Vintage Synth Repair

I'm scoping signal coming in and the buss for modulations.  Both
clean.  No matter what mod setting there is a huge pop unless I turn
the cutoff all the way down.  Even with ADSR and the rest down, if the
cutoff is up, this pop signal whose peak exceeds the ADSR's peak at
that mix node.... will emerge from the filter.  It's not showing up on
the rails.   Soo....hmm...it's kind of noisy too it seems.  So
something is probably open and it's an antenna feed to it.  It does it
more when keys are struck than trigger.  Proximity of signal to open
point I'm guessing?

Anyone else seen this before?  What a pain.  Sometimes I get these
things on ebay where..someone just plays them into the ground.  The
machine like develops 5 different problems that I'd fix...but they
just keep putting up with it until the thing totally dies.  Hehe. I
have a JUNO106 that I fixed here and the seller of course not only
didn't mention no cord came with it...he just said it stopped working.
 After i replaced the clock buffer and got itup...I found
that...ugh..it had two bad vcf/vca modules.   Or the supposedly ok
MKS30 I got that had FOUR bad ones.  I kid you not.  Anyone else have
that kind of luck?  I mean..you really learn to fix
stuff...but...someday..I'd like to make a few bucks too! :-)  -bob