So a couple of years ago now (time files) I “upgraded” from the digital control on my K40 to analog control with amp meter and power pot. The power pot is a multi turn 5K ohm variable resistor recommend by @donkjr .
I use my k40 quite a bit and I’ve recently noticed that the voltage I measure across the pot, to determine a power setting, was bouncing around a lot when I turned the knob for the pot. Hooked up my meter and the pot was very noisy with the resistance bouncing around quite a bit. So it was obviously time to replace the pot.
Could not find a listing for a single pot like I originally bought so I bought this 2 pkg that came with knobs and now have a back up.
Easy fix with unsoldering and re-soldering some wires.