Best reach out to support@snapmaker.com. Want to say they are $150-ish for a new controller - they don’t sell components, only assemblies 
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There is no FET on that pin, it’s a signal from the mcu to the stepper driver in the toolhead.
Support has a special firmware version that will redirect all of the controls for the toolhead to the next port down. A copy of it is posted here: Laser toolhead went BANG! - #30 by mjlowe75