Fault
TIG no high frequency
HF board, spark gap, high-voltage transformer, trigger chain and no-HF diagnosis.
What no high frequency means
A TIG welder may still have output capability but fail to initiate the arc through HF start. No HF can be caused by the torch trigger path, mode switch, HF enable signal, HF relay, spark gap, high-voltage capacitor, high-voltage transformer or the control board.
HF start flow
Torch switch / pedal
↓
Control board HF enable
↓
HF relay or switching transistor
↓
HF oscillator / transformer
↓
Spark gap and HV capacitor
↓
HF coupled to output
↓
Arc starts without touching tungsten
Checks
| Check | Normal / Expected | Abnormal Meaning |
|---|---|---|
| Spark gap | Clean and correctly spaced | Dirty or wide/narrow gap prevents HF |
| HF fuse/resistor | Continuity | Open path disables HF |
| HF transformer | No open winding | No high-voltage pulse |
| Trigger signal | Reaches control board | Torch or connector fault |
| Mode switch | TIG/HF mode selected | Switch path disables HF |
| Output clamp/torch | Good continuity | HF cannot couple effectively |
Repair warning
HF circuits generate high voltage. Do not probe the HF output with ordinary meter leads. Inspect and test with appropriate isolation and procedures.