Scorching can be caused by:

1. Drum too hot. On my roaster, charge temperature above 160C risks scorching with honey processed coffee. Not so much with the wet or dry processed coffee.

2. Drum speed too fast. When the centrifugal force causes the beans to be pushed against hot drum, scorching occurs.

These phenomenons are caused by local heat to be greater then the heat conductance of the bean. To lesser extend, it can also be seen in tipping, which occurs more commonly with Brazilian beans.

Depending on the roaster, when the vent is slightly open, the convection increases heat transfer, and therefore the rate of roasting temperature rise is faster. With larger vent opening, heat is lost therefore the opposite occurs. Water vapor carries the heat during the drying stage, so opening the vent too much during drying with too hot of drum temperature likely will increase scorching.

Some things for the OP to try will be, charge at lower temperature, close the vent during drying, increase the heat at end of drying, lower the heat just before expected first crack, and only open the vent slightly at first crack and not too much so the roast won't stall.

I too have the same problem with the thermocouples on my 500.
I did a couple of quick tests last night with ice and boiling water.
Checked against a pair of digital thermometers that do read 32 in the ice and reproduce the same temps as water is boiled the stock thermocouple read 35 in the ice and was 10 degrees short of the digital readings as water approached boiling.
I think some new sensors are in order.

*I opened the control board to the roaster to check the connections to the Omron Temp Controllers(O5CSL).
The sensors are 3 wire. I then went into the menu of the Controller to check the Input Type in the Initial Settings. Mine are set to 8 for a 3 wire Platinum Resistance Thermometer. The Settings would only accept 8 or 9.
Given all of that, my guess is that the machine is using Pt100 sensors.
I am wondering if changing the Temp Input Shift will bring the measured temps into line with the actual temps.

Thanks for the info and advice henry! I'll have to try a lower charge temp, because I have been charging at right around 200 degrees celsius.

I was also curious if the probe inaccuracies could be cured by some sort of programming change. That is definitely not something that I have knowledge of but I wonder if the santoker guys might have a solution.

I took a closer look at the Omron Controllers.
They are E5CSL-RP type. This can be seen on the back side of the unit.
These are for Pt100 probes only.
There is a E5CSL-*1TC for thermocouples.
They do have an adjustment for Temp Input Shift. This will add or subtract degrees to the measured value.
It does not seem to be useful for adjusting these probes because they do not have a consistent deviation across there range of use.