John Heath wrote:



The layout relies on the two plate wires being in close
proximity so the out of phase electric fields cancel at a distance.




There is a third option. Stop being a hero.
You can not fix everything. Phone the customer
and say this is a tricky problem and that they
are better off taking it to the manufacturer for
service.



** The OP fixed the oscillation problem, after acting on my advice about cable dress. A previous repairer had been careless.


..... Phil