C6 is a electrolytic capasitor of 4.7uF/16V. Obviously an error in the parts list, sorry.
If you get 600V, at least the high voltage board is OK. This is a new record, the most i have got is 350V.

If it sparks by itself, it sounds like you have activated the test function, or have a problem with the PIC.
Try removing the wire bridge between the 2 parts of the board, and see if it stops.

The wire in the pictures is thicker than 0.1mm, it is not a picture of my torroid.
I used 0.1mm, but it is not important.

Jon-Magne