When we first started selling the Fresh Roast SR 300 and SR 500, we recommended a certain technique for an even roast; namely, to remove the chaff collector and stir the coffee during the initial stages of the roast when the beans are heaviest. It turns out that this results in an inordinate amount of chaff getting sucked back into the base of the roaster (because the fan is drawing in air to cool the roaster) and over time it chokes the unit. Eventually the unit will no longer get hot and the chaff in the base presents a fire hazard.
So we have modified our recommendation and suggest you do what Tim Skaling of Fresh Beans does to get an even roast: Run the machine for 1 minute with beans, then hit the COOL button for 30 seconds. Then turn the machine back on to finish the roast. With very dense beans, use the COOL cycle twice during the roast sequence. If you do remove the chaff collector during the roast, be sure to replace it as soon as possible. You might also want to open the base of the unit from time to time and vacuum out any chaff that has found its way inside (sort of a good idea with any machine). We have updated the annotations on the YouTube videos too on our Fresh Roast Details page.