[R-390] R-390A trouble

Wed, 27 Mar 2002 19:26:55 -0500

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
>