Byspeed z axis will not calibrate

[Cjammo]

Hi all

Trying to fix a Byspeed 5.2 (cnc96) the machine will not celibate.
The machine just drives down and over travels

I have replaced the Lcsens broad and diode holder a number of times and have tested them in another machine and they work fine.
Have also put in a working zwcon2 card with nothing changing..
Cables all check out fine
Any hints on getting the machine working
Thanks