Using with thercouple in parallel with heater

[jducifuentes]

Hi there, I was looking for a project that can resurrect my old and broken Aoyue 701 desoldering gun. Original heater element has 4 wires (2 for resistor and 2 for thermocouple) but newer replacement comes only with 2 wires so thermocouple is wired in parallel with heater. I also checked that applying heat externally with hot air and measuring mV on wires.

My question/request is if can modify somehow your circuit to use this kind of heating elements.

I tested this heating element with a cheap t12/jbc/936 chinese clone solder board And apparently works but when reaching +-300ºC controller goes crazy and never stabilizies temp.

The approach I think is to make readings between pwm pulses to not get heater voltage over thermocouple.

Thanks in advance!