Fault route · TIG HF start
TIG HF arc-start weak or missing diagnosis
Use this workflow when a TIG welder has gas but no HF, weak high-frequency start, intermittent start, HF relay click without spark, or HF that continues after arc transfer. Start from the first visible sequence result before opening the high-voltage path.
First split: gas, HF command, or main output?
No gas and no HF
Start upstream: torch switch, 24V/control rail, mode switch and bottom-board relay logic.
Gas works, no HF
Start with HF command, relay coil, relay contacts, transformer primary and HF board supply.
HF present, no arc
Check shielding gas, torch/work return, HF coupling path, main output enable and secondary output path.
Evidence order
Symptom table
| Observation | Likely area | Next check |
|---|---|---|
| Gas flows, no HF sound or spark | HF command, relay coil, HF board supply | Check relay drive and control input before HV parts. |
| Relay clicks, no spark | Relay contacts, boost transformer, discharge resistor, HV diode/silicon stack | Check primary-side voltage and visible component damage safely. |
| Weak HF spark | Gap/coupling contamination, transformer weakness, gas/torch return or leakage path | Inspect HF cable, torch connector, spark gap and cabinet leakage marks. |
| HF present but no arc transfer | Main output blocked or bad work/torch path | Check OCV/output enable, work clamp and secondary rectifier/output path. |
| HF stays on after arc starts | Arc-detect or cutoff logic | Check feedback/cutoff signal and HF relay release path. |
Do not confuse HF with welding current
A visible HF spark does not prove the main inverter/output stage is producing welding current. Conversely, a healthy main output cannot start TIG reliably if gas, torch return or HF coupling is missing.