I'm making a new printer (simple cartesian, no fancy stuff) using a ramps 1.4 board with an arduino mega. The problem is that when the hotend thermistor is plugged to the board, it resets the printer, same thing when the thermistor is unplugged. Not only that but the temperature that the board reads is aways 0. The thermistor (and the other 4 that I tested) is fine, around 100k as it should be. T0, t1 and t2 all are around 5.8 Ohms when the power is off, and 4.7 when power is on. And to top it all, when the thermistor is connected and the power is on, the arduino chip gets really hot (also tested with other arduino boards, same result), but keeps working for everything else. The Marlin firmware is fine too, since is the same config I use in my other printer (both printers are basically identical).
With all that said it seams clear to me that the problem is the ramps board, but I don't know what or if it could be fixed. I didn't find any questions about problems similar to this so I'm hoping someone could help me and anyone else with this problem.
Thanks a lot!
