I went through this when I tested some modified 28BYJ steppers.
At least one thermistor has to be plugged in to make Marlin work. I have some spare thermistors, so it was no biggy.
If you don't have a thermistor, just wire some random resistor ( lower than 100kOhm ) to the thermistor header.
You can ignore all the PID and thermal runaway stuff.
Just make sure, you have set all the endstop and stepper settings same for all three axis'.
Don't try to cheat like:"reversing stepper-direction & reversing homing == carrier running in the right direction".
Turn around stepper-connector, if one stepper runs the wrong way, but keep the firmware settings equal.
-Olaf
Edited 1 time(s). Last edit at 12/08/2015 04:25AM by o_lampe.