Hello everybody,
I just bought my first cheap Cr-10 clone with two Z axes and as expected there is a problem with nozzle temperature readings. The first time I turned it on the screen was blank and after some turn off-on’s it worked but the nozzle temp. was 77C right away without any heating. I thought the thermistor was damaged and after inspection it was true so I changed it for a spare one and the problem was the same. How I knew that the new one was working? I switched it with the heatbed thermistor socket and it showed the right temp. Even after disconnecting the new thermistor from the socket the temperature was showing around 75C as if this value has been locked on the screen. I have to point out that when I go to the menu and turn on the nozzle heating to 200C the tip starts to heat but he temperature reading stays at 75C for hours. The filament is melting but the printer does not start because it thinks the temperature is still 75C. There is this strange thing that when the printer is cold and turned on the temp. is 77C but after heating falls to 75C.
It seems that this could be a board issue but I’m not sure. I saw some guides hot to flash the board with a new firmware but I need a arduino uno. I have only the mega 2560 board and I think it could not be done with it. Has anybody some suggestions?
Thank you very much… 
