[R-390] Lightning crashes in audio

[Stan Gammons]

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