Internal and external spares for an AC/DC TIG inverter power source: how to identify the right part, what fails, and how to work safely.
How do I identify the right spare part for my AC/DC TIG inverter?
Start with the rating plate on the machine, which gives information about the manufacturer, supply requirements, performance and suitability for use. Note the type, serial number and any version marking, then find the matching parts list or service documentation from the maker.
The part number printed on the old item, where there is one, helps confirm the match, but do not rely on appearance alone. Boards, diodes, transformers and connectors often look alike while differing in ratings or fit between versions. If you are unsure, our team can help you work out which part your machine's documentation points to.
What are the main groups of internal parts in a TIG inverter?
An inverter power source converts the mains AC to high-frequency AC, steps it down through a transformer to welding voltage, and then rectifies it to DC. So the main groups are the input stage and its protection, the switching or power board, the high-frequency transformer, the output rectifier (often a diode board or card), the control electronics, and the output connections.
On an AC/DC machine there is additional circuitry to produce the AC output. Spares are usually listed by these groups in the maker's parts list. The exact layout differs from model to model, so use your own documentation.
Who should replace internal parts such as a diode card, transformer or shunt?
A competent person, not the user. The HSE says repairs should only be carried out by a competent person, meaning someone with the skills, knowledge and experience to do the work safely. Maker manuals for AC/DC TIG machines say maintenance should only be done by a qualified person, with the machine disconnected from the mains and a wait before internal work, because internal voltages and currents are high and dangerous.
The wait time and any discharge procedure are machine-specific, so follow the service manual rather than assuming. If you are not qualified, send the machine to a service engineer who can fit the part and test it afterwards.
What signs mean I should stop using the machine and have it checked?
The HSE says to stop using equipment immediately if it appears to be faulty and have it checked by a competent person. Signs to take it out of use include a damaged plug or connector, a cable that is loose or has been repaired with tape, internal wires showing, and burn marks or stains that suggest overheating.
For a TIG inverter, also watch for a tripped supply protection device, a burning smell, unusual noises, error codes that keep returning, loss of output or an unstable arc. Do not keep trying the machine, and do not remove covers to investigate unless you are qualified.
If a diode card or power board fails, is replacing just that part enough?
Sometimes, but not always. A failed board can be the result of another fault elsewhere, such as a failed protective part, a poor connection, overheating or a supply problem. If the cause is not found, the new part may fail too.
A qualified technician will normally check the related parts, connections and cooling as well as the part that has visibly failed, following the maker's service procedure. Giving the technician the rating plate details, the error code shown and a description of what happened when it stopped helps them work out the cause faster. Treat any quick fix that bypasses a protective part as unsafe.
What does a varistor do, and why might it need replacing?
A varistor is a protective part that is intended to limit short voltage spikes so they do not reach the more sensitive electronics. Repair accounts commonly find that a varistor on the mains input has failed after a surge, sometimes along with a fuse or breaker tripping.
Because it is protective, a failed varistor should be replaced with the correct type as specified in the maker's parts list. Leaving it out or fitting a part with a different rating removes protection for the rest of the machine. As with other internal parts, the work should be done by a competent person, and the cause of the failure should be looked into.