Bed starts heating immediately and won't stop

I’ve been using my MP3DP for a few months now and all of a sudden yesterday I noticed the bed heat was at around 100C when my print only called for 50C. I thought is was just an anomaly, but when I went to start printing more parts this evening the bed started heating as soon as I plugged in my power supply. The display shows no set temp and there’s there’s no little wavy lines above the bed heat icon. Any ideas?

I’m using a RAMPS 1.4 board with the Marlin 2 firmware from the V1 Github, and an ATX power supply.

Sounds like the mosfet is stuck on.

Ahh right. Well, I have a box of harvested components laying around here somewhere. I’ll see if any are compatible with the ones on the RAMPS. At least its probably one of the easier components to replace.

Thanks man

Definitely something wrong with that MOSFET. I plugged it in just long enough to raise my Z past my control box and the thing burned me when I touched it!

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That was it. I had a handful of Vishay SUP70N03s that were close to the ST Semi P55NF068 in specs. Printing calibration cube, nothing has caught on fire yet. Thanks again for pointing me in the right direction. :+1:

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