thermistor - firmware problem

[wevefor]

Hello,

Earlier this year I was tinkering with adding a dual-nozzle Mk8 extruder hotend to my Geeetech A10M printer, this involved changing the firmware and building my own custom Marlin.

I have now reset all the hardware on my A10M to how it was originally, and to reset the firmware I flashed it with the "A10M_G05(GT2560V4+CH340)" firmware on the downloads page of the Geeetech website. However my hotend thermistor is showing 3-4 degrees C instead of 20-22 degrees C which I know is my room temperature. The print bed thermistor is working just fine.

I contacted customer service and they said that I had installed the correct firmware, but to be on the safe side I tried all the others on the website as well. I also tried building my own firmware for the stock A10M but the same issue occurred. So far I have also tried replacing the thermistor with two other 100k NTCs, as well as replacing the hotend adapter board with a new one, but I still have the same issue. I checked the hotend connector cable bundle which is fine, as well as its connection to the main motherboard which is also fine.

I should mention that I purchased this printer in August of 2020 from Banggood. My suspicions are that either the printer shipped with a slightly tweaked thermistor profile, or that some electronics on the circuit board have changed and accidentally given the connection more resistance, resulting in a lower shown temperature.

It would be great if anybody has a version of the August 2020 firmware that they could send, or any other advice as to how I can fix this issue.

Thanks in advance.