QIDI Tech 1 Part Fan Controller

Unless you are printing only ABS you need this modification. It allows you to control the speed of the parts fan which significantly improves control over printed parts quality.
You need to print the box, squeeze into it the controller (might need to do a little filing) and wire it between the main board and the fan.
I purchased the controller from here:
https://www.aliexpress.com/item/DC-Motor-Speed-Control-PWM-Controller-6V-30V-5A-13KHz-Digital-Display/32843001132.html?spm=2114.13010708.0.