I am having an issue recently with what seems to be insufficient power. I just did a 350g roast, starting at power 6, fan 1, then increasing the power to 7 or 8 to get the beans up to 300 degrees on the IRBT readout in about 3 minutes. Rate of rise is about 30 just before 300 degrees. What then happens is that from 300 degrees to about 390 degrees, I have to keep the power at 9 and fan at 1 just to keep the ROR over 20. The ROR starts to fall as the temperature increases above 300 even though the roaster is at maximum power and minimum fan. By the time the roast approaches first crack the ROR will have fallen to 20 or under at power 9. IT will then jump up as the roast approaches first crack and beyond and I can then cut power/increase fan to control the roast. On a bigger, 700g batch, once the roast hit 300 degrees the ROR started falling at maximum power, minimum fan, I could not keep it above 20, so it dropped quickly from 30 to around 20 until right before first crack.
One thing I noticed is that there is a fan (internal cooling?) that was running non-stop. I do not think this is the same fan as the fan controlling the roast because I could impact the ROR by adjusting fan speed.