The Resistance Soldering Unit (RSU) that I bought was a second-hand unit and appears to be a home-made unit. It was nicely finished but I wanted to check it out for safety as potential mains voltages and hand held probes do not go together! I therefore opened the box and checked that all the wiring was safely connected and that various terminals etc. we’re properly insulated. I added some heat shrink tubing to a couple of connections but apart from that it was a well constructed unit based on a multi-tapped transformer.

One thing that was missing was any indication that the unit was plugged into a live mains socket and whether the foot pedal that activates the unit was being accidentally or deliberately being pressed. Because there is no isolating mains switch on the unit I added, whilst safety checking the unit, an amber neon lamp to indicate it was connected to a live mains socket and also a green neon lamp to indicate whether the foot switch was being pressed.

I have also added labels to indicate the various voltages available from the output sockets.