If you hear the fan speed increase slightly somewhere between first and second crack, the Popper might have hit it’s temperature limit. Here’s a video showing what it sounds like, and what to do…
The Popper A machine for roasting coffee. Or the person operating it! The basic requirements for a coffee roaster are a heating element that gets suitably hot and a mechanism for agitating the beans.: A mechanism for More has a thermal switch which prevents the roaster from getting too hot too fast. This can kick in some time after First crack in one of two distinct heat-induced pyrolytic reactions in coffee. It is distinguished by a cracking or popping sound in the coffee, and occurs between 390 and 410 degrees Fahrenheit in most coffee More, as the machine nears After First Crack, a roast reaction around 440 to 450 degrees that is distinguished by a snapping sound. Second Crack is the second audible clue the roaster-operator receives about the degree-of-roast, following First Crack. Whereas More. It’s annoying perhaps but required to have for UL certification.
If this is causing issues, you might get better results with a slower heat ramp getting to first An audible popping sound heard during roasting. In coffee, one refers to "first crack" and "second crack," which come from two different classes of chemical reactions.: An audible popping sound heard during roasting. In coffee, More, and slowing down the roast between 1st and 2nd cracks. We have a page/video all about that: https://library.sweetmarias.com/roast-development-to-second-crack-in-popper-coffee-roaster/
If it’s still an issue it is quite easy to modify the position of the switch a bit, pushing it up higher on the roast chamber. But opening up a roaster means voiding the warranty so consider that! Here is a video dedicated to explaining the thermal cut off switch and how to address the issue.