Circuit
TIG and plasma high-frequency start circuit
HF transformer, spark gap, high-voltage capacitor, trigger path, pilot arc and arc-transfer feedback.
What no pilot arc means
A plasma cutter with air flow but no pilot arc can fail in the torch trigger circuit, air pressure interlock, HF start board, pilot arc relay/resistor, torch consumables, work clamp or arc-transfer feedback path.
Pilot arc flow
Torch trigger
↓
Air pressure OK
↓
Control board enable
↓
HF start board fires
↓
Pilot arc path conducts
↓
Arc transfers to workpiece
↓
Main cutting current enabled
Diagnostic table
| Check | Normal / Expected | Abnormal Meaning |
|---|---|---|
| Air pressure switch | Closed/valid when pressure OK | Control board blocks output |
| Torch consumables | Correct and not worn | No stable pilot arc |
| HF board | Fires on trigger | No ignition |
| Pilot arc relay/resistor | Conducts pilot path | No pilot current |
| Work clamp | Good connection | Arc cannot transfer |
| Arc-transfer feedback | Changes after transfer | Machine may shut pilot off |
Common causes
- Low air pressure or faulty pressure switch.
- Worn electrode/nozzle.
- HF board not enabled.
- Pilot arc relay/contact failure.
- Feedback signal missing after arc transfer.
- Control board protection state.
Related repair map
Follow the evidence path from symptom to measurement, circuit and repair case.