[R-390] R-390A trouble

Wed, 27 Mar 2002 19:57:46 -0500

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
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
> >
>
>
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