So I was able to create a crude schematic of the daughter board and part of the HV supply, but it didnt really help me with understanding the circuit so far.
Only a part of this board is duplicated, and that is the comparator part with HV sensing divider. Second input of the comparator is another voltage divider of 6k8 and 10k resistors, creating almost exactly 2 volts out of the 3.37V supply. This should mean the comparator will turn off the output once there is about 620V at the capacitor. This part of circuit doesnt have any connection to the rest of the board, or atleast i wasnt able to find any. The comparators and AND gates does have some conections to the MCU, but it looks like that part is driving only the output thyristor.
While measuring I found out the 10k resistor of the divider at main board was meauring about 5k, so i tried to desolder it, but apparently the double diode nearby was skewing the measurement. Then I was unable to solder it back and lost it later, so i have to find another one somewhere first
The double diode is marked LD3, so it should be BAT54S. It measures 300mV drop / 5,5kohm in forward , 1,2V / 8,2k in reverse. This looks kinda weird to me, but all the other LD3s on the board measure similiar values, so i guess it is a feature?
In same way the 10k resistors of the low voltage comparators measures 4,7k, but once again thats due to the comparators connected and since both measure the same, it is probably not a fault.
Edit: I have just noticed that those comparator parts are not exactly the same either, one comparator have HV sense at pin 1, the other at pin 3. Therefore when one comparator outputs high, the second is low and vice versa, however both outputs are just connected together.