The Swix 73 wax iron uses an electronic feedback control system to maintain a constant base plate temperature. The reading from a temperature sensor in the base plate determines when power is applied to the resistance heaters in the plate. Power to the heaters is switched on and off using a STMicroelectronics T410-600T Triac chip. I've had this chip fail twice. The symptoms are obvious- the LED light on the front of the iron is on continuously, but the base plate stays cold.

It's easy to replace the chip if you have a simple soldering iron and a little experience with soldering electronic components. One first needs to remove the plastic case on the iron. It is held on by two screws accessible from the bottom rear, and two screws hidden under the front trim plate. The trim plate can be easily popped off with a small slot screwdriver as shown below.
Removing the small trim plate

The red plastic cover can then be pulled off revealing the white circuit board that controls power to the heater elements. Disconnecting the black power line input leads and the thick green wires connected to the base plate heater allows the circuit board to be lifted out. Label all the leads and sketch a diagram showing how they connect before you start dismantling!

The T410 chip is the one with the large metal heat sink extension pop riveted to the board as shown below.
Arrow shows rivet holding T410 chip

To replace the chip it is first necessary to drill or grind out the soft metal rivet. The three leads on the chip then need to be de-soldered using a soldering iron and some solder wick. Once enough solder has been removed to free the chip from the holes in the circuit board it can be pulled out with pliers. The new chip can then be inserted. I used a screw and some washers to hold the replacement chip in place and try and provide some heat sinking for the chip, which runs very hot and hence is prone to failure. Once the chip is physically attached to the board its three leads can be soldered in place and any protruding parts of the leads cut off with wire cutting pliers. It's a good idea to temporarily attach an alligator clip to the lead near the chip as a heat sink when soldering. The circuit board can then be placed back on its locating pins, the power cable and heater wires reconnected, and the plastic case re-assembled.

T410-600T chips are available by mailorder from Digikey ( Current cost is $1.30 per chip with a $8 shipping charge. I'd suggest ordering a few chips since they seem to fail frequently.

The Swix 73 is an excellent wax iron, and expensive enough to be worth repairing. If anyone comes across these directions and uses them to repair a T73, please send me a note!

Garry Tarr

February 2018