Circuit path · HF ignition

TIG HF relay, transformer and discharge path

This page explains the functional path inside a TIG high-frequency arc-start circuit: control command, relay switching, boost transformer, discharge network, high-voltage shaping parts and output coupling. It is for diagnosis of no-HF, weak-HF and HF-stuck-on faults.

Circuit path

This page has a specific TIG HF role

This page focuses on the HF relay, transformer and discharge path. It should be used after the diagnostic route points to the HF power/discharge section.

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.

Functional HF path

Control commandTorch/control board requests HF during start interval.

Relay coilReceives control voltage and closes HF power path.

Relay contactsSwitch transformer primary or HF power feed.

Boost transformerRaises voltage for the oscillator/discharge network.

Discharge networkResistor, capacitor, gap and HV silicon shape pulses.

Coupling pathHF energy is coupled onto torch/output lead for ignition.

Where the path fails

Path section	Failure mode	Diagnostic clue
Command input	No start command from control board	No relay coil voltage during torch press.
Relay coil	Open coil or missing supply	No click and no primary power.
Relay contacts	Burned, oxidized or welded contact	Click occurs but transformer primary not energized, or HF stays on.
Transformer	Open secondary, burnt lead, insulation failure	Primary energized but no high-voltage output.
Discharge resistor / gap	Open resistor, dirty/wrong gap, cracked capacitor	Weak or inconsistent HF.
HV diode / silicon	Open/short high-voltage rectifier stack	No HF, unstable pulses or repeated component stress.
Coupling/output lead	Leakage, cracked insulation, bad connector	HF visible inside cabinet but not at torch.

Practical checks without unsafe probing

Listen and observe

Relay click, HF sound and visible leakage marks can localize the section before measurements.

Check primary side first

Low-voltage command and relay primary checks are safer than probing HV output.

Inspect coupling path

Loose HF cable, cracked insulation or dirty spark gap can waste HF energy inside the cabinet.

Safety boundary

Do not connect ordinary meters or grounded oscilloscope probes to the HF output. Use command-side checks first, then qualified high-voltage methods if required.