Printhead heats up as soon as power is turned on.

Hi!

I'm assembling a Kossel XL, using an Arduino Mega, a RAMPS 1.4 Board, and Marlin.
connecting the Arduino to the computer is fine, Display shows normal temepratures around 37°C
But as soon as I power up the main power supply, the temperature on the display starts rising, reaching 300°C and a MAXTEMP Error after ~3min. It keeps rising afterwards, until I unplug the power.
Is this a RAMPS Issue, and if it is, does any of you guys know what might cause it? If I missed some information, please ask, I'm just new to the Topic.
best regards,
Arved

PS: Because I'm not sure where the problem lies, I also posted this in the Marlin forum.

Edited 1 time(s). Last edit at 03/17/2016 10:54AM by Arved.

I just had this issue when switching from RAMPS to Duet.

In my case, the issue was how I was wiring the endstops, essentially shorting (?) the power rail, 3v3, to ground instead of connecting the signal and ground pins. Double check to make sure your endstops and other wiring is correct.

Hi Kurzaa,
I'm sorry, but I don't entirely understand what you mean. if I test my endstops in pronterface, they work fine. what do you mean by shortening the power rail and 3v3?

I suggest you inspect the MOSFET area on the Ramps for solder bridges or other shorts. The hotend MOSFET seems to be switched on permanently.

yup, there was a soldering short on the RAMPS board's MOSFET section. Thanks!