I have an Ungar 9911 soldering iron handpiece without the controller. Looks new.
I thought it would be trivial to build a temperature controller. I can make it hot. There is some PTC going on as the current goes down as the iron heats up.
I expected some feedback. The only other connector pins that have some connectivity measure 497 ohms independently of temperature. Can't use that for temperature monitoring.
Google has failed me. Anybody know how these work?