I have a 530 record that I removed the motor capacitor from when I got it, and ever since then it's been spitting when the motor starts and sparking a lot more than is comfortable.
A post from a Facebook group made me consider replacing it again recently so I ordered the components locally (2x2200pf and 1x0.1μF capacitors + 1x2.2MΩ resistor), twisted them together and screwed them into the two input power junctions.
She is now behaving perfectly, no spitting, no sparking.
This is a knee control machine, so all the capacitor stuff is wired in at the motor. If you're going to do this, make sure the components that carry mains current are reliably insulated. I had fairly long bits of wire poking out so I wrapped them with plastic wire insulation, and used electrical tape to hold everything in one place.
My 530 has a two prong plug and therefore not earthed, so a live wire (240V here in Australia) touching the head could be deadly.
Here's a really useful reference page that I used. Some of the explanations are written in German in the diagrams, so a knowledge of German or Google translate will be helpful
https://www.occaphot-ch.com/bernina-...ion-capacitor/