Fault

TIG no high frequency

HF board, spark gap, high-voltage transformer, trigger chain and no-HF diagnosis.

Fault entry

This page has a specific TIG HF role

This page is the broad symptom entry for no high-frequency start. It should route users to the HF diagnostic and circuit/component references.

Related TIG HF start pages

TIG HF content is separated by user intent: broad fault entry, diagnostic route, general sequence, timing/cutoff subtopic, discharge-path circuit and component testing.

No high-frequency fault entryBroad symptom page for users starting with no HF start. HF weak or missing diagnosticStep-by-step route for gas but no HF, weak HF, stuck HF or no arc transfer. HF relay / transformer / discharge pathCircuit path for relay, transformer, discharge resistor, spark gap and HV diode evidence. 40V / 4s cutoff controlTiming/cutoff logic subtopic for HF start control. HF arc-start sequenceGeneral TIG HF start process page. HF component testingSpark gap, discharge resistor and HV diode checks after the path is isolated.

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.