[R-390] Lightning crashes in audio

[Francesco Ledda]

I would start at the audio amp and move up. Sectionalize the chain one step at the time until the noise disappears.

The last thing you want to do is to use the shotgun approach.

Best and good luck, K5URG

Sent from my iPad

> On Aug 15, 2020, at 21:43, Larry H <larry41gm at gmail.com> wrote:
> 
> 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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