The oven control board [Kevin] designed is powered by USB and uses simple ON/OFF temperature control. The temperature inside the oven is measured using a MAX6675 K-type thermocouple amplifier. After having thrown the oven outside to contain the risk and let it cool down, [Kevin] started to investigate what may have been the cause of the incident . He discovered that his temperature reading was not correct, and that swapping the USB AC adapter with another resolved the problem. The chip reading the thermocouple needs a solid 5V reference for accurate readings. The mains adapter he was using is non-branded and he guesses that the 5V rail is super dirty. We’d love to see an oscilloscope screenshot… perhaps encouragement in the comments section will convince him to publish a follow-up?