Geeetech

Yes you are correct, the MOSFET controls the power to the bed. There are three of them on the board near the power connectors for the extruders and heat bed. Like I said before it sounds like one might have died on your board. Another option could be that the digital pin driving the MOSFET has died....

Sounds to me like one of the MOSFETs might have died.

If it's giving power constantly the MOSFET might be stuck, could there be a short on the board?

If the hardware has failed there's not much you can do unfortunately.

Just in case anyone else has similar issues I got around the need to solder when installing my 3d touch. It turns out that if you don't need the 5th stepper you can steal 5v from it's socket. I describe it here: http://antony-jordan.co.uk/3d-touch-tutorial.html#wiring The bottom two pounds on the so...

I had a similar issue. Tried a card didn't work. Put the card from my camera in and it worked. Put the failed card in my camera and formatted it using the camera and it now also works in the printer. I guess the FAT driver in the firmware isn't very robust and needs the card to be formatted with jus...

Are you able to post a picture of your extruder, it may allow people to help you better.

I don't see any metallic bed material in the photos you have posted. What is the sensor triggering on, do you have a metallic plate under the heat bed or is the sensor sensitive enough to pick up on the traces inside the heat bed PCB? I have been considering adding an upgrade such as this to my prin...