When plasma not fires,  

1. Start from CNC, check if  Initial sense( IHS) work or not,

If torch lift down touch plate and up ( IHS) works,   CNC's arc start to THC's  IHSARCON( Pin4 on TO CNC) is ok.  If not,  problem is on this wiring,  or CNC's arc start output has problem.

2. IHS works ok  but no fire,   means THC receives arc start signal from CNC, but not send out arc start signal to plasma,  check the wiring between THC's arc start signal to plasma's arc start.

3. If the wiring is ok,  Press Arc Test button on THC panel,   torch should do IHS and fire;    after IHS,  The ARCON LED on THC panel turns on, but  plasma not fire,   please check plasma's arc start relay, it might have problem,

If the ARCON LED not turn on after press Arc Test,  that means THC's arc start output signal has problem.

 

Once the problem is positioned,  rest work is simple.