[R-390] Lightning crashes in audio

[Larry H]

Hi Stan,  I think you are right about it probably being a cap going bad.
However, it could also be a tube, the band switch, or resistor. You can try
tapping on the side of the tubes.  The bad cap is probably in the RF deck,
though.  You can narrow it down a little by pulling the tubes in the signal
path 1 by 1 and see where it stops or starts.  I'd start at the RF amp and
work forward.  Also, it could be related to a particular band, and perhaps
above 8 MH or not.  If it's related to a band, you can try pulling the
tuning cans and see if it's related there.  Have fun.

Regards, Larry

On Sat, Aug 15, 2020 at 7:13 PM Stan Gammons <sg063015 at gmail.com> wrote:

> Hi All,
>
> I have an R-390A that I recently put back on the bench and noticed it
> has developed a lightning crash sound in the audio. It's much more
> noticeable with no signal.   It appears the problem is around the 1st IF
> amp.  With a scope on the plate of the 1st IF amp I can see the signal
> change when I hear the lightning crash sound.  Some time ago I replaced
> all of the black beauty caps with orange drops. The cap that goes bad
> and takes out the mechanical filters has been replaced too.  I didn't
> replace the disc, which I assume are ceramic disc caps or the green
> rectangle shape caps which I assume are mica caps.  I'm guessing one of
> the ceramics or mica caps is bad and causing the lightning crash sound
> in the audio?
>
> Thanks for any help.
>
> 73
>
> Stan
> KM4HQE
>
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