Component reference · HF start parts
TIG HF spark gap, discharge resistor and HV diode testing
Use this component page after the HF command and relay path have been checked. It covers the parts most often involved in weak or missing TIG high-frequency start: spark gap, discharge resistor, HV diode/silicon stack, boost transformer, relay contacts and HF cable/coupling path.
Component checklist
| Component | Normal role | Failure clue |
|---|---|---|
| Spark gap / discharge gap | Creates rapid high-voltage discharge pulses for HF ignition. | Dirty, too wide, too narrow or carbon-tracked gap gives weak/intermittent HF. |
| Discharge resistor | Limits and stabilizes discharge energy. | Open or cracked resistor can stop HF or make the pulse unstable. |
| HV diode / silicon stack | Shapes or rectifies high-voltage pulse path. | Short/open stack can eliminate HF or overload transformer/relay parts. |
| Boost transformer | Raises voltage for HF oscillator/discharge path. | Burnt secondary lead, insulation failure, open winding, weak spark. |
| HF relay | Switches HF power only during start window. | Click with no contact transfer, stuck contacts, HF remains on. |
| HF cable / coupling coil | Transfers HF pulse to torch/output path without carrying main current directly. | HF leaks inside cabinet or does not reach torch. |
Recommended order
1. Visual inspectionLook for burnt leads, cracked parts, carbon tracking and loose HF cable.
2. Command/relay checkVerify relay command before testing HV components.
3. Passive checksCheck resistor continuity and obvious open transformer winding where safe.
4. Gap serviceClean and set gap only to the machine's service specification.
5. Output path checkInspect torch lead, work return and coupling path before replacing the board.
Do not over-adjust the spark gap
A wider gap is not automatically better. Incorrect gap can reduce ignition, increase EMI, stress the transformer and damage nearby electronics. Use manufacturer values when available.