SmartRap (RAMPS 1.4) runaway heat issue

Hello all,

I am using a Smartfriendz SmartRap printer with Arduino 2560/ RAMPS 1.4 controller, and the Smartfriendz Marlin firmware from their git.

I have a runaway heat issue - heat runs away when motors are jogged to position the head, and when PID Autotune is used, the hotend does not heat up at all.

I am using a 100W power supply (as I do not have a heatbed) and it seems to move the motors fine, and heat the hotend fine, its just uncontrollable.

Is it possible I have a dud MOSFET on the RAMPS? Please note, until motors are activated, the hotend doesn't heat up - only once the motors are jogged, thats when I get a runaway.

Many thanks in advance for any help!

Boris.

Ok, I flashed a regular Marlin firmware into the SmartRap, and connected the extruder to D8. Heat is now working as expected.

However, the extruder motor refuses to work. I've checked the config file, everything seems to check out.

Any thoughts?