just had a burnout on my SC-x21, did not take long to find what happened.
the Vert size pot started to arc out on the center lead to the chassis.
https://i.imgur.com/mUX12ih.jpg
there is about 500v there and very little spacing there, and once it stared to arc and carbon, there was nothing to stop it.
It is powered from the HV boost so it really messed things up
I have it cleaned up and doped and waiting to dry
while i had it out, I too the chance to address the buzz-o-matic sound.