RetireeJay wrote:IRLB8743PBF-ND
The operation of both heater circuits is that one terminal is permanently connected to +12V, and the other terminal gets grounded through the N-channel MOSFET when calling for heat. So if you have some other pathway to ground that bypasses the MOSFET, your heater will always be on and it isn't the MOSFET's fault.
daveculp wrote:It appears I simply need to test the resistance between the two terminals on the screw terminal correct? What readings am I looking for if the MOSFET is bad?
Mooselake wrote:Does the displayed bed temperature increase as it warms up, or is constant? If constant, what is it? Perhaps it's a problem with temperature sensing, like it fell off the board. That problem has lead to extruder fires, not sure if the heated bed would get hot enough.
Kirk
daveculp wrote: Another experiment I did. With only ONE of the two heat bed wires (doesn't matter which one) plugged into the first screw terminal of the heat bed (the one closest to the hot end plug) and the other wire left unconnected and floating the heat bed will still heat uncontrollably with the power on and the board screwed to its standoffs.
RetireeJay wrote:The solution could be as simple as adding a piece of paper between the heat bed and the underlying metal bed.
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