > socket pin and where it emerges from the socket mold on the bottom.
> > >
> > > Apparently, there was enough contact to do the initial alignment, and
> > after
> > > a couple of hours burn in, it insulated itself, creating the below
> > symptoms.
> > >
> > > What was maddening was that the break was within the plastic mold of pin
> > 5,
> > > which took a tug to break it from the plastic.  Three components are
> > > attached.  Later I will summarize what was affected and the fix.
> > >
> > > WOW......this is one for the books.
> > >
> > > I think I will go for replacement, but if there is an easy fix, I will
> > > consider it.
> > >
> > > Well, thats it.  Thanks for the support and help with this problem.
> After
> > I
> > > complete the repair, I will post a summary of the symptoms and fix.  So
> > long
> > > for now.
> > >
> > > Regards,
> > >
> > > Jim
> > > 73, KF4ICZ
> > >
> > > ----- Original Message -----
> > > From: "Jim Temple" <[email protected]>
> > > To: <[email protected]>
> > > Sent: Thursday, March 28, 2002 10:56 PM
> > > Subject: Re: [R-390] R-390A trouble
> > >
> > >
> > > > OK, I replaced C227 .047.  The old one measured .075 when out of
> > circuit.
> > > I
> > > > have a picked-over RF parts deck that happend to have this cap.  It
> > > measured
> > > > .04745, so hopefully this is the problem.
> > > >
> > > > HOWEVER, I am going to clean, inspect, wiggle, tap, eyeball, and
> > generally
> > > > give it the twice over before reinstalling in the morning.  I'm
> winding
> > > down
> > > > for the night.
> > > >
> > > > Will report back after reinstallation of the RF deck in the morning.
> > > >
> > > > Thanks for the great support and suggestions.  Good night.
> > > >
> > > > Regards,
> > > >
> > > > Jim
> > > > 73, KF4ICZ
> > > >
> > > > ----- Original Message -----
> > > > From: "Barry Hauser" <[email protected]>
> > > > To: <[email protected]>; "Jim Temple" <[email protected]>;
> > > > <[email protected]>
> > > > Sent: Thursday, March 28, 2002 9:55 PM
> > > > Subject: Re: [R-390] R-390A trouble
> > > >
> > > >
> > > > > > Barry, I think you've got it.
> > > > > >
> > > > > > But I thought of another thing to try. Because the set is
> > > > > > oscillating within itself, something common to the IF and
> > > > > > RF decks is carrying energy between them.
> > > > > <snipped>
> > > > >
> > > > > Got what?  I dunno, but, hey, Bill, I think YOU"RE onto something.
> > Jim
> > > > > should check out all those jumpers with the mini-BNC's -- maybe one
> of
> > > 'em
> > > > > was swapped with that Skyhighgain cable Norman told us about.
> > > > >
> > > > > Seriously, tho' -- wasn't that another thing that could cause weird
> > > > > problems -- bad mini-coax?
> > > > >
> > > > > When the rational, logical, informed, incisive, deductive approach
> > fails
> > > > ...
> > > > > Well, let's consider ALL the clues ...
> > > > >
> > > > > Squeal -- loud disturbing noise, alarm, or (sl.) to give
> information,
> > to
> > > > > "rat" on.
> > > > > Happens over 3 MC's, that could be written as >3.  Looks like a
> bird,
> > > > don't
> > > > > it?
> > > > > Motorboating, boats, water, ocean -- could be a seagull, or maybe
> > > > > "putt-putt" = golf
> > > > > Then there's the thing about cats.  Wait a minute!  A bird that
> looks
> > > like
> > > > a
> > > > > rat is a bat -- but then what's golf got to do with it?  This is
> going
> > > > > nowhere -- might mean something to a witch.  Is Les around?
> > > > >
> > > > > Forget all that -- pull the RF deck and check it out.  Could be an
> > > > > "underneath-ARGHHH-do-I-hafta?" problem.  Give it the close eyeball
> > > > > inspection.  By all means CLEAN the bandswitch -- twice. (unless I
> > > missed
> > > > > something and you did that already)
> > > > >
> > > > > Nobody seems to be focused on the >3 thing.  Why would this problem
> > kick
> > > > in
> > > > > there?  What is different circuitry-wise about 0-1-2-3 vs 4+?  I
> guess
> > > one
> > > > > thing might be a rotor section or two on the bandswitch, no?  Maybe
> > not.
> > > > > Any particular reason a bad cap would cause the squeal and
> > motorboating
> > > to
> > > > > start at 4 MC's?
> > > > >
> > > > > Great, now I'm gonna be up all night 'cause of somebody else's
> radio.
> > > > >
> > > > > Barry
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > _______________________________________________
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> > > > >
> > > >
> > >
> >
> >
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