First, you are talking about Arduino replacing the sequencing and control or starting the torch and maintaining cutting plasma, right?
You are NOT talking about making some X-Y CNC cutter, right?
Do you understand the sequence diagrams in the manual?
WHICH model do you have??
This is complex circuitry and you have a ways to go to understand what to do.
I have the PCM-750i
I am talking about the operation of the plasma cutter itself. It's a portable unit and has no CNC system.
The main board controls about everything through relays and SCRs. The symptiom I'm combatting and from what I can tell from forums is the condemning factor is the fault light being on all the time and only the pilot LED being lit. There are two other status LEDs that should be lit or flash to indicate status but, they're doing neither!