Did initial setup on my THC-300.  Fault light is on and has never gone out.  Also unable to get ark OK LED.  Applied 12 VDC to ark OK terminals as per instructions and still nothing.  When plasma is running manually, I can see a voltage on the readout, but because no ARK OK signal, machine starts torch, waits for signal, doesn't get one and shuts down the torch.  Have tried adjusting ark ok sensitivity pot and no luck.  Any body have any thoughts ??

Check your CT connections and polarity or arc good signal from Plasma unit.
Also check J6-1, J6-2.
Hope this helps.

Regards

KTM