[R-390] R-390A trouble
David Wise
[email protected]
Thu, 28 Mar 2002 09:13:39 -0800
I agree. I suggested the IF deck only because it's
so easy. It's still possible that IF (fundamental or
harmonic) is getting out of the deck and back around to
the RF, with enough sneaking through to regenerate.
Does the motorboat change with IF bandwidth? If not,
you've eliminated that possibility, one down, ??? to go.
This one's going to be a booger. You'll feel *so*
good when you nail it.
73,
Dave Wise
> -----Original Message-----
> From: Jim Temple [mailto:[email protected]]
> Sent: Wednesday, March 27, 2002 4:58 PM
> To: [email protected]
> Subject: Re: [R-390] R-390A trouble
>
>
> I just checked the tubes on a Hickok 6000A and they test fine, I also
> swapped in a different set. No change. I tapped the tubes
> when the putt,
> putt sound is occuring, and when the antenna trim is detuned
> and there is no
> putt, putt.
>
> I checked the power supply voltages, and I get 260V at F102
> and 225V at
> F103. The 150V regulated is 150.4V.
>
> The sound goes away when V202 1st mixer, V203 2nd mixer, and
> V204 3rd mixer
> are individually removed. I would expect this. Concerning
> V202 1st mixer,
> the sound returns at 8mhz and above, again as expected.
> Also, when V201 RF
> Amp is removed, the sound goes away.
>
> All I can surmise is that one or more of the ceramic caps are
> bad. I can
> shotgun the caps, but it would be helpful if I started with
> the most logical
> stage. I would pick the V201/6DC6 and go from there. What
> do you think?
>
> Jim
>
> ----- Original Message -----
> From: "Barry Hauser" <[email protected]>
> To: "David Wise" <[email protected]>; <[email protected]>
> Sent: Wednesday, March 27, 2002 7:26 PM
> Subject: Re: [R-390] R-390A trouble
>
>
> > The "Yeah, But Dept." chimes in:
> >
> > Yeah, but ... the screeching/motorboating kicks in above
> the 3 MC band
> only.
> > Doesn't that suggest the RF deck?
> >
> > The Dumb Suggestions Department:
> >
> > Jim - did you test the tubes? Do the tap test on them?
> Even so, some
> tube
> > in the RF deck might not be handling higher freqs. (or a
> cap or something
> > else). That means swapping out some -- or swapping around.
> I'd also
> loosen
> > and retighten likely screws/ground connections. Sometimes
> the oxidation
> or
> > residue of MFP varnish can create an unplanned capacitor to
> ground rather
> > than ground connection, or maybe even a diode -- or maybe
> even an LSI
> audio
> > chip with onboard RF chip with programmable screech and motorboat
> sounds. --
> > OK, maybe not that. ;-)
> >
> > Barry
> >
> >
> > ----- Original Message -----
> > From: "David Wise" <[email protected]>
> > To: <[email protected]>
> > Sent: Wednesday, March 27, 2002 6:30 PM
> > Subject: RE: [R-390] R-390A trouble
> >
> >
> > > Sounds to me like regeneration, frequently
> > > caused by a bypass cap letting go or something
> > > losing its ground. That bad ground you fixed
> > > might not be the only one.
> > >
> > > Divide and conquer. Got another IF deck?
> > > Swap it in; that's where most of the gain is.
> > >
> > > What do you gentlemen think?
> > >
> > > 73,
> > > Dave Wise
> > >
> > > > -----Original Message-----
> > > > From: Jim Temple [mailto:[email protected]]
> > > >
> > > > OK, I want to fix this receiver. Here goes.
> > > >
> > > > 1. R-390A bought as a "massacre" yellow line from Fair Radio.
> > > > 2. After cleaning, and replacing many of the "problem" caps
> > > > (listed on many
> > > > of the resident web sites), I corrected a below 8mhz problem,
> > > > by finding
> > > > that the ground lug under T-207 was loose and insulated from
> > > > ground by a
> > > > shellac layer.
> > > > 3. The unit, at first alignment, aligned well.
> > > > 4. At some point, within a couple of hours of
> operation, the receiver
> > > > developed a screeching/motorboat putt putt sound.
> > > _______________________________________________
> > > R-390 mailing list
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> > > http://mailman.qth.net/mailman/listinfo/r-390
> > >
> >
> >
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>
>
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